Khác biệt giữa bản sửa đổi của “Giảm thiểu biến đổi khí hậu”

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Theo [[Báo cáo đánh giá thứ năm IPCC|báo cáo đánh giá]] năm 2014 của [[IPCC]] "Việc giảm thiểu là một lợi ích công cộng; thay đổi khí hậu là một trường hợp '[[Bi kịch của mảnh đất công|cha chung không ai khóc]]'. Giảm thiểu tác động của biến đổi khí hậu một cách hiệu quả sẽ không đạt được nếu mỗi đối tượng (cá nhân, tổ chức hoặc quốc gia) hoạt động độc lập theo lợi ích ích kỷ của chính mình (xem hợp tác quốc tế và [[Mua bán phát thải Cacbon|mua bán thải carbon]]), cho thấy phải có hành động tập thể. Mặt khác, một số hành động thích ứng có đặc điểm của một lợi ích cá nhân vì lợi ích của các hành động có thể mang tính tích luỹ trực tiếp hơn cho các cá nhân, khu vực, hoặc các quốc gia thực hiện nó, ít nhất là trong thời gian ngắn hạn. Tuy nhiên, việc tài trợ cho các hoạt động thích ứng vẫn là một vấn đề, đặc biệt đối với các cá nhân và các nước nghèo."<ref name="AR5-WG3-Chap3">{{citation|chapter=Social, Economic, and Ethical Concepts and Methods, Executive Summary|title=Climate Change 2014: Mitigation of Climate Change|chapter-url=http://ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_chapter3.pdf}}, in {{harvnb|IPCC AR5 WG3|2014|p=211}}
Theo [[Báo cáo đánh giá thứ năm IPCC|báo cáo đánh giá]] năm 2014 của [[IPCC]] "Việc giảm thiểu là một lợi ích công cộng; thay đổi khí hậu là một trường hợp '[[Bi kịch của mảnh đất công|cha chung không ai khóc]]'. Giảm thiểu tác động của biến đổi khí hậu một cách hiệu quả sẽ không đạt được nếu mỗi đối tượng (cá nhân, tổ chức hoặc quốc gia) hoạt động độc lập theo lợi ích ích kỷ của chính mình (xem hợp tác quốc tế và [[Mua bán phát thải Cacbon|mua bán thải carbon]]), cho thấy phải có hành động tập thể. Mặt khác, một số hành động thích ứng có đặc điểm của một lợi ích cá nhân vì lợi ích của các hành động có thể mang tính tích luỹ trực tiếp hơn cho các cá nhân, khu vực, hoặc các quốc gia thực hiện nó, ít nhất là trong thời gian ngắn hạn. Tuy nhiên, việc tài trợ cho các hoạt động thích ứng vẫn là một vấn đề, đặc biệt đối với các cá nhân và các nước nghèo."<ref name="AR5-WG3-Chap3">{{citation|chapter=Social, Economic, and Ethical Concepts and Methods, Executive Summary|title=Climate Change 2014: Mitigation of Climate Change|chapter-url=http://ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_chapter3.pdf}}, in {{harvnb|IPCC AR5 WG3|2014|p=211}}
</ref>
</ref>

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==Greenhouse gas concentrations and stabilization==
{{See also|Greenhouse gas#Removal from the atmosphere and global warming potential}}

{{Multiple image
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|image1=Stabilizing carbon dioxide emissions at their present level will not stabilize its concentration in the atmosphere.png
|image2=Stabilizing the atmospheric concentration of carbon dioxide at a constant level would require emissions to be effectively eliminated.png
|alt1=refer to caption and adjacent text
|alt2=refer to caption and adjacent text
|width=320
|caption1=Stabilizing CO<sub>2</sub> emissions at their present level would not stabilize its concentration in the atmosphere.<ref name="meehl stabilizing ghg concentrations"/>
|caption2=Stabilizing the atmospheric concentration of CO<sub>2</sub> at a constant level would require emissions to be effectively eliminated.<ref name="meehl stabilizing ghg concentrations"/>}}

One of the issues often discussed in relation to climate change mitigation is the stabilization of greenhouse gas concentrations in the atmosphere. The [[United Nations Framework Convention on Climate Change]] (UNFCCC) has the ultimate objective of [[Avoiding Dangerous Climate Change|preventing "dangerous" anthropogenic (i.e., human) interference of the climate system]]. As is stated in Article 2 of the Convention, this requires that greenhouse gas (GHG) concentrations are stabilized in the atmosphere at a level where [[climate change and ecosystems|ecosystems]] can adapt naturally to climate change, [[climate change and agriculture|food production]] is not threatened, and [[economics of global warming|economic development]] can proceed in a sustainable fashion.<ref>{{cite book
|year=2007
|author=Rogner, H.-H.
|contribution=1.2 Ultimate objective of the UNFCCC
|title=Introduction
|series=Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
|editors=B. Metz |display-editors=etal
|url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch1s1-2.html
|publisher=Print version: Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. This version: IPCC website
|accessdate=2011-06-07|display-authors=etal}}</ref>

There are a number of anthropogenic greenhouse gases. These include [[carbon dioxide]] ([[chemical formula]]: {{CO2}}), [[methane]] ({{chem|CH|4}}), [[nitrous oxide]] ({{chem|N|2|O}}), and a group of gases referred to as [[halocarbon]]s.<ref>{{citation
|title=Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|author=Forster, P.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-2-1.html FAQ 2.1 How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences?]
|chapter=Ch. 2: Changes in Atmospheric Constituents and in Radiative Forcing
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2.html
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG1|2007|p=135}}</ref> The emissions reductions necessary to stabilize the atmospheric concentrations of these gases varies.<ref name="meehl stabilizing ghg concentrations">{{citation
|title=Climate Change 2007: Working Group I: The Physical Science Basis
|author=Meehl, G.A.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-10-3.html FAQ 10.3: If Emissions of Greenhouse Gases are Reduced, How Quickly do Their Concentrations in the Atmosphere Decrease?]
|chapter=Ch. 10: Global Climate Projections
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch10.html
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG1|2007|pp=824–825}}</ref> {{CO2}} is the most important of the anthropogenic greenhouse gases (see [[radiative forcing]]).<ref>{{citation
|title=Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|author=IPCC
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-human-and.html Human and Natural Drivers of Climate Change]
|chapter=Summary for Policymakers
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spm.html
}}, in {{harvnb|IPCC AR4 WG1|2007}}</ref>

There is a difference between stabilizing {{CO2}} emissions and stabilizing atmospheric concentrations of {{CO2}}.<ref>{{cite web |date=January 2009 |author=U.S. Climate Change Science Program and the Subcommittee on Global Change Research |title=Best practice approaches for characterizing, communicating, and incorporating scientific uncertainty in decisionmaking |editor1=Granger Morgan |editor2=H. Dowlatabadi |editor3=M. Henrion |editor4=D. Keith |editor-link4=David Keith (scientist) |editor5=R. Lempert |editor6=S. McBride |editor7=M. Small |editor8=T. Wilbanks |pages=10–11 |url=http://www.globalchange.gov/publications/reports/scientific-assessments/saps/311 |publisher=National Oceanic and Atmospheric Administration, Washington D.C., USA. |accessdate=2010-06-07 |deadurl=yes |archiveurl=https://web.archive.org/web/20100527134225/http://www.globalchange.gov/publications/reports/scientific-assessments/saps/311 |archivedate=2010-05-27 |df=}}</ref> Stabilizing emissions of CO<sub>2</sub> at current levels would not lead to a stabilization in the atmospheric concentration of CO<sub>2</sub>. In fact, stabilizing emissions at current levels would result in the atmospheric concentration of CO<sub>2</sub> continuing to rise over the 21st century and beyond (see the graphs opposite).

The reason for this is that human activities are adding CO<sub>2</sub> to the atmosphere faster than natural processes can remove it (see [[carbon dioxide in Earth's atmosphere]] for a complete explanation).<ref name="meehl stabilizing ghg concentrations"/> This is analogous to a flow of water into a bathtub.<ref>{{cite journal
|year=2007
|title=Understanding public complacency about climate change: adults' mental models of climate change violate conservation of matter
|doi=10.1007/s10584-006-9107-5
|author1=Sterman, J.D. |author2=L.B. Sweeney
|journal=Climatic Change
|url=http://jsterman.scripts.mit.edu/docs/Sterman-2007-UnderstandingPublicComplacency.pdf
|format=PDF
|accessdate=2011-05-10
|volume=80
|issue=3–4
|pages=221–22}}</ref> So long as the tap runs water (analogous to the emission of carbon dioxide) into the tub faster than water escapes through the plughole (the natural removal of carbon dioxide from the atmosphere), then the level of water in the tub (analogous to the concentration of carbon dioxide in the atmosphere) will continue to rise.

According to some studies, stabilizing atmospheric CO<sub>2</sub> concentrations would require anthropogenic CO<sub>2</sub> emissions to be reduced by 80% relative to the peak emissions level.<ref name="us nrc co2 stabilization">[http://www.nap.edu/openbook.php?record_id=12877&page=21 2. Stabilization and Climate Change of the Next Few Decades and Next Several Centuries, p. 21], in: [http://www.nap.edu/openbook.php?record_id=12877&page=11 Summary], in {{harvnb|US NRC|2011}}</ref> An 80% reduction in emissions would stabilize {{CO2}} concentrations for around a century, but even greater reductions would be required beyond this.<ref name="meehl stabilizing ghg concentrations"/><ref name="us nrc co2 stabilization"/> Other research has found that, after leaving room for emissions for food production for 9 billion people and to keep the global temperature rise below 2&nbsp;°C, emissions from energy production and transport will have to peak almost immediately in the developed world and decline at ca. 10% per annum until zero emissions are reached around 2030. In [[developing countries]] energy and transport emissions would have to peak by 2025 and then decline similarly.<ref>{{cite journal|url=http://rsta.royalsocietypublishing.org/content/369/1934/20|title=Beyond 'dangerous' climate change: emission scenarios for a new world|journal=Philosophical Transactions of the Royal Society A|first1=Kevin|last1=Anderson|first2=Alice|last2=Bows|date=13 January 2011|publisher=|volume=369|issue=1934|pages=20–44|doi=10.1098/rsta.2010.0290|pmid=21115511|bibcode=2011RSPTA.369...20A}}</ref><ref>{{cite journal|url=https://dx.doi.org/10.1038/nclimate1646|title=A new paradigm for climate change|journal=Nature Climate Change|first1=Kevin|last1=Anderson|first2=Alice|last2=Bows|publisher=|volume=2|issue=9|pages=639–40|doi=10.1038/nclimate1646|year=2012|bibcode=2012NatCC...2..639A}}</ref><ref>Anderson K. (2012). Real clothes for the Emperor: Facing the challenges of climate change. The Cabot annual lecture, Univ. of Bristol. [https://www.youtube.com/watch?v=RInrvSjW90U&feature=player_embedded Video], [http://www.bris.ac.uk/cabot/documents/anderson-transcript.pdf Transcript]</ref><ref>[http://www.tyndall.ac.uk/radical-emission-reduction-conference-10-11-december-2013-register-here The Radical Emission Reduction Conference: 10–11 December 2013] {{webarchive|url=https://web.archive.org/web/20141027232316/http://www.tyndall.ac.uk/radical-emission-reduction-conference-10-11-december-2013-register-here |date=27 October 2014}}, sponsored by the [[Tyndall Centre]]. [http://tyndall.ac.uk/communication/news-archive/2013/radical-emissions-reduction-conference-videos-now-online Video proceedings] on-line.</ref>

Stabilizing the atmospheric concentration of the other greenhouse gasses humans emit also depends on how fast their emissions are added to the atmosphere, and how fast the GHGs are removed. Stabilization for these gases is described in the later section on [[#Non-CO2 greenhouse gases|non-CO<sub>2</sub> GHGs]].

; Projections
Projections of future greenhouse gas emissions are highly uncertain.<ref>{{citation
|title=Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|chapter=Ch 3: Issues related to mitigation in the long-term context
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3.html
|author=Fisher, B.S.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3s3-1.html Sec 3.1 Emissions scenarios]
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007}}</ref> In the absence of policies to mitigate climate change, GHG emissions could rise significantly over the 21st century.<ref name="rogner article 2">{{citation
|title=Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|author=Rogner, H.-H.
|chapter=Ch 1: Introduction
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch1s1-3-2-4.html Sec 1.3.2.4 Total GHG emissions]
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch1.html
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007|p=111}}</ref>

Numerous assessments have considered how atmospheric GHG concentrations could be stabilized.<ref>{{citation
|title=Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|chapter=Ch 3: Issues related to mitigation in the long-term context
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3.html
|author=Fisher, B.S.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3s3-3.html Sec 3.3 Mitigation scenarios]
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007}}</ref> The lower the desired stabilization level, the sooner global GHG emissions must peak and decline.<ref>{{citation
|title=Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|chapter=Ch 3: Issues related to mitigation in the long-term context
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3.html
|author=Fisher, B.S.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3s3-3-5.html Table 3.5, in: Sec 3.3.5 Long-term stabilization scenarios]
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007}}</ref> GHG concentrations are unlikely to stabilize this century without major policy changes.<ref name="rogner article 2"/>

{|
|-
|[[File:Projected carbon dioxide emissions and atmospheric concentrations over the 21st century for reference and mitigation scenarios.png|thumb|320px|upright|alt=refer to caption and adjacent text|Projected carbon dioxide emissions and atmospheric concentrations over the 21st century for reference and mitigation scenarios]]
|[[File:World energy consumption.svg|thumb|upright|none|333px|Rate of world energy usage per day, from 1970 to 2010. Every fossil fuel source has increased in large amounts between 1970 and 2010, dominating all other energy sources. Hydroelectricity has increased at a slow steady rate over this same period, nuclear entered a period of rapid growth between 1970 and 1990 before leveling off. Other renewables, between 2000 and 2010 have, having started from a low usage rate, began to enter into a period of rapid growth. 1000&nbsp;[[TWh]]=1&nbsp;PWh.<ref name="BP-Report-2012">BP: [http://www.bp.com/sectiongenericarticle800.do?categoryId=9037130&contentId=7068669 Statistical Review of World Energy] {{webarchive|url=https://web.archive.org/web/20130516003736/http://www.bp.com/sectiongenericarticle800.do?categoryId=9037130&contentId=7068669 |date=2013-05-16}}, Workbook (xlsx), London, 2012</ref>]]
|}

==Energy consumption by power source==
[[File:Greenhouse Gas Emissions from Electricity Production IEA.PNG|right|thumb|"Hydropower-Internalised Costs and Externalised Benefits"; Frans H. Koch; [[International Energy Agency]] (IEA)-Implementing Agreement for Hydropower Technologies and Programmes; 2000.]]

To create lasting climate change mitigation, the replacement of high carbon [[emission intensity]] power sources, such as conventional [[fossil fuel]]s—[[oil]], [[coal]], and [[natural gas]]—with [[low-carbon power]] sources is required. Fossil fuels supply humanity with the vast majority of our energy demands, and at a growing rate. In 2012 the IEA noted that coal accounted for half the increased energy use of the prior decade, growing faster than all renewable energy sources.<ref>[http://www.iea.org/publications/freepublications/publication/English.pdf World energy outlook 2012 (IEA)]</ref> Both [[hydroelectricity]] and [[nuclear power]] together provide the majority of the generated [[low-carbon power]] fraction of global total power consumption.

{|class="wikitable" style="display: inline-block;"
|-
|style="width:120pt;" rowspan="2" | '''Fuel type'''
|colspan=3 | '''Average total global [[power (physics)|power]] consumption in [[terawatt|TW]]'''<ref>[http://www.eia.doe.gov/pub/international/iealf/table18.xls World Consumption of Primary Energy by Energy Type and Selected Country Groups] {{webarchive|url=https://web.archive.org/web/20061109125803/http://www.eia.doe.gov/pub/international/iealf/table18.xls |date=2006-11-09}} 31 December 2008 [[Microsoft Excel]] file format</ref>
|-
|'''1980'''
|'''2004'''
|'''2006'''
|-
| Oil || 4.38 || 5.58 || 5.74
|-
| Gas || 1.80 || 3.45 || 3.61
|-
| Coal || 2.34 || 3.87 || 4.27
|-
| [[Hydroelectric]] || 0.60 || 0.93 || 1.00
|-
| [[Nuclear power]] || 0.25 || 0.91 || 0.93
|-
| [[Geothermal]], [[wind power|wind]],<br/>[[solar energy]], wood || 0.02 || 0.13 || 0.16
|-
| '''Total''' || '''9.48''' || '''15.0''' || '''15.8'''
|-
| style="text-align:left;" colspan="4"| <small> Source: The USA [[Energy Information Administration]] </small>
|}<!-- The figures in this table are equivalent to those given in the EIA report.-->

{| class="wikitable"
! colspan="5" style="text-align:center; background:#cfb;"|Change and use of energy, by source, in units of ([[PWh]]) in that year.<ref>Eenergiläget in Sweden 2011 figure 49 and 53</ref>
|-
! style="background:#cfb;"|
! style="background:#cfb;"| Fossil
! style="background:#cfb;"| Nuclear
! style="background:#cfb;"| All renewables
! style="background:#cfb;"| Total
|-
| style="text-align:left;"| 1990 || style="text-align:right;"| 83.374 || style="text-align:right;"| 6.113 || style="text-align:right;"| 13.082 || style="text-align:right;"| 102.569
|-
| style="text-align:left;"| 2000 || style="text-align:right;"| 94.493 || style="text-align:right;"| 7.857 || style="text-align:right;"| 15.337 || style="text-align:right;"| 117.687
|-
| style="text-align:left;"| 2008 || style="text-align:right;"| 117.076 || style="text-align:right;"| 8.283 || style="text-align:right;"| 18.492 || style="text-align:right;"| 143.851
|-
| style="text-align:left;"| Change 2000–2008 || style="text-align:right;"| 22.583 || style="text-align:right;"| 0.426 || style="text-align:right;"| 3.155 || style="text-align:right;"| 26.164
|}

==Methods and means==
{{See also|Emission intensity}}
[[File:Projected global primary electricity consumption by source, over the 21st century, for a climate change mitigation scenario.png|thumb|alt=Refer to caption and image description|This graph shows the projected contribution of various energy sources to world primary electricity consumption (PEC).<ref>Figure 4.10, in: Chapter 4: Stabilization Scenarios, in {{harvnb|Clarke|others|2007|p=103}}</ref> It is based on a climate change mitigation scenario, in which GHG emissions are substantially reduced over the 21st century. In the scenario, emission reductions are achieved using a portfolio of energy sources, as well as reductions in energy demand. ''Also available in [[:File:Projected global primary electricity consumption by source, over the 21st century, for a climate change mitigation scenario (greyscale).png|greyscale]].'']]
Assessments often suggest that GHG emissions can be reduced using a portfolio of low-carbon technologies.<ref>{{citation
|chapter=Sec 5.5 Technology flows and development
|title=Climate Change 2007: Synthesis Report
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/syr/en/mains5-5.html
}}, in {{harvnb|IPCC AR4 SYR|2007}}</ref> At the core of most proposals is the reduction of [[greenhouse gas]] (GHG) emissions through reducing energy waste and switching to [[low-carbon power]] sources of energy. As the cost of reducing GHG emissions in the [[electricity]] sector appears to be lower than in other sectors, such as in the [[transportation]] sector, the electricity sector may deliver the largest proportional carbon reductions under an economically efficient climate policy.<ref name=issues>[http://www.issues.org/23.3/apt.html Issues in Science] & Technology Online; "Promoting Low-Carbon Electricity Production"</ref>

"Economic tools can be useful in designing climate change mitigation policies." "While the limitations of economics and social welfare analysis, including cost–benefit analysis, are widely documented, economics nevertheless provides useful tools for assessing the pros and cons of taking, or not taking, action on climate change mitigation, as well as of adaptation measures, in achieving competing societal goals. Understanding these pros and cons can help in making policy decisions on climate change mitigation and can influence the actions taken by countries, institutions and individuals."<ref name="AR5-WG3-Chap3"/>

Other frequently discussed means include [[energy conservation]], increasing [[fuel economy in automobiles]] (which includes the use of [[hybrid vehicle|electric hybrids]]), charging [[plug-in hybrid]]s and [[electric car]]s by [[low-carbon power|low-carbon electricity]], making [[individual and political action on climate change|individual-lifestyle changes]]<ref>{{citation
|chapter=Sec 4.3 Mitigation options
|title=Climate Change 2007: Synthesis Report
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/syr/en/mains4-3.html
}}, in {{harvnb|IPCC AR4 SYR|2007}}</ref> (e.g., [[cycling]] instead of [[driving]]),<ref>{{citation
|title=Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|chapter=Ch 5: Transport and its infrastructure
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch5.html
|author=Kahn Ribeiro, S.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch5s5-3-1-5.html Non-motorized transport (NMT), in: Sec 5.3.1.5 Road transport: mode shifts]
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007}}</ref> and [[business action on climate change|changing business practices]]. Many fossil fuel driven vehicles can be converted to use electricity, the US has the potential to supply electricity for 73% of light duty vehicles (LDV), using overnight charging. The US average CO2 emissions for a battery-electric car is 180 grams per mile vs 430 grams per mile for a gasoline car.<ref>http://www.fueleconomy.gov/feg/Find.do?zipCode=12345&year=2016&vehicleId=37067&action=bt3</ref> The emissions would be displaced away from street level, where they have "high human-health implications. Increased use of electricity "generation for meeting the future transportation load is primarily fossil-fuel based", mostly natural gas, followed by coal,<ref>{{cite web|publisher=Pacific Northwest National Laboratory|url=http://energyenvironment.pnnl.gov/ei/pdf/Impact%20Assessment%20of%20PHEV%20on%20US%20Power%20Grid.pdf|title=Impacts assessment of plug-in hybrid vehicles on electric utilities and regional u.s. power grids|year=2010}}</ref> but could also be met through nuclear, tidal, hydroelectric and other sources.

A range of energy technologies may contribute to climate change mitigation.<ref>{{citation
|chapter=Table 4.2, in: Sec 4.3 Mitigation options
|title=Climate Change 2007: Synthesis Report
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/syr/en/mains4-3.html
}}, in {{harvnb|IPCC AR4 SYR|2007}}</ref> These include [[nuclear power]] and [[renewable energy]] sources such as [[Biomass preprocessing|biomass]], [[hydroelectricity]], [[wind power]], [[solar power]], [[geothermal power]], [[ocean energy]], and; the use of [[carbon sink]]s, and [[carbon capture and storage]]. For example, [[Stephen W. Pacala|Pacala]] and [[Robert H. Socolow|Socolow]] of Princeton<ref name=pacala2004sws>{{cite journal
|title=Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies
|url=http://carbonsequestration.us/Papers-presentations/htm/Pacala-Socolow-ScienceMag-Aug2004.pdf
|first1=Stephen|last1=Pacala|author1-link=
|first2=Robert H.|last2=Socolow|author2-link=
|journal=[[Science (journal)|Science]]
|volume=305 |issue=5686|pages=968–72|year=2004
|doi=10.1126/science.1100103
|pmid=15310891|bibcode= 2004Sci...305..968P}}<br/>See also:
{{cite web
|title=Stabwedge
|url=http://www.princeton.edu/~cmi/resources/stabwedge.htm
|publisher=CMI (Carbon Mitigation Initiative) at [[Princeton University]]
|quote=Resources for Pacala & Socolow(2004)}}</ref> have proposed a 15 part program to reduce CO<sub>2</sub> emissions by 1 billion metric tons per year − or 25 billion tons over the 50-year period using today's technologies as a type of [[global warming game]].<ref>{{cite web
|url= http://www.nature.com/climate/2008/0807/full/climate.2008.59.html
|title=Cleaning up on carbon
|first= Joe
|last= Romm
|work=Nature Reports Climate Change
|date= 19 June 2008
|accessdate=2 January 2013}}</ref>

Another consideration is how future [[socioeconomic development]] proceeds. Development choices (or "pathways") can lead differences in GHG emissions.<ref>{{citation
|title=Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
|chapter=Ch 12: Sustainable Development and mitigation
|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch12.html
|author=Sathaye, J.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch12s12-2-1-1.html Sec 12.2.1.1 Development paths as well as climate policies determine GHG emissions]
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007|pp=701–703}}</ref> Political and social attitudes may affect how easy or difficult it is to implement effective policies to reduce emissions.<ref>{{citation
|title=Climate Change 2001: Working Group III: Mitigation
|chapter=Ch 2. Greenhouse Gas Emission Mitigation Scenarios and Implications
|chapter-url=http://www.grida.no/climate/ipcc_tar/wg3/068.htm
|author=Morita, T.
|at=[http://www.grida.no/climate/ipcc_tar/wg3/082.htm Sec 2.5.2.2 Storylines of Post-SRES Mitigation Scenarios]
|display-authors=etal}}, in {{harvnb|IPCC TAR WG3|2001|pp=149–150}}</ref>

===Demand side management===

====Lifestyle and behavior====
The [[IPCC]] [[IPCC Fifth Assessment Report|Fifth Assessment Report]] emphasises that behaviour, lifestyle, and cultural change have a high mitigation potential in some sectors, particularly when complementing technological and structural change.<ref name="edenhofer-etal-2014">{{cite book
|first1= Ottmar | last1= Edenhofer
|first2= Ramón | last2= Pichs-Madruga
|display-authors= etal
|editor= IPCC
|year= 2014
|title= Climate change 2014: mitigation of climate change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
|chapter= Summary for Policymakers
|publisher= [[Cambridge University Press]]
|place= Cambridge, UK and New York, NY, USA
|isbn= 978-1-107-65481-5
|url= http://www.ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_full.pdf
|access-date= 2016-06-21
}}</ref>{{rp|20}}
In general, higher consumption lifestyles have a greater environmental impact. Several scientific studies have shown that when people, especially those living in [[developed country|developed countries]] but more generally including all countries, wish to reduce their carbon footprint, there are four key "high-impact" actions they can take:<ref name=Wynes-Nicholas-2017>{{cite journal |url= http://iopscience.iop.org/article/10.1088/1748-9326/aa7541 |title= The climate mitigation gap: education and government recommendations miss the most effective individual actions |journal= Environmental Research Letters |first1= Seth |last1= Wynes |first2= Kimberly A |last2= Nicholas |date= 12 July 2017 |publisher= Environmental Research Letters |volume= 12 |page= 074024 |number= 7 |doi= 10.1088/1748-9326/aa7541 |bibcode= 2017ERL....12g4024W}}</ref><ref name=Ceballos-Ehrlich-2017-05>{{cite journal |last1=Ceballos|first1=Gerardo|last2=Ehrlich|first2=Paul P |last3=Dirzo|first3=Rodolfo|date=23 May 2017|title=Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines|url=http://www.pnas.org/content/early/2017/07/05/1704949114.full|journal=[[Proceedings of the National Academy of Sciences of the United States of America]]|quote=Much less frequently mentioned are, however, the ultimate drivers of those immediate causes of biotic destruction, namely, human overpopulation and continued population growth, and overconsumption, especially by the rich. These drivers, all of which trace to the fiction that perpetual growth can occur on a finite planet, are themselves increasing rapidly.|doi=10.1073/pnas.1704949114|page=201704949}}</ref><ref name="PimmJenkins">{{cite journal |last1=Pimm |first1=S. L. |last2=Jenkins |first2=C. N. |last3=Abell |first3=R. |last4=Brooks|first4=T. M. |last5= Gittleman|first5=J. L. |last6= Joppa |first6=L. N. |last7=Raven|first7=P. H. |last8=Roberts |first8=C. M.|last9= Sexton |first9=J. O.|date=30 May 2014 |title=The biodiversity of species and their rates of extinction, distribution, and protection |url=http://static.squarespace.com/static/51b078a6e4b0e8d244dd9620/t/538797c3e4b07a163543ea0f/1401395139381/Pimm+et+al.+2014.pdf|journal= [[Science (journal)|Science]] |volume= 344|issue=6187|page= 1246752|doi=10.1126/science.1246752 |access-date= 15 December 2016|quote=The overarching driver of species extinction is human population growth and increasing per capita consumption. |pmid=24876501}}</ref>

:1. [[Human overpopulation|Not having]] an additional child (58.6 tonnes CO<sub>2</sub>-equivalent emission reductions per year)

:2. Living [[car-free movement|car-free]] (2.4 tonnes CO<sub>2</sub>)

:3. Avoiding one round-trip transatlantic flight (1.6 tonnes)

:4. Eating a [[plant-based diet]] (0.8 tonnes)

These appear to differ significantly from the popular advice for “greening” one's lifestyle, which seem to fall mostly into the “low-impact” category: Replacing a typical car with a hybrid (0.52 tonnes); Washing clothes in cold water (0.25 tonnes); Recycling (0.21 tonnes); Upgrading light bulbs (0.10 tonnes); etc. The researchers found that public discourse on reducing one's carbon footprint overwhelmingly focuses on low-impact behaviors, and that mention of the high-impact behaviors is almost non-existent in the mainstream media, government publications, K-12 school textbooks, etc.<ref name=Wynes-Nicholas-2017/><ref name=Ceballos-Ehrlich-2017-05/><ref name="PimmJenkins"/>

The researchers added that “Our recommended high-impact actions are more effective than many more commonly discussed options (e.g. eating a plant-based diet saves eight times more emissions than upgrading light bulbs). More significantly, a US family who chooses to have one fewer child would provide the same level of emissions reductions as 684 teenagers who choose to adopt comprehensive recycling for the rest of their lives.”<ref name=Wynes-Nicholas-2017/><ref name=Ceballos-Ehrlich-2017-05/><ref name="PimmJenkins"/>

=====Dietary change=====
{{See also|Low-carbon diet}}

Overall, food accounts for the largest share of consumption-based GHG emissions with nearly 20% of the global carbon footprint, followed by housing, mobility, services, manufactured products, and construction. Food and services are more significant in poor countries, while mobility and manufactured goods are more significant in rich countries.<ref name="fleurbaey-etal-2014">{{cite book
|first1= Marc | last1= Fleurbaey
|first2= Sivan | last2= Kartha
|display-authors= etal
|editor= IPCC
|year= 2014
|title= Climate change 2014: mitigation of climate change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
|chapter= Chapter 4: Sustainable Development and Equity
|publisher= [[Cambridge University Press]]
|place= Cambridge, UK and New York, NY, USA
|isbn= 978-1-107-65481-5
|url= http://www.ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_full.pdf
|access-date= 2016-06-21
}}</ref>{{rp|327}} A 2014 study into the real-life diets of British people estimates their greenhouse gas contributions ([[carbon dioxide equivalent|{{CO2}}eq]]) to be: 7.19{{nbsp}}kg/day for high meat-eaters through to 3.81{{nbsp}}kg/day for vegetarians and 2.89{{nbsp}}kg/day for vegans.<ref name="scarborough-etal-2014">{{cite journal
|first1= Peter | last1= Scarborough
|first2= Paul N. | last2= Appleby
|first3= Anja | last3= Mizdrak
|first4= Adam D.M. | last4= Briggs
|first5= Ruth C. | last5= Travis
|first6= Kathryn E. | last6= Bradbury
|first7= Timothy J. | last7= Key
|title= Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK
|journal= Climatic Change
|date= July 2014
|volume= 125
|number= 2
|pages= 179–92
|doi= 10.1007/s10584-014-1169-1
|pmid= 25834298
|url= https://link.springer.com/article/10.1007/s10584-014-1169-1
|pmc=4372775
}}</ref>
The widespread adoption of a vegetarian diet could cut food-related greenhouse gas emissions by 63% by 2050.<ref name="harvey-2016">{{cite news
|last1= Harvey | first1= Fiona
|title= Eat less meat to avoid dangerous global warming, scientists say
|url= https://www.theguardian.com/environment/2016/mar/21/eat-less-meat-vegetarianism-dangerous-global-warming
|access-date= 2016-06-20
|work= The Guardian
|date= 21 March 2016
}}</ref>
China introduced new dietary guidelines in 2016 which aim to cut meat consumption by 50% and thereby reduce greenhouse gas emissions by 1{{nbsp}}billion tonnes by 2030.<ref name="milman-2016">{{cite news
|last1= Milman | first1= Oliver
|title= China's plan to cut meat consumption by 50% cheered by climate campaigners
|url= https://www.theguardian.com/world/2016/jun/20/chinas-meat-consumption-climate-change
|access-date= 2016-06-20
|work= The Guardian
|date= 20 June 2016
}}</ref> A 2016 study concluded that taxes on meat and milk could simultaneously result in reduced greenhouse gas emissions and healthier diets. The study analyzed surcharges of 40% on beef and 20% on milk and suggests that an optimum plan would reduce emissions by 1{{nbsp}}billion tonnes per year.<ref name="carrington-2016">{{cite news
|last= Carrington | first= Damian
|title= Tax meat and dairy to cut emissions and save lives, study urges
|date= 7 November 2016
|work= The Guardian
|location= London, United Kingdom
|issn= 0261-3077
|url= https://www.theguardian.com/environment/2016/nov/07/tax-meat-and-dairy-to-cut-emissions-and-save-lives-study-urges
|access-date= 2016-11-07
}}</ref><ref name="springmann-etal-2016">{{cite journal
|last1= Springmann | first1= Marco
|last2= Mason-D'Croz | first2= Daniel
|last3= Robinson | first3= Sherman
|last4= Wiebe | first4= Keith
|last5= Godfray | first5= H Charles J
|last6= Rayner | first6= Mike
|last7= Scarborough | first7= Peter
|title= Mitigation potential and global health impacts from emissions pricing of food commodities
|date= 7 November 2016
|journal= Nature Climate Change
|volume =7
|page =69
|doi= 10.1038/nclimate3155
|issn= 1758-678X
|bibcode= 2017NatCC...7...69S}}</ref>

====Energy efficiency and conservation====
{{Main|Efficient energy use|Energy conservation}}
[[File:Led-lampa.jpg|thumb|A 230-volt LED light bulb, with an [[Edison screw|E27]] base (10 [[watt]]s, 806 [[lumen (unit)|lumen]]s).]]

Efficient energy use, sometimes simply called "energy efficiency", is the goal of efforts to reduce the amount of energy required to provide products and services. For example, [[building insulation|insulating a home]] allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature. Installing [[LED lamp|LED lighting]], [[fluorescent lamp|fluorescent lighting]], or natural [[skylight|skylight windows]] reduces the amount of energy required to attain the same level of illumination compared to using traditional [[incandescent light bulb]]s. [[Compact fluorescent lamp]]s use only 33% of the energy and may last 6 to 10 times longer than incandescent lights.<ref>[[Mark Diesendorf|Diesendorf, Mark]] (2007). ''[[Greenhouse Solutions with Sustainable Energy]]'', UNSW Press, p. 86.</ref> LED lamps use only about 10% of the energy an incandescent lamp requires.

Energy efficiency has proved to be a cost-effective strategy for building economies without necessarily growing [[world energy resources and consumption|energy consumption]]. For example, the state of [[California]] began implementing energy-efficiency measures in the mid-1970s, including building code and appliance standards with strict efficiency requirements. During the following years, California's energy consumption has remained approximately flat on a per capita basis while national US consumption doubled. As part of its strategy, California implemented a "loading order" for new energy resources that puts energy efficiency first, renewable electricity supplies second, and new fossil-fired power plants last.<ref>{{cite web|url=http://www.energy.ca.gov/2005publications/CEC-400-2005-043/CEC-400-2005-043.PDF |title=Loading Order White Paper |format=PDF |date= |accessdate=2010-07-16}}</ref>

[[Energy conservation]] is broader than energy efficiency in that it encompasses using less energy to achieve a lesser energy demanding service, for example through behavioral change, as well as encompassing energy efficiency. Examples of conservation without efficiency improvements would be heating a room less in winter, driving less, or working in a less brightly lit room. As with other definitions, the boundary between efficient energy use and energy conservation can be fuzzy, but both are important in environmental and economic terms. This is especially the case when actions are directed at the saving of fossil fuels.<ref>Diesendorf, Mark (2007). ''Greenhouse Solutions with Sustainable Energy'', UNSW Press, p. 87.</ref>

Reducing energy use is seen as a key solution to the problem of reducing greenhouse gas emissions. According to the [[International Energy Agency]], improved energy efficiency in [[energy-efficient buildings|buildings]], industrial processes and [[sustainable transportation|transportation]] could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.<ref>{{cite web|author=Sophie Hebden |url=http://www.scidev.net/News/index.cfm?fuseaction=readNews&itemid=2929&language=1 |title=Invest in clean technology says IEA report |publisher=Scidev.net |date=2006-06-22 |accessdate=2010-07-16}}</ref>

====Demand-side switching sources====
Fuel switching on the demand side refers to changing the type of fuel used to satisfy a need for an energy service. To meet deep decarbonization goals, like the 80% reduction by 2050 goal being discussed in California and the European Union, many primary energy changes are needed.<ref>{{cite web |title=Climate Change |publisher=California Air Resources Board |accessdate=2015-04-29 |url=http://www.arb.ca.gov/cc/cc.htm}}</ref><ref>{{cite web |title= Roadmap for moving to a low-carbon economy in 2050 – European Commission |accessdate= 2015-04-29 |url= http://ec.europa.eu/clima/policies/roadmap/index_en.htm}}</ref> Energy efficiency alone may not be sufficient to meet these goals, switching fuels used on the demand side will help lower carbon emissions.<ref>{{cite journal |doi= 10.1088/1748-9326/8/1/014038 |issn= 1748-9326 |volume= 8 |issue= 1 |page= 014038 |last1= Wei |first1= Max |last2= Nelson |first2= James H |last3= Greenblatt |first3= Jeffery B |last4= Mileva |first4= Ana |last5= Johnston |first5= Josiah |last6= Ting |first6= Michael |last7= Yang |first7= Christopher |last8= Jones |first8= Chris |last9= McMahon |first9= James E |last10= Kammen |first10= Daniel M |title= Deep carbon reductions in California require electrification and integration across economic sectors |journal= Environmental Research Letters |accessdate= 2015-03-21 |date= 2013-03-01 |url= http://stacks.iop.org/1748-9326/8/i=1/a=014038?key=crossref.37ef0d9dff3c11bf4c176aa87e4f5831|bibcode= 2013ERL.....8a4038W}}</ref><ref>{{cite journal |last= Williams |first= James H. |title= The technology path to deep greenhouse gas emissions cuts by 2050: The pivotal role of electricity |journal= Science |volume= 335 |issue= 6064 |page= 53 |accessdate= 2015-03-21 |date= 2012 |url= https://escholarship.org/uc/item/2mz2472z.pdf |bibcode= 2012Sci...335...53W |doi= 10.1126/science.1208365}}</ref> Progressively coal, oil and eventually natural gas for space and water heating in buildings will need to be reduced. For an equivalent amount of heat, burning natural gas produces about 45 per cent less carbon dioxide than burning [[coal]].<ref name=gasdotorg>{{cite web |url=http://www.naturalgas.org/environment/naturalgas.asp#greenhouse/ |title=Natural Gas and the Environment |publisher=Naturalgas.org |date= |accessdate=2011-02-06 |deadurl=yes |archiveurl=https://web.archive.org/web/20090503132200/http://www.naturalgas.org/environment/naturalgas.asp#greenhouse/ |archivedate=2009-05-03 |df=}}</ref> There are various ways in which this could happen, and different strategies will likely make sense in different locations. While the system efficiency of a gas furnace may be higher than the combination of natural gas power plant and electric heat, the combination of the same natural gas power plant and an electric [[heat pump]] has lower emissions per unit of heat delivered in all but the coldest climates. This is possible because of the very efficient [[coefficient of performance]] of heat pumps.

At the beginning of this century 70% of all electricity was generated by fossil fuels, and as carbon free sources eventually make up half of the generation mix, replacing gas or oil furnaces and water heaters with electric ones will have a climate benefit. In areas like Norway, [[Brazil]], and [[Quebec]] that have abundant hydroelectricity, electric heat and hot water are common.

The economics of switching the demand side from fossil fuels to electricity for heating, will depend on the price of fuels vs electricity and the relative prices of the equipment. The EIA Annual Energy Outlook 2014 suggests that domestic gas prices will rise faster than electricity prices which will encourage electrification in the coming decades.<ref>{{cite web|url=http://www.eia.gov/forecasts/aeo/ |title=Annual Energy Outlook 2015 – Energy Information Administration |publisher=Eia.gov |date=2015-04-14 |accessdate=2016-05-06}}</ref>
Electrifying heating loads may also provide a flexible resource that can participate in [[demand response]]. Since thermostatically controlled loads have inherent energy storage, electrification of heating could provide a valuable resource to integrate variable renewable resources into the grid.

Alternatives to electrification, include decarbonizing pipeline gas through [[power to gas]], [[biogas]], or other [[carbon-neutral fuels]]. A 2015 study by Energy+Environmental Economics shows that a hybrid approach of decarbonizing pipeline gas, electrification, and energy efficiency can meet carbon reduction goals at a similar cost as only electrification and energy efficiency in Southern California.<ref>{{Citation |title= E3 Decarbonizing Pipeline 01-27-2015.pdf |accessdate= 2015-04-14 |url= https://ethree.com/documents/E3_Decarbonizing_Pipeline_01-27-2015.pdf}}</ref>

====Demand side grid management====
Expanding intermittent electrical sources such as [[wind power]], creates a growing problem balancing grid fluctuations. Some of the plans include building pumped storage or continental [[super grid]]s costing billions of dollars. However instead of building for more power, there are a variety of ways to affect the size and timing of electricity demand on the consumer side. Designing for reduced demands on a smaller power grid is more efficient and economic than having extra generation and transmission for intermittentcy, power failures and peak demands. Having these abilities is one of the chief aims of a [[smart grid]].

[[Net energy metering#Time of use metering|Time of use]] metering is a common way to motivate electricity users to reduce their peak load consumption. For instance, running dishwashers and laundry at night after the peak has passed, reduces electricity costs.

[[Dynamic demand]] plans have devices passively shut off when stress is sensed on the electrical grid. This method may work very well with thermostats, when power on the grid sags a small amount, a low power temperature setting is automatically selected reducing the load on the grid. For instance millions of refrigerators reduce their consumption when clouds pass over solar installations. Consumers would need to have a [[smart meter]] in order for the utility to calculate credits.

[[Demand response]] devices could receive all sorts of messages from the grid. The message could be a request to use a low power mode similar to dynamic demand, to shut off entirely during a sudden failure on the grid, or notifications about the current and expected prices for power. This would allow electric cars to recharge at the least expensive rates independent of the time of day. The [[vehicle-to-grid]] suggestion would use a car's battery or fuel cell to supply the grid temporarily.

===Alternative energy sources===

====Renewable energy====
{{Main|Renewable energy|Renewable energy commercialization|Renewable energy debate}}

[[File:Bp world energy consumption 2016.gif|thumb|The worldwide growth of renewable energy is shown by the green line<ref>[http://www.bp.com/statisticalreview Statistical Review of World Energy], Workbook (xlsx), London, 2016</ref>]] [[File:ThreeGorgesDam-China2009.jpg|thumb |The 22,500 [[megawatt|MW]] [[nameplate capacity]] [[Three Gorges Dam]] in the [[Peoples Republic of China]], the largest hydroelectric power station in the world.]]
[[File:Shepherds Flat Wind Farm 2011.jpg|thumb |The [[Shepherds Flat Wind Farm]] is an 845 [[megawatt]] (MW) [[nameplate capacity]], [[wind farm]] in the US state of [[Oregon]], each turbine is a nameplate 2 or 2.5 MW electricity generator.]]
[[File:12-05-08 AS1.JPG|thumb|right|The 150 MW [[Andasol solar power station]] is a commercial [[parabolic trough]] [[solar thermal]] power plant, located in [[Renewable energy in Spain|Spain]]. The Andasol plant uses tanks of molten salt to store solar energy so that it can continue generating electricity for 7.5 hours after the sun has stopped shining.<ref>{{cite web |url= |title=Saving for a rainy day |author=Edwin Cartlidge |date=18 November 2011 |work=Science (Vol 334) |pages=922–24}}</ref>]]
[[File:Solar-Panel-Cooker-in-front-of-hut.jpg|thumb |[[Solar cooker]]s use sunlight as energy source for outdoor cooking.]]
Renewable energy flows involve natural phenomena such as [[sunlight]], [[wind]], rain, [[tide]]s, [[biomass|plant growth]], and [[geothermal heating|geothermal heat]], as the [[International Energy Agency]] explains:<ref>IEA Renewable Energy Working Party (2002). ''Renewable Energy... into the mainstream'', p. 9.</ref>
{{quote|Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, [[hydropower]], biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources.}}

[[Global warming|Climate change concerns]]<ref name=Stern>HM Treasury (2006). ''Stern Review on the Economics of Climate Change''.</ref><ref name=ieapress>International Energy Agency. [http://www.iea.org/Textbase/press/pressdetail.asp?PRESS_REL_ID=271 IEA urges governments to adopt effective policies based on key design principles to accelerate the exploitation of the large potential for renewable energy] 29 September 2008.</ref><ref name=UNEP2>[[REN21]] (2006). [http://www.risoe.dk/rispubl/art/2006_120_report.pdf ''Changing climates: The Role of Renewable Energy in a Carbon-constrained World'' (PDF)] {{webarchive|url=https://web.archive.org/web/20070611182411/http://www.risoe.dk/rispubl/art/2006_120_report.pdf |date=2007-06-11}} p. 2.</ref> and the need to reduce carbon emissions are driving increasing growth in the [[renewable energy industry|renewable energy industries]].<ref name=UNnews>[https://www.un.org/apps/news/story.asp?NewsID=24982&Cr=climate New UN report points to power of renewable energy to mitigate carbon emissions] ''UN News Centre'', 8 December 2007.</ref><ref name=mak>[[Joel Makower]], [[Ron Pernick]], and [[Clint Wilder]] (2008). [http://www.cleanedge.com/reports/pdf/Trends2008.pdf ''Clean Energy Trends 2008]'', [[Clean Edge]], p. 2.</ref><ref name="UNEP">United Nations Environment Programme and New Energy Finance Ltd. (2007). [http://sefi.unep.org/fileadmin/media/sefi/docs/publications/SEFI_Investment_Report_2007.pdf ''Global Trends in Sustainable Energy Investment 2007: Analysis of Trends and Issues in the Financing of Renewable Energy and Energy Efficiency in OECD and Developing Countries'' (PDF)] {{webarchive|url=https://web.archive.org/web/20090325060117/http://sefi.unep.org/fileadmin/media/sefi/docs/publications/SEFI_Investment_Report_2007.pdf |date=2009-03-25}} p. 3.</ref> Low-carbon renewable energy replaces conventional fossil fuels in three main areas: [[power generation]], [[solar hot water|hot water]]/ [[space heating]], and [[transport fuel]]s.<ref name=ren15>[[REN21]] (2010). [http://www.ren21.net/globalstatusreport/REN21_GSR_2010_full.pdf Renewables 2010 Global Status Report] {{webarchive|url=https://web.archive.org/web/20120513043047/http://www.ren21.net/globalstatusreport/REN21_GSR_2010_full.pdf |date=2012-05-13}} p. 15.</ref> In 2011, the share of renewables in [[electricity generation]] worldwide grew for the fourth year in a row to 20.2%.<ref>{{cite web|title=Conclusion|url=http://www.energies-renouvelables.org/observ-er/html/inventaire/Eng/conclusion.asp|work=Worldwide electricity production from renewable energy sources|publisher=Observ'ER|accessdate=28 March 2013|location=Paris|year=2012}}</ref> Based on [[REN21]]'s 2014 report, renewables contributed 19% to supply global energy consumption. This energy consumption is divided as 9% coming from burning biomass, 4.2% as heat energy (non-biomass), 3.8% hydro electricity and 2% as electricity from wind, solar, geothermal, and biomass thermal power plants.<ref>http://www.ren21.net/Portals/0/documents/Resources/GSR/2014/GSR2014_full%20report_low%20res.pdf</ref>

[[Renewable energy commercialization|Renewable energy use]] has grown much faster than anyone anticipated.<ref name=pg11>{{cite web |url=http://www.renewableenergyworld.com/rea/news/article/2013/04/100-percent-renewable-vision-building?amp;buffer_share=fdc06 |title=100 Percent Renewable Vision Building |author=Paul Gipe |date=4 April 2013 |work=Renewable Energy World}}</ref> The [[Intergovernmental Panel on Climate Change]] (IPCC) has said that there are few fundamental technological limits to integrating a portfolio of renewable energy technologies to meet most of total global energy demand.<ref name="IPCC 2011 17">{{cite web|url=http://srren.ipcc-wg3.de/report/IPCC_SRREN_SPM.pdf |title=Special Report on Renewable Energy Sources and Climate Change Mitigation |author=IPCC |year=2011 |work=Cambridge University Press, Cambridge, United Kingdom and New York, NY|page=17 |deadurl=yes |archiveurl=https://web.archive.org/web/20140111081913/http://srren.ipcc-wg3.de/report/IPCC_SRREN_SPM.pdf |archivedate=2014-01-11 |df=}}</ref> At the national level, at least 30 nations around the world already have renewable energy contributing more than 20% of energy supply.

As of 2012, renewable energy accounts for almost half of new electricity capacity installed and costs are continuing to fall.<ref name=irena111>{{cite web |url=http://www.irena.org/DocumentDownloads/Publications/Overview_Renewable%20Power%20Generation%20Costs%20in%202012.pdf |title=Renewable Power Generation Costs in 2012: An Overview |author=International Renewable Energy Agency |year=2012 |work=}}</ref> [[Public policy]] and political leadership helps to "level the playing field" and drive the wider acceptance of renewable energy technologies.<ref name="renewableenergyfocus.com">Donald W. Aitken. [http://www.renewableenergyfocus.com/download/165 Transitioning to a Renewable Energy Future], [[International Solar Energy Society]], January 2010, p. 3.</ref> {{As of|2011}}, 118 countries have targets for their own renewable energy futures, and have enacted wide-ranging [[public policies]] to promote renewables.<ref name="map.ren21.net">REN21 (2012). [http://www.map.ren21.net/GSR/GSR2012.pdf Renewables Global Status Report 2012] {{webarchive |url=https://web.archive.org/web/20121215215616/http://www.map.ren21.net/GSR/GSR2012.pdf |date=December 15, 2012}} p. 17.</ref><ref name=ren212011>{{cite web|url=http://www.ren21.net/Portals/97/documents/GSR/GSR2011_Master18.pdf |title=Renewables 2011: Global Status Report |author=[[REN21]] |year=2011 |pages=11–13 |deadurl=yes |archiveurl=https://web.archive.org/web/20110905003859/http://www.ren21.net/Portals/97/documents/GSR/GSR2011_Master18.pdf |archivedate=2011-09-05 |df=}}</ref> Leading renewable energy companies include [[BrightSource Energy]], [[First Solar]], [[Gamesa Corporación Tecnológica|Gamesa]], [[GE Energy]], [[Goldwind]], [[Sinovel]], [[Suntech]], [[Trina Solar]], [[Vestas]], and [[Yingli]].<ref name=top>Top of the list, ''Renewable Energy World'', 2 January 2006.</ref><ref name=keith>Keith Johnson, [https://blogs.wsj.com/environmentalcapital/2009/03/25/wind-shear-ge-wins-vestas-loses-in-wind-power-market-race/ Wind Shear: GE Wins, Vestas Loses in Wind-Power Market Race], ''Wall Street Journal'', March 25th 2009, accessed on January 7th 2010.</ref>

The incentive to use [[100% renewable energy]] has been created by [[global warming]] and other ecological as well as economic concerns.<ref name=pg11/> [[Mark Z. Jacobson]] says producing all new energy with [[wind power]], [[solar power]], and [[hydropower]] by 2030 is feasible and existing energy supply arrangements could be replaced by 2050. Barriers to implementing the renewable energy plan are seen to be "primarily social and political, not technological or economic". Jacobson says that energy costs with a wind, solar, water system should be similar to today's energy costs.<ref name=enpol2011>{{cite web |url=http://www.stanford.edu/group/efmh/jacobson/Articles/I/DJEnPolicyPt2.pdf |title=Providing all global energy with wind, water, and solar power, Part II: Reliability, system and transmission costs, and policies |author1=Mark A. Delucchi |author2=Mark Z. Jacobson |date=2011 |volume=39 |work=Energy Policy |pages=1170–90 |publisher=Elsevier Ltd}}</ref> According to a 2011 projection by the (IEA)[[International Energy Agency]], solar power generators may produce most of the world's electricity within 50 years, dramatically reducing harmful greenhouse gas emissions.<ref name=ieaiea2011>{{cite news |url=https://www.bloomberg.com/news/2011-08-29/solar-may-produce-most-of-world-s-power-by-2060-iea-says.html |title=Solar May Produce Most of World's Power by 2060, IEA Says |author=Ben Sills |date= August 29, 2011 |work=Bloomberg}}</ref> Critics of the "100% renewable energy" approach include [[Vaclav Smil]] and [[James E. Hansen]]. Smil and Hansen are concerned about the [[variable renewable energy|variable output]] of solar and wind power, [[NIMBY]]ism, and a lack of infrastructure.<ref>{{cite web|last=Smil|first=Vaclav|title=A Skeptic Looks at Alternative Energy|url=http://spectrum.ieee.org/energy/renewables/a-skeptic-looks-at-alternative-energy/0|work=Spectrum magazine|publisher=IEEE|accessdate=28 March 2013|year=2012}}</ref>

Economic analysts expect market gains for [[renewable energy]] (and [[efficient energy use]]) following the [[2011 Japanese nuclear accidents]].<ref>{{cite web |url=http://www.upi.com/Science_News/Resource-Wars/2011/03/21/Japans-nuclear-disaster-boosts-renewables/UPI-28501300714143/#ixzz1HJPwVWKa |title= Japan's nuclear disaster boosts renewables |date=March 21, 2011 |work=UPI.com}}</ref><ref>{{cite news |url=https://www.theguardian.com/environment/2011/mar/15/japan-nuclear-explosion-energy-renewables |title=Japan nuclear crisis prompts surging investor confidence in renewables |author=John Vidall |date=15 March 2011 |work=The Guardian |location=London}}</ref> In his 2012 [[State of the Union]] address, President Barack Obama restated his commitment to renewable energy and mentioned the long-standing Interior Department commitment to permit 10,000 MW of renewable energy projects on public land in 2012.<ref name="Lindsay Morris">{{cite web |url=http://www.renewableenergyworld.com/rea/blog/post/2012/01/obama-sticking-to-promise-of-clean-energy |title=Obama: Sticking to "Promise of Clean Energy" |author=Lindsay Morris |date=25 January 2012 |work=Renewable Energy World}}</ref> Globally, there are an estimated 3 million direct jobs in renewable energy industries, with about half of them in the biofuels industry.<ref name=ren9>[[REN21]] (2010). [http://www.ren21.net/Portals/97/documents/GSR/REN21_GSR_2010_full_revised%20Sept2010.pdf Renewables 2010 Global Status Report] {{webarchive |url=https://web.archive.org/web/20120416031610/http://www.ren21.net/Portals/97/documents/GSR/REN21_GSR_2010_full_revised%20Sept2010.pdf |date=April 16, 2012}} pp. 9, 34.</ref>

Some countries, with favorable [[geography]], [[geology]], and [[weather]] well suited to an economical exploitation of renewable energy sources, already get most of their electricity from renewables, including from [[geothermal energy]] in Iceland (100 percent), and [[hydroelectric]] power in Brazil (85 percent), Austria (62 percent), New Zealand (65 percent), and Sweden (54 percent).<ref name=ren53>[[REN21]] (2010). [http://www.ren21.net/globalstatusreport/REN21_GSR_2010_full.pdf Renewables 2010 Global Status Report] {{webarchive|url=https://web.archive.org/web/20120513043047/http://www.ren21.net/globalstatusreport/REN21_GSR_2010_full.pdf |date=2012-05-13}} p. 53.</ref> Renewable power generators are spread across many countries, with wind power providing a significant share of electricity in some regional areas: for example, 14 percent in the US state of Iowa, 40 percent in the northern German state of Schleswig-Holstein, and 20 percent in Denmark. [[Solar water heating]] makes an important and growing contribution in many countries, most notably in China, which now has 70 percent of the global total (180 GWth). Worldwide, total installed solar water heating systems meet a portion of the water heating needs of over 70 million households. The use of [[biomass]] for heating continues to grow as well. In Sweden, national use of biomass energy has surpassed that of oil. Direct [[geothermal heating]] is also growing rapidly.<ref name=ren53/> Renewable [[biofuel]]s for transportation, such as [[ethanol fuel]] and [[biodiesel]], have contributed to a significant decline in oil consumption in the United States since 2006. The 93&nbsp;billion liters of biofuels produced worldwide in 2009 displaced the equivalent of an estimated 68&nbsp;billion liters of gasoline, equal to about 5 percent of world gasoline production.<ref name=ren53/>

{{Multiple image
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|width1= 225
|width2= 225
|image1=IvanpahRunning.JPG|link=Ivanpah Solar Power Facility
|image2=Topaz Solar Farm, California Valley.jpg
|footer=Some of the world's largest [[solar power]] stations: [[Ivanpah Solar Power Facility|Ivanpah]] (CSP) and [[Topaz Solar Farm|Topaz]] (PV), both in [[California]]
}}

====Nuclear power====
{{See also|Nuclear renaissance}}
[[File:Advanced Test Reactor.jpg|thumb|200px|left|Blue [[Cherenkov radiation|Cherenkov]] light being produced near the core of the Fission powered [[Advanced Test Reactor]]]]

Since about 2001 the term "nuclear renaissance" has been used to refer to a possible [[nuclear power]] industry revival, driven by rising [[price of petroleum|fossil fuel prices]] and new concerns about meeting [[greenhouse gas]] emission limits.<ref name="intro">{{cite web|url=http://www.world-nuclear.org/info/inf104.html|title=The Nuclear Renaissance – World Nuclear Association|publisher=}}</ref> However, in March 2011 the [[Fukushima nuclear disaster]] in Japan and associated shutdowns at [[2011 Japanese nuclear incidents|other nuclear facilities]] raised questions among some commentators over the future of nuclear power.<ref>[https://www.bloomberg.com/news/2011-03-13/nuclear-renaissance-threatened-as-japan-fights-meltdown-at-quake-hit-plant.html Nuclear Renaissance Threatened as Japan's Reactor Struggles] Bloomberg, published March 2011, accessed 2011-03-14</ref><ref>[https://www.reuters.com/article/2011/03/14/us-japan-quake-nuclear-analysis-idUSTRE72C41W20110314 Analysis: Nuclear renaissance could fizzle after Japan quake] Reuters, published 2011-03-14, accessed 2011-03-14</ref><ref>[https://www.reuters.com/article/2011/03/13/us-nuclear-usa-idUSTRE72C2UW20110313 Japan nuclear woes cast shadow over U.S. energy policy] Reuters, published 2011-03-13, accessed 2011-03-14</ref> [[Platts]] has reported that "the crisis at Japan's Fukushima nuclear plants has prompted leading energy-consuming countries to review the safety of their existing reactors and cast doubt on the speed and scale of planned expansions around the world".<ref>{{cite web |url=http://www.platts.com/RSSFeedDetailedNews/RSSFeed/ElectricPower/6925550 |title=NEWS ANALYSIS: Japan crisis puts global nuclear expansion in doubt |date=21 March 2011 |publisher=Platts}}</ref>

The [[World Nuclear Association]] has reported that nuclear electricity generation in 2012 was at its lowest level since 1999.<ref name=wna13>{{cite web |url=http://www.world-nuclear-news.org/NN_Nuclear_power_down_in_2012_2006131.html |title=Nuclear power down in 2012 |author=WNA |date=20 June 2013 |work=World Nuclear News}}</ref> Several previous international studies and assessments,<ref name="Sims, R.E.H., et al.">{{citation
|title=Climate Change 2007: Working Group III: Mitigation of Climate Change
|chapter=Ch. 4: Energy supply
|author=Sims, R.E.H.
|at=[http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch4s4-es.html Executive summary]
|display-authors=etal}}, in {{harvnb|IPCC AR4 WG3|2007}}</ref><ref name="IAEA 2008 42">{{harvnb|IAEA|2008|p=42}}</ref><ref>{{citation
|title=Technology Roadmap: Nuclear Energy. 2010 Edition
|date=16 June 2010
|author=IEA
|url=http://iea.org/publications/freepublications/publication/nuclear_roadmap.pdf
|publisher=Organization for Economic Co-operation and Development (OECD) / International Energy Agency (IEA) and OECD / Nuclear Energy Agency (NEA)
}}, pp. 5–6. Also available in [http://iea.org/publications/freepublications/publication/name,3906,en.html Chinese and Italian]</ref> suggested that as part of the portfolio of other [[low-carbon energy]] technologies, nuclear power will continue to play a role in reducing greenhouse gas emissions. Historically, nuclear power usage is estimated to have prevented the atmospheric emission of 64 giga[[tonne]]s of [[carbon dioxide equivalent|CO2-equivalent]] as of 2013.<ref>{{cite journal|url=https://dx.doi.org/10.1021/es3051197|title=Prevented Mortality and Greenhouse Gas Emissions from Historical and Projected Nuclear Power|first1=Pushker A.|last1=Kharecha|first2=James E.|last2=Hansen|date=7 May 2013|publisher=|journal=Environ. Sci. Technol.|volume=47|issue=9|pages=4889–95|doi=10.1021/es3051197|bibcode=2013EnST...47.4889K}}</ref> Public concerns about nuclear power include the [[spent nuclear fuel|fate of spent nuclear fuel]], [[nuclear accidents]], [[nuclear terrorism|security risks]], [[nuclear proliferation]], and [[economics of new nuclear power plants|a concern that nuclear power plants are very expensive]].<ref name=bm>[[Brian Martin (social scientist)|Brian Martin]]. [http://www.bmartin.cc/pubs/07sa.html Opposing nuclear power: past and present], ''Social Alternatives'', Vol. 26, No. 2, Second Quarter 2007, pp. 43–47.</ref><ref>{{cite web |url=http://bos.sagepub.com/content/67/4/43.abstract |title=Nuclear power and the public |author=[[M.V. Ramana]] |date=July 2011 |volume=67 |issue=4 |work=Bulletin of the Atomic Scientists |page=44}}</ref><ref>{{cite web |url=http://bos.sagepub.com/content/67/4/8.abstract |title=The implications of Fukushima: The US perspective |author=[[Mark Cooper (academic)|Mark Cooper]] |date=July 2011 |volume=67 |issue=4 |work=Bulletin of the Atomic Scientists |page=9}}</ref> Of these concerns, nuclear accidents and disposal of long-lived radioactive fuel/"waste" have probably had the greatest public impact worldwide.<ref name=bm/> Although generally unaware of it, both of these glaring public concerns are greatly diminished by present [[passive safety]] designs, the experimentally proven, "melt-down proof" [[EBR-II]], future [[molten salt reactor]]s, and the use of conventional and more advanced fuel/"waste" [[pyroprocessing]],<ref>[http://www.marklynas.org/2011/07/good-reasons-not-to-waste-nuclear-waste/ Good reasons not to waste nuclear 'waste'. Mark Lynas 2011]</ref> with the latter recycling or reprocessing not presently being commonplace as it is often considered to be cheaper to use a once-through [[nuclear fuel cycle]] in many countries, depending on the varying levels of intrinsic value given by a society in reducing the long-lived waste in their country, with France doing a considerable amount of reprocessing when compared to the US.<ref>{{cite web|url=http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-wastes/radioactive-waste-management.aspx|title=Radioactive Waste Management – Nuclear Waste Disposal |publisher=World Nuclear Association|date=2016|quote=A typical 1000 MWe light water reactor will generate (directly and indirectly) 200–350 m3 low- and intermediate-level waste per year. It will also discharge about 20 m3 (27 tonnes) of used fuel per year, which corresponds to a 75 m3 disposal volume following encapsulation if it is treated as waste. Where that used fuel is reprocessed, only 3 m3 of vitrified waste (glass) is produced, which is equivalent to a 28 m3 disposal volume following placement in a disposal canister.}}</ref><ref>{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0306454910000435|title=A comparative study on recycling spent fuels in gas-cooled fast reactors|first1=Hangbok|last1=Choi|first2=Alan|last2=Baxter|date=1 May 2010|publisher=|journal=Annals of Nuclear Energy|volume=37|issue=5|pages=723–729|doi=10.1016/j.anucene.2010.01.014}}</ref>

[[Nuclear power]], with a 10.6% share of world electricity production as of 2013, is second only to hydroelectricity as the largest source of low-carbon power.<ref>{{cite web|url=http://www.iea.org/publications/freepublications/publication/KeyWorld_Statistics_2015.pdf|title=Publication: Key World Energy Statistics 2016|publisher=|page=25}}</ref> Over 400 reactors generate electricity in 31 countries.<ref>{{cite web|url=http://www.uic.com.au/reactors.htm |title=World Power Reactors |accessdate=2016-05-06 |deadurl=unfit |archiveurl=https://web.archive.org/web/20080303234143/http://www.uic.com.au/reactors.htm |archivedate=March 3, 2008}}</ref>

A [[Yale University]] review published in the Journal of Industrial Ecology analyzing {{CO2}} [[life cycle assessment]](LCA) emissions from nuclear power([[light water reactor]]s) determined that: "The collective LCA literature indicates that life cycle [[Greenhouse gas|GHG]] emissions from nuclear power are only a fraction of traditional fossil sources and comparable to renewable technologies."<ref name="Warner + Heath, JoIE"/>
While some have raised uncertainty surrounding the future GHG emissions of nuclear power as a result of an extreme potential decline in uranium ore grade without a corresponding increase in the [[enriched uranium|efficiency of enrichment methods]]. In a scenario analysis of future global nuclear development, as it could be effected by a decreasing global [[uranium market]] of average ore grade, the analysis determined that depending on conditions, median life cycle nuclear power GHG emissions could be between 9 and 110&nbsp;g {{CO2}}-eq/kWh by 2050, with the latter high figure being derived from a "worst-case scenario" that is not "considered very robust" by the authors of the paper, as the "ore grade" in the scenario is lower than the uranium concentration in many lignite coal ashes.<ref name="Warner + Heath, JoIE">{{cite journal |last1= Warner |first1= E. S. |last2= Heath |first2= G. A. |doi= 10.1111/j.1530-9290.2012.00472.x |title= Life Cycle Greenhouse Gas Emissions of Nuclear Electricity Generation |journal= Journal of Industrial Ecology |volume= 16 |page= S73 |year= 2012 |pmid= |pmc=}}</ref>

Although this future analyses primarily deals with extrapolations for present [[Generation II reactor]] technology, the same paper also summarizes the literature on "FBRs"/[[Fast Breeder Reactor]]s, of which two are in operation as of 2014 with the newest being the [[BN-800 reactor|BN-800]], for these reactors it states that the "median life cycle GHG emissions&nbsp;... [are] similar to or lower than [present light water reactors] [[LWR]]s and purports to consume little or no uranium ore.''<ref name="Warner + Heath, JoIE"/>

In their 2014 report, the IPCC [[Comparisons of life-cycle greenhouse gas emissions|comparison of energy sources global warming potential per unit of electricity generated]], which notably included [[albedo]] effects, mirror the [[median]] emission value derived from the Warner and Heath Yale [[meta-analysis]] for the more common non-breeding [[light water reactor]]s, a [[carbon dioxide equivalent|CO2-equivalent]] value of 12&nbsp;g CO2-eq/kWh, which is the lowest global warming forcing of all [[baseload]] power sources, with comparable low carbon power baseload sources, such as hydropower and biomass, producing substantially more global warming forcing 24 and 230&nbsp;g CO2-eq/kWh respectively.<ref name="IPCC 2014 Annex III">{{cite web|title=IPCC Working Group III – Mitigation of Climate Change, Annex II I: Technology – specific cost and performance parameters|url=http://report.mitigation2014.org/drafts/final-draft-postplenary/ipcc_wg3_ar5_final-draft_postplenary_annex-iii.pdf|publisher=IPCC|accessdate=1 August 2014|page=10|year=2014|deadurl=yes|archiveurl=https://web.archive.org/web/20140616215117/http://report.mitigation2014.org/drafts/final-draft-postplenary/ipcc_wg3_ar5_final-draft_postplenary_annex-iii.pdf|archivedate=16 June 2014|df=}}</ref>

In 2014, [[Brookings Institution]] published ''The Net Benefits of Low and No-Carbon Electricity Technologies'' which states, after performing an energy and emissions cost analysis, that "The net benefits of new nuclear, hydro, and natural gas combined cycle plants far outweigh the net benefits of new wind or solar plants", with the most cost effective low carbon power technology being determined to be nuclear power.<ref>{{cite web|url=https://www.economist.com/news/finance-and-economics/21608646-wind-and-solar-power-are-even-more-expensive-commonly-thought-sun-wind-and|title=Free exchange: Sun, wind and drain|publisher=The Economist|quote=Sun, wind and drain Wind and solar power are even more expensive than is commonly thought|date=26 July 2014}}</ref><ref>[http://www.brookings.edu/~/media/research/files/papers/2014/05/19%20low%20carbon%20future%20wind%20solar%20power%20frank/net%20benefits%20final.pdf THE NET BENEFITS OF LOW AND NO-CARBON ELECTRICITY TECHNOLOGIES. MAY 2014, Charles Frank PDF] {{webarchive|url=https://web.archive.org/web/20150814175841/http://www.brookings.edu/~/media/research/files/papers/2014/05/19%20low%20carbon%20future%20wind%20solar%20power%20frank/net%20benefits%20final.pdf |date=2015-08-14}}</ref><ref>[http://economics.mit.edu/files/6317 Comparing the Costs of Intermittent and Dispatchable Electricity-Generating Technologies", by Paul Joskow, Massachusetts Institute of Technology, September 2011]</ref>

During his [[President of United States|presidential]] campaign, [[Barack Obama]] stated, "Nuclear power represents more than 70% of our noncarbon generated electricity. It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power as an option."<ref>{{cite web|url=http://www.barackobama.com/pdf/factsheet_energy_speech_080308.pdf |title=Archived copy |accessdate=November 21, 2012 |deadurl=yes |archiveurl=https://web.archive.org/web/20081017172925/http://www.barackobama.com/pdf/factsheet_energy_speech_080308.pdf |archivedate=October 17, 2008}}</ref>

[[File:Net US Electric Generation for 2009.jpg|thumb|This graph illustrates nuclear power is the United States's largest contributor of non-greenhouse-gas-emitting electric power generation, comprising nearly three-quarters of the non-emitting sources.]]

Analysis in 2015 by Professor and Chair of Environmental Sustainability [[Barry Brook (scientist)|Barry W. Brook]] and his colleagues on the topic of replacing fossil fuels entirely, from the electric grid of the world, has determined that at the historically modest and proven-rate at which nuclear energy was added to and replaced fossil fuels in France and Sweden during each nation's building programs in the 1980s, within 10 years nuclear energy could displace or remove fossil fuels from the electric grid completely, "allow[ing] the world to meet the most stringent greenhouse-gas mitigation targets.".<ref>{{cite journal|url=http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0124074|title=Potential for Worldwide Displacement of Fossil-Fuel Electricity by Nuclear Energy in Three Decades Based on Extrapolation of Regional Deployment Data|first1=Staffan A.|last1=Qvist|first2=Barry W.|last2=Brook|date=13 May 2015|publisher=|journal=PLoS ONE|volume=10|issue=5|page=e0124074|doi=10.1371/journal.pone.0124074|pmid=25970621|pmc=4429979|bibcode=2015PLoSO..1024074Q}}</ref> In a similar analysis, Brook had earlier determined that 50% of all [[world energy consumption|global energy]], that is not solely electricity, but transportation [[synfuels]] etc. could be generated within approximately 30 years, if the global nuclear fission build rate was identical to each of these nation's already proven decadal rates(in units of installed [[nameplate capacity]], [[gigawatt|GW]] per year, per unit of global [[GDP]](GW/year/$).<ref name="sciencedirect.com">{{cite journal|url=http://www.sciencedirect.com/science/article/pii/S0301421511009189|title=Could nuclear fission energy, etc., solve the greenhouse problem? The affirmative case|first=Barry W.|last=Brook|date=1 March 2012|publisher=|journal=Energy Policy|volume=42|pages=4–8|doi=10.1016/j.enpol.2011.11.041}}</ref><ref name="onlinelibrary.wiley.com">{{cite journal|url=http://onlinelibrary.wiley.com/doi/10.1002/wcc.324/abstract|title=A critical review of global decarbonization scenarios: what do they tell us about feasibility?|first1=Peter J.|last1=Loftus|first2=Armond M.|last2=Cohen|first3=Jane C. S.|last3=Long|first4=Jesse D.|last4=Jenkins|date=1 January 2015|publisher=|journal=WIREs Clim Change|volume=6|issue=1|pages=93–112|doi=10.1002/wcc.324}}</ref><ref name="qualenergia.it">[http://www.qualenergia.it/sites/default/files/articolo-doc/wcc324-1.pdf A critical review of global decarbonization scenarios: what do they tell us about feasibility? Open access PDF]</ref>

This is in contrast to the completely conceptual paper-studies for a ''[[100% renewable energy]]'' world, which would require an [[orders of magnitude]] more costly global investment per year, an investment rate that has no historical precedent, having never been attempted due to its prohibitive cost,<ref name="onlinelibrary.wiley.com"/><ref>[http://www.qualenergia.it/sites/default/files/articolo-doc/wcc324-1.pdf A critical review of global decarbonization scenarios: what do they tell us about feasibility? Open access PDF. Figure 6]</ref> and with far greater land area that would be required to be devoted to the wind, wave and solar projects, along with the inherent assumption that humanity will use less, and not more, energy in the future.<ref name="sciencedirect.com"/><ref name="onlinelibrary.wiley.com"/><ref name="qualenergia.it"/> As Brook notes the "principal limitations on nuclear fission are not technical, economic or fuel-related, but are instead linked to complex issues of societal acceptance, fiscal and political inertia, and inadequate critical evaluation of the real-world constraints facing [the other] low-carbon alternatives."<ref name="sciencedirect.com"/>

Nuclear power may be uncompetitive compared with fossil fuel energy sources in countries without a [[carbon tax]] program, and in comparison to a fossil fuel plant of the same power output, nuclear power plants take a longer amount of time to construct.<ref>Trevor Findlay. [http://www.cigionline.org/library/future-nuclear-energy-2030-and-its-implications-safety-security-and-nonproliferation-overvie The Future of Nuclear Energy to 2030 and its Implications for Safety, Security and Nonproliferation] {{webarchive|url=https://web.archive.org/web/20110616190800/http://www.cigionline.org/library/future-nuclear-energy-2030-and-its-implications-safety-security-and-nonproliferation-overvie |date=2011-06-16}} February 4, 2010.</ref><ref name=tf2010>Trevor Findlay (2010). [http://www.cigionline.org/sites/default/files/Nuclear%20Energy%20Futures%20Overview.pdf The Future of Nuclear Energy to 2030 and its Implications for Safety, Security and Nonproliferation: Overview] {{webarchive|url=https://web.archive.org/web/20130512210155/http://www.cigionline.org/sites/default/files/Nuclear%20Energy%20Futures%20Overview.pdf |date=2013-05-12}}, The Centre for International Governance Innovation (CIGI), Waterloo, Ontario, Canada, pp. 10–11.</ref><ref>[[M.V. Ramana]]. Nuclear Power: Economic, Safety, Health, and Environmental Issues of Near-Term Technologies, ''Annual Review of Environment and Resources'', 2009, 34, pp. 144–45.</ref><ref name=iea2009>International Energy Agency, ''World Energy Outlook'', 2009, p. 160.</ref>

Two new, first of their kind, [[European Pressurized Reactor|EPR]] reactors under construction in Finland and France have been delayed and are running over-budget.<ref name=jk>James Kanter. [https://www.nytimes.com/2009/05/29/business/energy-environment/29nuke.html?ref=global-home In Finland, Nuclear Renaissance Runs Into Trouble] ''New York Times'', May 28, 2009.</ref><ref name=greeninc>James Kanter. [http://greeninc.blogs.nytimes.com/2009/05/29/is-the-nuclear-renaissance-fizzling/ Is the Nuclear Renaissance Fizzling?] ''Green'', 29 May 2009.</ref><ref name=rb>Rob Broomby. [http://news.bbc.co.uk/2/hi/europe/8138869.stm Nuclear dawn delayed in Finland] ''BBC News'', 8 July 2009.</ref> However learning from experience, two further EPR reactors under construction in China are on, and ahead, of schedule respectively.<ref>{{cite news |url=https://www.bloomberg.com/news/2010-11-24/china-builds-french-designed-nuclear-reactor-for-40-less-areva-ceo-says.html |work=Bloomberg |title=China Builds Nuclear Reactor for 40% Less Than Cost in France, Areva Says}}</ref> As of 2013, according to the [[IAEA]] and the [[European Nuclear Society]], worldwide there were 68 civil nuclear power reactors under construction in 15 countries.<ref>{{cite web|url=http://www.iaea.org/pris/ |title=PRIS – Home |publisher=Iaea.org |date= |accessdate=2016-05-06}}</ref><ref name="euronuclear.org">{{cite web|author=Author: Marion Brünglinghaus, ENS, European Nuclear Society |url=http://www.euronuclear.org/info/encyclopedia/n/nuclear-power-plant-world-wide.htm |title=Nuclear power plants, world-wide |publisher=Euronuclear.org |date= |accessdate=2016-05-06}}</ref> China has 29 of these nuclear power reactors under construction, as of 2013, with plans to build many more,<ref name="euronuclear.org"/><ref name="Nuclear Power in China">World Nuclear Association (December 10, 2010). [http://www.world-nuclear.org/info/inf63.html Nuclear Power in China]</ref> while in the US the licenses of almost half its reactors have been extended to 60&nbsp;years,<ref name="Nuclear Power in the USA">{{cite web |url= http://www.world-nuclear.org/info/inf41.html#licence |title= Nuclear Power in the USA |date=June 2008 |work= |publisher= [[World Nuclear Association]] |accessdate= 2008-07-25}}</ref> and plans to build another dozen are under serious consideration.<ref name=matt2010>Matthew L. Wald (December 7, 2010). [http://green.blogs.nytimes.com/2010/12/07/nuclear-renaissance-is-short-on-largess/ Nuclear 'Renaissance' Is Short on Largess] ''[[The New York Times]]''.</ref> There are also a considerable number of new reactors being built in South Korea, India, and Russia. At least 100 older and smaller reactors will "most probably be closed over the next 10–15 years".<ref name=ditt>Michael Dittmar. [http://www.smh.com.au/business/taking-stock-of-nuclear-renaissance-that-never-was-20100817-128ky.html Taking stock of nuclear renaissance that never was] ''Sydney Morning Herald'', August 18, 2010.</ref> This is probable only if one does not factor in the ongoing [[Light Water Reactor Sustainability Program]], created to permit the extension of the life span of the USA's 104 nuclear reactors to 60 years. The licenses of almost half of the USA's reactors have been extended to 60&nbsp;years as of 2008.<ref name="Nuclear Power in the USA"/> Two new "[[passive safety]]" [[AP1000]] reactors are, as of 2013, being constructed at [[Vogtle Electric Generating Plant]].

Public opinion about nuclear power varies widely between countries.<ref>{{harvnb|Gallup International|2011|pp=9–10}}</ref><ref>{{harvnb|Ipsos|2011|p=4}}</ref> A poll by Gallup International (2011)<ref>{{harvnb|Gallup International|2011}}</ref> assessed public opinion in 47 countries. The poll was conducted following a [[2011 Tōhoku earthquake and tsunami|tsunami and earthquake]] which caused an [[Fukushima Daiichi nuclear disaster|accident]] at the Fukushima nuclear power plant in Japan. 49% stated that they held favourable views about nuclear energy, while 43% held an unfavourable view.<ref>{{harvnb|Gallup International|2011|p=3}}</ref> Another global survey by Ipsos (2011)<ref>{{harvnb|Ipsos|2011}}</ref> assessed public opinion in 24 countries. Respondents to this survey showed a clear preference for renewable energy sources over coal and nuclear energy (refer to graph opposite).<ref name="ipsos 2011 preference for renewables">{{harvnb|Ipsos|2011|p=3}}</ref> Ipsos (2012)<ref>{{citation
|author=Ipsos
|title=After Fukushima: Global Opinion on Energy Policy
|date=9 March 2012
|url=http://www.ipsos.com/public-affairs/sites/www.ipsos.com.public-affairs/files/Energy%20Article.pdf
}}, p. 7. Survey website: [http://www.ipsos.com/public-affairs/publications/after-fukushima-global-opinion-energy-policy After Fukushima: Global Opinion on Energy Policy: Ipsos Public Affairs]</ref> found that solar and wind were viewed by the public as being more environmentally friendly and more viable long-term energy sources relative to nuclear power and natural gas. However, solar and wind were viewed as being less reliable relative to nuclear power and natural gas. In 2012 a poll done in the UK found that 63% of those surveyed support nuclear power, and with opposition to nuclear power at 11%.<ref>{{cite web|url=https://www.reuters.com/article/britain-nuclear-poll-idAFL6E8I2E4H20120702|title=UK popular support for nuclear power rises -poll|date=2 July 2016|publisher=Reuters}}</ref> In Germany, strong [[anti-nuclear]] sentiment led to eight of the seventeen operating reactors being permanently shut down following the March 2011 [[Fukushima nuclear disaster]].<ref name="Annika Breidthardt">{{cite news |url=http://uk.reuters.com/article/2011/05/30/us-germany-nuclear-idUKTRE74Q2P120110530 |title=German government wants nuclear exit by 2022 at latest |author=Annika Breidthardt |date=May 30, 2011 |work=Reuters}}</ref>

[[Nuclear fusion]] research, in the form of the [[International Thermonuclear Experimental Reactor]] is underway. Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been. However, the extreme requirements for continuous reactions and [[plasma containment]] led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production was still believed to be unlikely before 2050.<ref name="ITERorg">{{cite web |work=The ITER Project |title=Beyond ITER |publisher=Information Services, Princeton Plasma Physics Laboratory |url=http://www.iter.org/Future-beyond.htm |accessdate=5 February 2011 |archiveurl=https://web.archive.org/web/20061107220145/http://www.iter.org/Future-beyond.htm |archivedate=7 November 2006}} – Projected fusion power timeline</ref> Although rather than an either, or, issue economical [[fusion-fission hybrid reactor]]s could be built before any attempt at this more demanding commercial "[[fusion power|pure-fusion reactor]]"/[[DEMOnstration Power Station|DEMO]] reactor takes place.<ref>{{cite journal|url=http://www.ans.org/pubs/journals/nt/a_36037|title=The SABrR Concept for A Fission-Fusion Hybrid <sup>238</sup>U-to-<sup>239</sup>Pu Fissile Production Reactor|first1=C. L.|last1=Stewart|first2=W. M.|last2=Stacey|date=1 July 2014|publisher=|journal=NT|volume=187|issue=1|page=1|doi=10.13182/NT13-102}}</ref>

====Coal to gas fuel switching====
{{See also|Emission intensity}}
Most mitigation proposals imply—rather than directly state—an eventual reduction in global fossil fuel production. Also proposed are direct quotas on global fossil fuel production.<ref>{{cite web
|title= Climate Control: a proposal for controlling global greenhouse gas emissions
|publisher= Sustento Institute
|url= http://sustento.org.nz/wp-content/uploads/2007/06/climate-control.pdf
|archive-url= https://web.archive.org/web/20080216014928/http://sustento.org.nz/wp-content/uploads/2007/06/climate-control.pdf
|dead-url= yes
|archive-date= 2008-02-16
|format= PDF
|accessdate= 2007-12-10
}}</ref><ref>{{cite web
|title=#7: Moratorium on New Projects for Fossil Fuel Production & Declining Cap on Existing Production
|url=http://www.bcsea.org/policy/files/7_Fossil_fuels.pdf
|first=Thomas|last=Hackney
|publisher=[[BC Sustainable Energy Association]]
|date=July 2009
|series=[http://www.bcsea.org/policy/ BCSEA's Climate Action Portfolio]
|accessdate=2008-04-24}}</ref>

Natural gas emits far fewer greenhouse gases (i.e. {{CO2}} and methane—CH<sub>4</sub>) than coal when burned at power plants, but evidence has been emerging that this benefit could be completely negated by methane leakage at gas drilling fields and other points in the supply chain.

A study performed by the Environmental Protection Agency (EPA) and the Gas Research Institute (GRI) in 1997 sought to discover whether the reduction in carbon dioxide emissions from increased natural gas (predominantly methane) use would be offset by a possible increased level of [[methane emissions]] from sources such as leaks and emissions. The study concluded that the reduction in emissions from increased natural gas use outweighs the detrimental effects of increased methane emissions. More recent peer-reviewed studies have challenged the findings of this study, with researchers from the National Oceanic and Atmospheric Administration (NOAA) reconfirming findings of high rates of methane (CH4) leakage from natural gas fields.

A 2011 study<ref name="usclimatenetwork.org">http://www.usclimatenetwork.org/resource-database/report-coal-to-gas-the-influence-of-methane-leakage</ref> by noted climate research scientist, Tom Wigley,<ref>[[Tom Wigley]]</ref> found that while carbon dioxide ({{CO2}}) emissions from fossil fuel combustion may be reduced by using natural gas rather than coal to produce energy, it also found that additional methane (CH4) from leakage adds to the radiative forcing of the climate system, offsetting the reduction in {{CO2}} forcing that accompanies the transition from coal to gas. The study looked at methane leakage from coal mining; changes in radiative forcing due to changes in the emissions of sulfur dioxide and carbonaceous aerosols; and differences in the efficiency of electricity production between coal- and gas-fired power generation. On balance, these factors more than offset the reduction in warming due to reduced {{CO2}} emissions. When gas replaces coal there is additional warming out to 2,050 with an assumed leakage rate of 0%, and out to 2,140 if the leakage rate is as high as 10%. The overall effects on global-mean temperature over the 21st century, however, are small. Petron et al. (2013)<ref name="epa.gov">http://www.epa.gov/ttnchie1/conference/ei20/session6/gpetron.pdf</ref> and Alvarez et al. (2012)<ref>{{cite journal|url=http://www.pnas.org/content/early/2012/04/02/1202407109.abstract |title=Greater focus needed on methane leakage from natural gas infrastructure |date= |accessdate=2016-05-06 |doi=10.1073/pnas.1202407109 |volume=109 |issue=17 |journal=Proceedings of the National Academy of Sciences |pages=6435–40|bibcode=2012PNAS..109.6435A |year=2012 |last1=Alvarez |first1=R. A |last2=Pacala |first2=S. W |last3=Winebrake |first3=J. J |last4=Chameides |first4=W. L |last5=Hamburg |first5=S. P}}</ref> note that estimated that leakage from gas infrastructure is likely to be underestimated. These studies indicate that the exploitation of natural gas as a "cleaner" fuel is questionable. A 2014 meta-study of 20 years of natural gas technical literature shows that methane emissions are consistently underestimated but on a 100-year scale, the climate benefits of coal to gas fuel switching are likely larger than the negative effects of natural gas leakage.<ref>{{cite journal |volume= 343 |issue= 6172 |pages= 733–35 |last1= Brandt |first1= A. R. |last2= Heath |first2= G. A. |last3= Kort |first3= E. A. |last4= O'Sullivan |first4= F. |last5= Pétron |first5= G. |last6= Jordaan |first6= S. M. |last7= Tans |first7= P. |last8= Wilcox |first8= J. |last9= Gopstein |first9= A. M. |last10= Arent |first10= D. |last11= others |title= Methane leaks from North American natural gas systems |journal= Science |accessdate= 2015-04-29 |date= 2014 |url= http://psb.vermont.gov/sites/psb/files/CLF-SC-2%20Science-Methane%20Leaks.pdf|bibcode= 2014Sci...343..733B |doi= 10.1126/science.1247045 |pmid=24531957}}</ref>

====Heat pump====
{{Main|Heat pump}}
[[File:Outunit of heat pump.jpg|thumb|Outside unit of an air-source heat pump]]
A heat pump is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move [[thermal energy]] opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

While [[air conditioner]]s and [[freezer]]s are familiar examples of heat pumps, the term "heat pump" is more general and applies to many [[HVAC]] (heating, ventilating, and air conditioning) devices used for space heating or space cooling. When a heat pump is used for heating, it employs the same basic [[heat pump and refrigeration cycle|refrigeration-type cycle]] used by an air conditioner or a refrigerator, but in the opposite direction—releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground.<ref>[http://www.nrel.gov/docs/fy01osti/28037.pdf Air-source heat pumps] [[National Renewable Energy Laboratory]] June 2011</ref> In heating mode, heat pumps are three to four times [[efficient energy use|more efficient]] in their use of electric power than simple electrical resistance heaters.

It has been concluded that heat pumps are the single technology that could reduce the greenhouse gas emissions of households better than every other technology that is available on the market. With a market share of 30% and (potentially) clean electricity, heat pumps could reduce global CO2 emissions by 8% annually.<ref>{{cite journal |author= Staffell Iain ''et al.'' |year= 2012 |title= A review of domestic heat pumps |url= |journal= [[Energy and Environmental Science]] |volume= 5 |issue= 11 |pages= 9291–9306 |doi= 10.1039/c2ee22653g}}</ref> Using ground source heat pumps could reduce around 60% of the [[primary energy]] demand and 90% of CO2 emissions in Europe in 2050 and make handling high shares of renewable energy easier.<ref>{{cite journal |last1= Carvalho |first1= |display-authors= 1 |last2= et al |year= 2015 |title= Ground source heat pump carbon emissions and primary energy reduction potential for heating in buildings in Europe—results of a case study in Portugal |url= |journal= [[Renewable and Sustainable Energy Reviews]] |volume= 45 |issue= |pages= 755–768 |doi= 10.1016/j.rser.2015.02.034}}</ref> Using surplus renewable energy in heat pumps is regarded as the most effective household means to reduce global warming and fossil fuel depletion.<ref>{{cite journal |author= Sternberg André, Bardow André |year= 2015 |title= ''Power-to-What? – Environmental assessment of energy storage systems''. In |url= |journal= [[Energy and Environmental Science]] |volume= 8 |issue= 2 |pages= 389–400 |doi= 10.1039/c4ee03051f}}</ref>

With significant amounts of fossil fuel used in electricity production, demands on the electrical grid also generate greenhouse gases. Without a high share of low-carbon electricity, a domestic heat pump will produce more carbon emissions than using natural gas.<ref>[http://www.energysolutionscenter.org/assets/1/Page/GHP_Position_Paper_and_apndx_031710.pdf pg 7]</ref>

====Fossil fuel phase-out: carbon neutral and negative fuels====
[[File:Baggerbesetzung Welzow Süd.jpg|thumb|3,500–4,000 [[environmental activist]]s blocking a coal mine in Germany to limit climate change ([[Ende Gelände 2016]])]]
{{Main|Fossil fuel phase-out}}

Fossil fuel may be phased-out with [[carbon-neutral fuel|carbon-neutral and carbon-negative]] pipeline and transportation fuels created with [[power to gas]] and [[gas to liquids]] technologies.<ref>{{cite web|last1=Dodge|first1=Edward|title=Power-to-Gas Enables Massive Energy Storage|url=http://theenergycollective.com/ed-dodge/2166976/power-gas-enables-massive-energy-storage|website=TheEnergyCollective.com|accessdate=25 May 2015|date=December 6, 2014}}</ref><ref>{{cite book|last1=Ground|first1=Lukas|last2=Schulze|first2=Paula|last3=Holstein|first3=Johan|title=Systems Analysis Power to Gas|date=June 20, 2013|publisher=DNV, KEMA Nederland B.V.|location=Groningen|url=http://www.dnv.com/binaries/DNV%20KEMA%20%282013%29%20-%20Systems%20Analyses%20Power%20to%20Gas%20-%20Technology%20Review_tcm4-567461.pdf|accessdate=25 May 2015}}{{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes}}</ref><ref>[https://m.youtube.com/watch?t=0m55s&v=JBv8xUWMY7E "Shell Pearl GTL – Andy Brown"] Royal Dutch Shell Company video, March 18, 2011.</ref><ref>{{cite news|last1=Scott|first1=Mark|title=Energy for a Rainy Day, or a Windless One|url=https://www.nytimes.com/2014/10/08/business/energy-for-a-rainy-day-or-a-windless-one.html|accessdate=26 May 2015|work=New York Times|date=October 7, 2014}}</ref><ref>{{cite news|last1=Randall|first1=Tom|title=Seven Reasons Cheap Oil Can't Stop Renewables Now|url=https://www.bloomberg.com/news/articles/2015-01-30/seven-reasons-cheap-oil-can-t-stop-renewables-now|accessdate=26 May 2015|work=BloombergBusiness|agency=Bloomberg L.P.|date=January 30, 2015}}</ref> [[Carbon dioxide]] from fossil fuel [[flue gas]] can be used to produce [[lumber#Plastic lumber|plastic lumber]] allowing carbon negative [[reforestation]].<ref>{{cite web|url=http://co2-chemistry.eu/ |title=Home – 5th Conference on Carbon Dioxide as Feedstock for Fuels, Chemistry and Polymers |publisher=Co2-chemistry.eu |date=2008-12-01 |accessdate=2016-05-06}}</ref>

{{Expand section|date=May 2015}}

===Sinks and negative emissions===
{{Main|Carbon sink|Negative carbon dioxide emission}}

A [[carbon sink]] is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period, such as a growing [[forest]]. A [[negative carbon dioxide emission]] on the other hand is a permanent removal of carbon dioxide out of the atmosphere. Examples are [[carbon capture and storage|direct air capture]], [[enhanced weathering]] technologies such as storing it in [[geologic sequestration of CO2|geologic formations]] underground and [[biochar]]. These processes are sometimes considered as variations of sinks or mitigation,<ref>{{cite web
|title=OECD Environmental Outlook to 2050, Climate Change Chapter, pre-release version
|url=http://www.oecd.org/dataoecd/32/53/49082173.pdf
|publisher=[[OECD]]
|year=2011
|accessdate=2012-04-23
}}</ref><ref name="IEA Technology Roadmap Carbon Capture and Storage 2009">{{cite web
|title=IEA Technology Roadmap Carbon Capture and Storage 2009
|url=https://www.iea.org/papers/2009/CCS_Roadmap.pdf
|publisher=[[OECD]]/IEA
|year=2009
|accessdate=2012-04-23
}}</ref> and sometimes as geoengineering.<ref>{{cite web
|title=Geoengineering the climate: science, governance and uncertainty
|url=http://royalsociety.org/policy/publications/2009/geoengineering-climate/
|publisher=[[The Royal Society]]
|year=2009
|accessdate=2012-04-23
}}</ref> In combination with other mitigation measures, sinks in combination with negative carbon emissions are considered crucial for meeting the [[climate change mitigation scenarios#350 ppm|350 ppm target]].<ref name=hare>{{cite journal |last1= Hare |first1= B. |last2= Meinshausen |first2= M. |doi= 10.1007/s10584-005-9027-9 |title= How Much Warming are We Committed to and How Much can be Avoided? |journal= Climatic Change |volume= 75 |pages= 111–49 |year= 2006 |pmid= |pmc=}}</ref><ref name=Azar>Azar, C., Lindgren, K., Larson, E.D. and Möllersten, K.: (2006)[http://www.environmental-expert.com/Files%5C6063%5Carticles%5C6220%5Cw30h4274h130580u.pdf "Carbon capture and storage from fossil fuels and biomass – Costs and potential role in stabilising the atmosphere"], Climatic Change, 74, 47–79.</ref><ref>{{cite web
|title=OECD Environmental Outlook to 2050, Climate Change Chapter, pre-release version
|url=http://www.oecd.org/dataoecd/32/53/49082173.pdf
|publisher=[[OECD]]
|year=2011
|accessdate=2012-01-16
}}</ref>

The Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC) notes that one third of humankind's annual emissions of {{CO2}} are absorbed by the oceans.<ref>{{cite web|url=http://www.acecrc.org.au/Research/Southern%20Ocean%20Carbon%20Sink |title=Archived copy |accessdate=July 21, 2013 |deadurl=yes |archiveurl=https://web.archive.org/web/20130811112807/http://www.acecrc.org.au/Research/Southern%20Ocean%20Carbon%20Sink |archivedate=August 11, 2013}}</ref> However, this also leads to [[ocean acidification]], with potentially significant impacts on marine life.<ref>{{cite web|url=http://www.csiro.au/Outcomes/Climate/Understanding/ClimateChangeCO2inOceans.aspx |title=Archived copy |accessdate=July 21, 2013 |deadurl=yes |archiveurl=https://web.archive.org/web/20130514141655/http://www.csiro.au/Outcomes/Climate/Understanding/ClimateChangeCO2inOceans.aspx |archivedate=May 14, 2013}}</ref> Acidification lowers the level of carbonate ions available for calcifying organisms to form their shells. These organisms include plankton species that contribute to the foundation of the Southern Ocean food web. However acidification may impact on a broad range of other physiological and ecological processes, such as fish respiration, larval development and changes in the solubility of both nutrients and toxins.<ref>{{cite web|url=http://www.acecrc.org.au/Research/Ocean%20Acidification |title=Archived copy |accessdate=July 21, 2013 |deadurl=yes |archiveurl=https://web.archive.org/web/20130811132348/http://www.acecrc.org.au/Research/Ocean%20Acidification |archivedate=August 11, 2013}}</ref>

====Reforestation and afforestation====
[[File:Shennongjia virgin forest.jpg|thumb|Transferring [[land rights]] to indigenous inhabitants is argued to efficiently conserve forests. Regrowth of [[secondary forest|forests]] on abandoned farmland restores more forest than that lost to [[deforestation]].]]
{{Main|Deforestation|Reforestation|Biosequestration}}

Almost 20 percent (8{{nbsp}}GtCO<sub>2</sub>/year) of total greenhouse-gas emissions were from deforestation in 2007. It is estimated that avoided deforestation reduces CO<sub>2</sub> emissions at a rate of 1{{nbsp}}tonne of CO<sub>2</sub> per $1–5 in [[opportunity costs]] from lost agriculture. [[Reforestation]] could save at least another 1{{nbsp}}GtCO<sub>2</sub>/year, at an estimated cost of $5–15/tCO<sub>2</sub>.<ref name="stern"/> [[Afforestation]] is where there was previously no forest - such plantations are estimated to have to be prohibitively massive to be reduce emissions by itself.<ref>Lena R. Boysen, Wolfgang Lucht, Dieter Gerten, Vera Heck, Timothy M. Lenton, Hans Joachim Schellnhuber. The limits to global-warming mitigation by terrestrial carbon removal. ''Earth's Future'', 2017; https://www.sciencedaily.com/releases/2017/05/170518104038.htm DOI: 10.1002/2016EF000469</ref>

Transferring rights over land from public domain to its indigenous inhabitants is argued to be a cost effective strategy to conserve forests.<ref name=Guardian1>{{cite news|url= https://www.theguardian.com/global-development/2016/jul/22/india-follow-china-saving-forest-people-land-rights|title=India should follow China to find a way out of the woods on saving forest people|publisher=The Guardian |access-date=2 November 2016|date=22 July 2016}}</ref> This includes the protection of such rights entitled in existing laws, such as India's [[The Scheduled Tribes and Other Traditional Forest Dwellers (Recognition of Forest Rights) Act, 2006|Forest Rights Act]].<ref name=Guardian1/> The transferring of such rights in [[China]], perhaps the largest [[land reform]] in modern times, has been argued to have increased forest cover.<ref name=rightsandresources>{{cite web|url=http://rightsandresources.org/en/publication/view/chinas-forest-tenure-reforms-impacts-and-implications-for-choice-conservation-and-climate-change/|title=China's forest tenure reforms|publisher=rightsandresources.org |accessdate=7 August 2016}}</ref> In [[Brazil]], forested areas given tenure to indigenous groups have even lower rates of clearing than [[national park]]s.<ref name=rightsandresources/> A 2016 report concludes that modest investments in indigenous land rights will generate economic, social, and environmental returns for the communities involved and for climate protection. The report quantifies the economic value of securing such rights, with a focus on the Amazon region.<ref name="ding-etal-2016-webpage">{{cite web
|first1= Helen | last1= Ding
|first2= Peter | last2= Veit
|first3= Erin | last3= Gray
|first4= Katie | last4= Reytar
|first5= Juan-Carlos | last5= Altamirano
|first6= Allen | last6= Blackman
|first7= Benjamin | last7= Hodgdon
|date= October 2016
|title= Climate benefits, tenure costs: The economic case for securing indigenous land rights in the Amazon
|website= World Resources Institute (WRI)
|location= Washington DC, USA
|url= http://www.wri.org/publication/climate-benefits-tenure-costs
|access-date= 2016-11-02
}}</ref><ref name="ding-etal-2016">{{cite book
|first1= Helen | last1= Ding
|first2= Peter G | last2= Veit
|first3= Allen | last3= Blackman
|first4= Erin | last4= Gray
|first5= Katie | last5= Reytar
|first6= Juan-Carlos | last6= Altamirano
|first7= Benjamin | last7= Hodgdon
|date= 2016
|title= Climate benefits, tenure costs: The economic case for securing indigenous land rights in the Amazon
|publisher= World Resources Institute (WRI)
|location= Washington DC, USA
|isbn= 978-1-56973-894-8
|url= http://www.wri.org/sites/default/files/Climate_Benefits_Tenure_Costs.pdf
|access-date= 2016-11-02
}}</ref>

With increased [[intensive agriculture]] and [[urbanization]], there is an increase in the amount of abandoned farmland. By some estimates, for every half a hectare of original [[old-growth forest]] cut down, more than 20 hectares of new [[secondary forest]]s are growing, even though they do not have the same biodiversity as the original forests and original forests store 60% more carbon than these new secondary forests.<ref>{{cite news|url= https://www.nytimes.com/2009/01/30/science/earth/30forest.html?pagewanted=all|title=New Jungles Prompt a Debate on Rain Forests|publisher=New York Times |accessdate=18 July 2016|date=29 January 2009}}</ref><ref>Young, E. (2008). ''IPCC Wrong On Logging Threat to Climate.'' New Scientist, August 5, 2008. Retrieved on August 18, 2008, from https://www.newscientist.com/article/dn14466-ipcc-wrong-on-logging-threat-toclimate.html</ref> According to a study in ''[[Science (journal)|Science]]'', promoting regrowth on abandoned farmland could offset years of carbon emissions.<ref>{{cite news|url= https://www.nytimes.com/2016/05/17/science/forests-carbon-dioxide.html?_r=1|title=In Latin America, Forests May Rise to Challenge of Carbon Dioxide|publisher=New York Times |accessdate=18 July 2016|date=16 May 2016}}</ref>

====Avoided desertification====
[[File:Cow female black white.jpg|thumb|Managed grazing methods are argued to be able to restore grasslands, thereby significantly decreasing atmospheric CO<sub>2</sub> levels.<ref name=ASavory/>]]

Restoring grasslands store CO<sub>2</sub> from the air into plant material. Grazing livestock, usually not left to wander, would eat the grass and would minimize any grass growth. However, grass left alone would eventually grow to cover its own growing buds, preventing them from photosynthesizing and the dying plant would stay in place.<ref name=Tlovell>{{cite news|url=http://www.newstatesman.com/environment/2011/01/lovell-carbon-ward-climate|title=How fences could save the planet|publisher=newstatesman.com|accessdate=May 5, 2013|date=January 13, 2011}}</ref> A method proposed to restore grasslands uses fences with many small paddocks and moving herds from one paddock to another after a day a two in order to mimick natural grazers and allowing the grass to grow optimally.<ref name=Tlovell/><ref>{{cite news|url=http://news.mongabay.com/2008/0221-soil_carbon_lovell_interview.html|title=Restoring soil carbon can reverse global warming, desertification and biodiversity|publisher=mongabay.com|accessdate=May 5, 2013|date=February 21, 2008|deadurl=yes|archiveurl=https://archive.is/20130625040133/http://news.mongabay.com/2008/0221-soil_carbon_lovell_interview.html|archivedate=June 25, 2013|df=}}</ref><ref>{{cite news|url=http://www.time.com/time/magazine/article/0,9171,1953692,00.html|title=How eating grass-fed beef could help fight climate change|publisher=time.com|accessdate=May 11, 2013|date=January 25, 2010}}</ref> Additionally, when part of leaf matter is consumed by a herding animal, a corresponding amount of root matter is sloughed off too as it would not be able to sustain the previous amount of root matter and while most of the lost root matter would rot and enter the atmosphere, part of the carbon is sequestered into the soil.<ref name=Tlovell/> It is estimated that increasing the carbon content of the soils in the world's 3.5 billion hectares of agricultural grassland by 1% would offset nearly 12 years of CO<sub>2</sub> emissions.<ref name=Tlovell/> [[Allan Savory]], as part of [[holistic management]], claims that while large herds are often blamed for [[desertification]], prehistoric lands supported large or larger herds and areas where herds were removed in the United States are still desertifying.<ref name=ASavory>{{cite news|url=http://newswatch.nationalgeographic.com/2013/03/06/how-cows-could-repair-the-world-allan-savory-at-ted/|title=How cows could repair the world|publisher=nationalgeographic.com|accessdate=May 5, 2013|date=March 6, 2013}}</ref>

====Carbon capture and storage====
[[File:Carbon sequestration-2009-10-07.svg|thumb|350px|Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a coal-fired plant]]
{{Main|Carbon capture and storage}}

Carbon capture and storage (CCS) is a method to mitigate climate change by capturing [[carbon dioxide]] (CO<sub>2</sub>) from large point sources such as power plants and subsequently storing it away safely instead of releasing it into the atmosphere. The IPCC estimates that the costs of halting global warming would double without CCS.<ref name=guardian0916>{{cite news|url=https://www.theguardian.com/environment/2016/jun/09/co2-turned-into-stone-in-iceland-in-climate-change-breakthrough|title=CO2 turned into stone in Iceland in climate change breakthrough|publisher=The Guardian|accessdate=2 September 2017|date=9 June 2016}}</ref> The International Energy Agency says CCS is "the most important single new technology for CO<sub>2</sub> savings" in power generation and industry.<ref name=futureenergysummit>{{cite news|last=Robinson |first=Simon |url=http://www.time.com/time/specials/packages/article/0,28804,1954176_1954175,00.html |title=How to Reduce Carbon Emissions: Capture and Store it? |publisher=[[Time.com]] |date=2010-01-22 |accessdate=2010-08-26}}</ref> Though it requires up to 40% more energy to run a CCS coal power plant than a regular coal plant, CCS could potentially capture about 90% of all the carbon emitted by the plant.<ref name=futureenergysummit/> Norway's [[Sleipner gas field]], beginning in 1996, stores almost a million tons of CO<sub>2</sub> a year to avoid penalties in producing natural gas with unusually high levels of CO<sub>2</sub>.<ref>https://sequestration.mit.edu/tools/projects/sleipner.html</ref><ref name=futureenergysummit/> As of late 2011, the total planned {{CO2}} storage capacity of all 14 projects in operation or under construction is over 33 million tonnes a year. This is broadly equivalent to preventing the emissions from more than six million cars from entering the atmosphere each year.<ref>{{cite web|url=http://www.globalccsinstitute.com/publications/global-status-ccs-2011/online/26856|title=Global Status of CCS Report:2011|publisher=Global CCS Institute|accessdate=2011-12-14}}</ref> According to a [[Sierra Club]] analysis, the US coal fired [[Kemper Project]] due to be online in 2017, is the most expensive power plant ever built for the watts of electricity it will generate.<ref name="Drajem">{{cite web |last= Drajem |first= Mark |title= Coal's Best Hope Rising With Costliest U.S. Power Plant |publisher= Bloomberg Business |date= April 14, 2014 |url= https://www.bloomberg.com/news/articles/2014-04-14/coal-s-best-hope-rising-with-costliest-u-s-power-plant}}</ref>

====Enhanced weathering====
Enhanced weathering is the removal of carbon from the air into the earth, enhancing the natural carbon cycle where carbon is mineralized into rock. The [[CarbFix]] project couples with carbon capture and storage in power plants to turn carbon dioxide into stone in a relatively short period of two years, addressing the common concern of leakage in CCS projects. While this project used [[basalt]] rocks, [[olivine]] has also shown promise.<ref name=guardian0916/>

===Geoengineering===
{{Main|Climate engineering}}

Geoengineering is seen by Olivier Sterck as an alternative to mitigation and adaptation, but by Gernot Wagner as an entirely separate response to climate change.<ref>https://halshs.archives-ouvertes.fr/halshs-00635487/</ref><ref>http://www.climatecentral.org/news/harvard-scientists-taking-geoengineering-into-the-field-21362</ref> In a [[scientific literature|literature]] assessment, Barker ''et al.'' (2007) described geoengineering as a type of mitigation policy.<ref>{{cite book
|year=2007
|title=11.2.2 Ocean fertilization and other geo-engineering options. In (book chapter): Mitigation from a cross-sectoral perspective. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (B. Metz ''et al.'' (eds.))
|publisher=Print version: Cambridge University Press, Cambridge, UK, and New York, NY, US. This version: IPCC website
|isbn=978-0-521-88011-4
|author=Barker, T.
|url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch11s11-2-2.html
|accessdate=2010-04-05|display-authors=etal}}</ref> IPCC (2007) concluded that geoengineering options, such as ocean fertilization to remove CO<sub>2</sub> from the [[atmosphere]], remained largely unproven.<ref>{{cite book
|year=2007
|title=C. Mitigation in the short and medium term (until 2030). In (book section): Summary for Policymakers. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (B. Metz ''et al.'' (eds.))
|publisher=Print version: Cambridge University Press, Cambridge, UK, and New York, NY, US. This version: IPCC website
|isbn=978-0-521-88011-4
|author=IPCC
|url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/spmsspm-c.html
|accessdate=2010-05-15}}</ref> It was judged that reliable cost estimates for geoengineering had not yet been published.

Chapter 28 of the [[United States National Academy of Sciences|National Academy of Sciences]] report ''Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base'' (1992) defined geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry."<ref name="nas_policy_implications">[http://books.nap.edu/openbook.php?record_id=1605&page=433 Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base] (1992), [[Committee on Science, Engineering, and Public Policy]] (COSEPUP)</ref> They evaluated a range of options to try to give preliminary answers to two questions: can these options work and could they be carried out with a reasonable cost. They also sought to encourage discussion of a third question&nbsp;— what adverse side effects might there be. The following types of option were examined: reforestation, increasing ocean absorption of carbon dioxide (carbon sequestration) and screening out some sunlight. NAS also argued "Engineered countermeasures need to be evaluated but should not be implemented without broad understanding of the direct effects and the potential side effects, the ethical issues, and the risks.".<ref name="nas_policy_implications"/> In July 2011 a report by the [[United States Government Accountability Office]] on geoengineering found that "[c]limate engineering technologies do not now offer a viable response to global climate change."<ref>GAO (2011). Technical status, future directions, and potential responses. July 2011. [http://gao.gov/products/GAO-11-71 GAO-11-71]</ref>

====Carbon dioxide removal====
{{Main|Carbon dioxide removal|Greenhouse gas remediation|Carbon sequestration}}
{{See also|Carbon air capture}}

[[Carbon dioxide removal]] has been proposed as a method of reducing the amount of radiative forcing. A variety of means of artificially capturing and storing carbon, as well as of enhancing natural sequestration processes, are being explored. The main natural process is [[photosynthesis]] by plants and single-celled organisms (see [[biosequestration]]). Artificial processes vary, and concerns have been expressed about the long-term effects of some of these processes.<ref name=RoyalSociety>The Royal Society, (2009) [http://royalsociety.org/displaypagedoc.asp?id=35151 "Geoengineering the climate: science, governance and uncertainty"]. Retrieved 2009-09-12.</ref>

It is notable that the availability of cheap energy and appropriate sites for [[carbon capture and storage|geological storage]] of carbon may make [[carbon dioxide air capture]] viable commercially. It is, however, generally expected that carbon dioxide air capture may be uneconomic when compared to [[carbon capture and storage]] from major sources&nbsp;— in particular, fossil fuel powered power stations, refineries, etc. As in the case of the US [[Kemper Project]] with carbon capture, costs of energy produced will grow significantly. However, captured CO<sub>2</sub> can be used to force more [[crude oil]] out of [[oil field]]s, as [[Statoil]] and [[Royal Dutch Shell|Shell]] have made plans to do.<ref>[https://web.archive.org/web/20090212213143/http://www.forbes.com/feeds/afx/2006/03/08/afx2578203.html Statoil, Shell in plan to raise oil output by injecting {{CO2}} – report], [[AFX News]] via [[Forbes]], March 8, 2006, checked 2009-01-15</ref> CO<sub>2</sub> can also be used in commercial [[greenhouse]]s, giving an opportunity to kick-start the technology. Some attempts have been made to use [[algae]] to capture [[smokestack]] emissions,<ref>{{cite web|url=http://web.mit.edu/erc/spotlights/alg-all.html |title=MIT Energy Research Council: Research Spotlight |publisher=Web.mit.edu |accessdate=2010-08-26}}</ref> notably the [[GreenFuel Technologies Corporation]], who have now shut down operations.<ref>{{cite web|url=http://www.greentechmedia.com/articles/read/greenfuel-technologies-closing-down-4670/ |title=GreenFuel Technologies Closing Down: Greentech Media |publisher=Greentechmedia.com |date=2009-05-13 |accessdate=2010-08-26}}</ref>

====Solar radiation management====
{{Main|Solar radiation management}}
{{See also|Stratospheric aerosol injection (climate engineering)}}
The main purpose of solar radiation management seek to reflect sunlight and thus reduce global warming. The ability of stratospheric [[sulfate aerosols]] to create a [[global dimming]] effect has made them a possible candidate for use in [[climate engineering]] projects.<ref>{{cite journal |url=http://journals.royalsociety.org/content/84j11614488142u8/ |journal=Phil. Trans. R. Soc. A |year=2008 |volume=366 |pages=4039–4056 |title=Global and Arctic climate engineering: numerical model studies |doi=10.1098/rsta.2008.0132 |author1=Launder B. |author2=J.M.T. Thompson |pmid=18757275 |issue=1882 |bibcode=2008RSPTA.366.4039C}}</ref>

===Non-CO<sub>2</sub> greenhouse gases===
CO<sub>2</sub> is not the only GHG relevant to mitigation,<ref>{{cite web|last=Shindell |first=Drew |url=http://www.sciencemag.org/content/335/6065/183 |title=Simultaneously Mitigating Near-Term Climate Change and Improving Human Health and Food Security &#124; Science |publisher=Sciencemag.org |date=2012-01-13 |accessdate=2016-05-06}}</ref> and governments have acted to regulate the emissions of other GHGs emitted by human activities ([[human impact on the environment|anthropogenic]] GHGs). The emissions caps agreed to by most developed countries under the [[Kyoto Protocol]] regulate the emissions of almost all the anthropogenic GHGs.<ref>{{cite journal
|title=The Economics of the Kyoto Protocol
|author=Grubb, M.
|date=July–September 2003
|journal=World Economics
|volume=4
|issue=3
|pages=146–47
|url=http://www.econ.cam.ac.uk/rstaff/grubb/publications/J36.pdf
|format=PDF
|accessdate=2010-03-25
|deadurl=yes
|archiveurl=https://web.archive.org/web/20110717152152/http://www.econ.cam.ac.uk/rstaff/grubb/publications/J36.pdf
|archivedate=2011-07-17
|df=
}}</ref>
These gases are CO<sub>2</sub>, [[methane]] (CH<sub>4</sub>), [[nitrous oxide]] (N<sub>2</sub>O), the [[halocarbon|hydrofluorocarbons]] (HFC), perfluorocarbons (PFC), and [[sulfur hexafluoride]] (SF<sub>6</sub>).

Stabilizing the atmospheric concentrations of the different anthropogenic GHGs requires an understanding of their different physical properties. Stabilization depends both on how quickly GHGs are added to the atmosphere and how fast they are removed. The rate of removal is measured by the atmospheric lifetime of the GHG in question (see the [[greenhouse gas#Global warming potential|main GHG article]] for a list). Here, the lifetime is defined as the time required for a given perturbation of the GHG in the atmosphere to be reduced to 37% of its initial amount.<ref name="meehl stabilizing ghg concentrations"/>
Methane has a relatively short atmospheric lifetime of about 12 years, while N<sub>2</sub>O's lifetime is about 110 years. For methane, a reduction of about 30% below current emission levels would lead to a stabilization in its atmospheric concentration, while for N<sub>2</sub>O, an emissions reduction of more than 50% would be required.<ref name="meehl stabilizing ghg concentrations"/>

[[Methane]] is a significantly more potent greenhouse gas than [[carbon dioxide]] in the amount of heat it can trap, especially in the short term.<ref>{{cite web|title= Methane vs. Carbon Dioxide: A Greenhouse Gas Showdown|url= http://www.onegreenplanet.org/animalsandnature/methane-vs-carbon-dioxide-a-greenhouse-gas-showdown/|website= One Green Planet|accessdate= 2015-11-15}}</ref> Burning one molecule of methane generates one molecule of carbon dioxide, indicating there may be no net benefit in using gas as a fuel source.<ref name="usclimatenetwork.org"/><ref name="epa.gov"/> Reducing the amount of waste methane produced in the first place and moving away from use of gas as a fuel source will have a greater beneficial impact, as might other approaches to productive use of otherwise-wasted methane. In terms of prevention, vaccines are being developed in Australia to reduce the significant global warming contributions from [[methane]] released by livestock via [[flatulence]] and [[eructation]].<ref>[https://www.newscientist.com/article.ns?id=dn6431 Burp vaccine cuts greenhouse gas emissions] ''Rachel Nowak'' for NewScientist September 2004</ref>

Another physical property of the anthropogenic GHGs relevant to mitigation is the different abilities of the gases to trap heat (in the form of [[infrared radiation]]). Some gases are more effective at trapping heat than others, e.g., SF<sub>6</sub> is 22,200 times more effective a GHG than CO<sub>2</sub> on a per-kilogram basis.<ref>{{cite book
|year=2001
|contribution=Halocarbons and related compounds
|title=Technical summary
|series=Climate Change 2001: The physical science basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change
|editor=J.T. Houghton
|publisher=Print version: Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. This version: GRID-Arendal website
|author=Albrittion, D.L.
|url=http://www.grida.no/climate/ipcc_tar/wg1/017.htm#halocarbons
|page=43
|accessdate=2011-06-07
|display-authors=etal
|display-editors=etal
}}</ref>
A measure for this physical property is the [[global warming potential]] (GWP), and is used in the Kyoto Protocol.<ref>{{cite book
|year=2007
|contribution=Definition of "Global Warming Potential"
|title=Annex I: Glossary
|series=Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
|editors=Glossary: A.P.M. Baede. of the main report: S. Solomon
|publisher=Print version: Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. This version: IPCC website
|url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/annexessglossary-e-o.html
|accessdate=2011-06-07|display-editors=etal}}</ref>

Although not designed for this purpose, the [[Montreal Protocol]] has probably benefited climate change mitigation efforts.<ref>{{cite journal
|date=20 March 2007
|journal=PNAS
|volume=104
|issue=12
|pages=4814–19
|author=Velders, G.J.M.
|title=The importance of the Montreal Protocol in protecting climate
|doi=10.1073/pnas.0610328104
|url=http://www.pnas.org/content/104/12/4814
|accessdate=2011-06-07
|bibcode= 2007PNAS..104.4814V
|pmid=17360370
|pmc=1817831
|display-authors=etal
}}</ref>
The Montreal Protocol is an international [[treaty]] that has successfully reduced emissions of [[ozone-depleting substance]]s (for example, [[Chlorofluorocarbon|CFCs]]), which are also greenhouse gases.

==By sector==
[[File:TeslaRoadster-front.jpg|thumb|The [[Tesla Roadster (2008)]] emits no tailpipe emissions, uses [[Li-Ion|lithium ion]] batteries to achieve {{convert|220|mi|abbr=on}} per charge, while also capable of going 0–60 in under 4 seconds.]]
[[File:BikesInAmsterdam 2004 SeanMcClean.jpg|right|thumb|[[Bicycle]]s have almost no [[carbon footprint]] compared to cars, and canal transport may represent a positive option for certain types of freight in the 21st century.<ref>{{cite web|title=The Future of the Canals|url=http://www.canalmuseum.org.uk/education/teacher/lessonplan-future.pdf|publisher=London Canal Museum|accessdate=8 September 2013}}</ref>]]

===Transport===
{{Main|Sustainable transport}}
Transportation emissions account for roughly 1/4 of emissions worldwide, and are even more important in terms of impact in developed nations especially in North America and Australia. Many citizens of countries like the United States and Canada who drive personal cars often, see well over half of their climate change impact stemming from the emissions produced from their cars. Modes of mass transportation such as bus, light rail (metro, subway, etc.), and long-distance rail are far and away the most energy-efficient means of motorized transportation for passengers, able to use in many cases over twenty times less energy per person-distance than a personal automobile. Modern [[efficient energy use|energy-efficient technologies]], such as [[plug-in hybrid]] electric vehicles and [[carbon-neutral fuel|carbon-neutral synthetic gasoline & Jet fuel]] may also help to reduce the consumption of [[petroleum]], land use changes and emissions of [[carbon dioxide]]. Utilizing [[rail transport]], especially electric rail, over the far less efficient [[environmental impact of aviation|air transport]] and [[road transport|truck transport]]
significantly reduces emissions.<ref>{{cite journal
|author= Lowe, Marcia D.
|title= Back on Track: The Global Rail Revival
|date=April 1994
|url =http://www.worldwatch.org/node/872
|accessdate= 2007-02-15}}</ref><ref>{{cite journal
|author= Schwartzman, Peter
|title= TRUCKS VS. TRAINS—WHO WINS?
|url =http://www.thezephyr.com/environ/trucktrain.html
|accessdate= 2007-02-15}}</ref> With the use of electric trains and cars in transportation there is the opportunity to run them with [[low-carbon power]], producing far fewer emissions.

===Urban planning===
{{Main|Urban planning}}

Effective [[urban planning]] to reduce [[urban sprawl|sprawl]] aims to decrease Vehicle Miles Travelled (VMT), lowering emissions from transportation. Personal cars are extremely inefficient at moving passengers, while [[public transport]] and bicycles are many times more efficient (as is the simplest form of human transportation, walking). All of these are encouraged by urban/community planning and are an effective way to reduce greenhouse gas emissions. Between 1982 and 1997, the amount of land consumed for [[urban development]] in the United States increased by 47 percent while the nation's population grew by only 17 percent.<ref>{{cite web
|title=Who Sprawls Most? How Growth Patterns Differ Across the U.S
|url=http://www.brookings.edu/es/urban/publications/fulton.pdf
|first1=William|last1=Fulton
|first2=Rolf|last2=Pendall
|first3=Mai|last3=Nguyen
|first4=Alicia|last4=Harrison
|publisher=[[The Brookings Institution]] Center on Urban and Metropolitan Policy
|location=Washington D.C.
|year=2001
|series=Survey Series}}</ref>
Inefficient [[land use]] development practices have increased infrastructure costs as well as the amount of energy needed for transportation, community services, and buildings.

At the same time, a growing number of citizens and government officials have begun advocating a smarter approach to land use planning. These [[smart growth]] practices include compact community development, multiple transportation choices, mixed land uses, and practices to conserve green space. These programs offer environmental, economic, and quality-of-life benefits; and they also serve to reduce energy usage and greenhouse gas emissions.

Approaches such as [[New Urbanism]] and [[transit-oriented development]] seek to reduce distances travelled, especially by private vehicles, encourage [[public transit]] and make [[walking]] and [[cycling]] more attractive options. This is achieved through "medium-density", [[mixed-use development|mixed-use planning]] and the concentration of housing within walking distance of [[town center]]s and [[transport node]]s.<!--Energy usage comparisons done in the book "Sustainability and Cities" by Peter Newman and Jeff Kentworthy.-->

Smarter growth land use policies have both a direct and indirect effect on energy consuming behavior. For example, transportation energy usage, the number one user of petroleum fuels, could be significantly reduced through more compact and mixed use land development patterns, which in turn could be served by a greater variety of non-automotive based transportation choices.

====Building design====
{{Main|Sustainable architecture|Green building}}

Emissions from [[house|housing]] are substantial,<ref>{{cite web|url=http://www.est.org.uk/myhome/climatechange/stats/homeenvironment/ |title=Energy Saving Trust: Home and the environment |publisher=[[Energy Saving Trust]] |accessdate=2010-08-26}}</ref> and government-supported energy efficiency programmes can make a difference.<ref>{{cite news
|last= Osborne
|first= Hilary
|title= Energy efficiency 'saves £350m a year'
|newspaper= Guardian Unlimited
|date= 2005-08-02
|url= http://money.guardian.co.uk/utilities/story/0,11992,1541051,00.html?gusrc=ticker-103704
|location=London}}</ref>

For institutions of higher learning in the United States, greenhouse gas emissions depend primarily on total area of buildings and secondarily on climate.<ref>{{cite journal|last=Fetcher|first=Ned|title=Effects of climate and institution size on greenhouse gas emissions from colleges and universities in the United States|journal=Sustainability: the Journal of Record|date=December 2009|volume=2|issue=6|pages=362–67|url=http://www.liebertonline.com/doi/abs/10.1089/SUS.2009.9820|accessdate=2 March 2011|doi=10.1089/SUS.2009.9820}}</ref> If climate is not taken into account, annual greenhouse gas emissions due to energy consumed on campuses plus purchased electricity can be estimated with the formula, ''E=aS''<sup>''b''</sup>, where ''a'' =0.001621 metric tonnes of CO<sub>2</sub> equivalent/square foot or 0.0241 metric tonnes of CO<sub>2</sub> equivalent/square meter and ''b''= 1.1354.<ref>{{cite web|title=Greenhouse Gas Emissions of Colleges and Universities|url=http://www.wilkes.edu/pages/4243.asp|accessdate=2 March 2011}}</ref>

New buildings can be constructed using [[passive solar building design]], [[low-energy building]], or [[zero-energy building]] techniques, using [[renewable heat]] sources. Existing buildings can be made more efficient through the use of insulation, high-efficiency appliances (particularly [[hot water heater]]s and [[furnaces]]), [[insulated glazing|double- or triple-glazed gas-filled windows]], external window shades, and building orientation and siting. Renewable heat sources such as [[geothermal heat pump|shallow geothermal]] and [[passive solar]] energy reduce the amount of greenhouse gasses emitted. In addition to designing buildings which are more energy-efficient to heat, it is possible to design buildings that are more energy-efficient to cool by using lighter-coloured, more reflective materials in the development of urban areas (e.g. by painting roofs white) and planting trees.<ref>{{cite web
|first= Arthur H.
|last= Rosenfeld
|first2= Joseph J.
|last2= Romm
|first3= Hashem
|last3= Akbari
|first4= Alan C.
|last4= Lloyd
|work= Painting the Town White – and Green
|title= Technology Review
|date= February–March 1997
|publisher= Massachusetts Institute of Technology
|url= http://eande.lbl.gov/HeatIsland/PUBS/PAINTING/}}</ref><ref>{{cite book|author1=Committee on Science, Engineering |author2=Public Policy|title=Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base |publisher=National Academy Press|place= Washington, D.C.|year=1992|isbn= 0-309-04386-7}}</ref> This saves energy because it cools buildings and reduces the [[urban heat island]] effect thus reducing the use of air conditioning.

===Agriculture===
{{See also|Climate change and agriculture}}
According to the [[EPA]], agricultural [[soil management]] practices can lead to production and emission of [[nitrous oxide]] (N2O), a major [[greenhouse gas]] and air pollutant. Activities that can contribute to {{chem|N|2|O}} emissions include [[fertilizer]] usage, [[irrigation]], and [[tillage]]. The management of soils accounts for over half of the emissions from the Agriculture sector. Cattle livestocks account for one third of emissions, through methane emissions. Manure management and rice cultivation also produce gaseous emissions.<ref>{{cite web|url=http://www3.epa.gov/climatechange/ghgemissions/sources/agriculture.html|title=Agriculture: Sources of Greenhouse Gas Emissions|year=2015|publisher=EPA}}</ref>

Methods that significantly enhance carbon sequestration in soil include [[no-till farming]], residue mulching, [[cover crop]]ping, and [[crop rotation]], all of which are more widely used in [[organic farming]] than in conventional farming.<ref>{{cite web |url=http://www.news.cornell.edu/stories/July05/organic.farm.vs.other.ssl.html |title=Organic farming produces same corn and soybean yields as conventional farms, but consumes less energy and no pesticides, study finds |author=Susan S. Lang |date=13 July 2005 |accessdate=8 July 2008}}</ref><ref>{{cite journal |last1=Pimentel |first1=David |title=Environmental, Energetic, and Economic Comparisons of Organic and Conventional Farming Systems |journal=BioScience |volume=55 |issue=7 |pages=573–82 |year=2005 |doi=10.1641/0006-3568(2005)055[0573:EEAECO]2.0.CO;2 |last2=Hepperly |first2=Paul |last3=Hanson |first3=James |last4=Douds |first4=David |last5=Seidel |first5=Rita}}</ref> Because only 5% of US farmland currently uses no-till and residue mulching, there is a large potential for carbon sequestration.<ref>{{cite journal |doi=10.1126/science.1093079 |title=Ecology: Managing Soil Carbon |year=2004 |last1=Lal |first1=Rattan |journal=Science |volume=304 |issue=5669 |page=393 |pmid=15087532 |last2=Griffin |first2=Michael |last3=Apt |first3=Jay |last4=Lave |first4=Lester |last5=Morgan |first5=M. Granger}}</ref>

A 2015 study found that farming can deplete soil carbon and render soil incapable of supporting life; however, the study also showed that [[conservation farming]] can protect carbon in soils, and repair damage over time.<ref>{{cite journal|url=https://eos.org/research-spotlights/conservation-farming-shown-to-protect-carbon-in-soil|title=Conservation Farming Shown to Protect Carbon in Soil|journal=Journal of Geophysical Research: Biogeosciences|authors=A. N. (Thanos) Papanicolaou, Kenneth M. Wacha, Benjamin K. Abban, Christopher G. Wilson, Jerry L. Hatfield, Charles O. Stanier, Timothy R. Filley|year=2015|doi=10.1002/2015JG003078|volume=120|issue=11|pages=2375–2401|bibcode=2015JGRG..120.2375P}}</ref>

The farming practise of [[cover crop]]s has been recognized as climate-smart agriculture by the [[White House]].<ref>{{cite news|url=https://www.nytimes.com/2016/02/07/business/cover-crops-a-farming-revolution-with-deep-roots-in-the-past.html?_r=0|publisher=The New York Times|title=Cover Crops, a Farming Revolution With Deep Roots in the Past|year=2016}}</ref>

In Europe the estimation of the current 0–30&nbsp;cm SOC stock of agricultural soils was 17.63&nbsp;Gt.<ref>{{cite journal|last=Lugato|first=Emanuele|last2=Panagos|first2=Panos|last3=Bampa|first3=Francesca|last4=Jones|first4=Arwyn|last5=Montanarella|first5=Luca|date=2014-01-01|title=A new baseline of organic carbon stock in European agricultural soils using a modelling approach|url=http://onlinelibrary.wiley.com/doi/10.1111/gcb.12292/abstract|journal=Global Change Biology|language=en|volume=20|issue=1|pages=313–326|doi=10.1111/gcb.12292|issn=1365-2486|bibcode=2014GCBio..20..313L}}</ref> In a subsequent study, authors estimated the best management practices to mitigate soil organic carbon: conversion of arable land to grassland (and vice versa), straw incorporation, reduced tillage, straw incorporation combined with reduced tillage, ley cropping system and cover crops.<ref>{{cite journal|last=Lugato|first=Emanuele|last2=Bampa|first2=Francesca|last3=Panagos|first3=Panos|last4=Montanarella|first4=Luca|last5=Jones|first5=Arwyn|date=2014-11-01|title=Potential carbon sequestration of European arable soils estimated by modelling a comprehensive set of management practices|url=http://onlinelibrary.wiley.com/doi/10.1111/gcb.12551/abstract|journal=Global Change Biology|language=en|volume=20|issue=11|pages=3557–3567|doi=10.1111/gcb.12551|issn=1365-2486|bibcode=2014GCBio..20.3557L}}</ref>

===Societal controls===
{{Main|Personal carbon credits}}

Another method being examined is to make carbon a new currency by introducing tradeable "[[personal carbon credits]]". The idea being it will encourage and motivate individuals to reduce their 'carbon footprint' by the way they live. Each citizen will receive a free annual quota of carbon that they can use to travel, buy food, and go about their business. It has been suggested that by using this concept it could actually solve two problems; pollution and poverty, old age pensioners will actually be better off because they fly less often, so they can cash in their quota at the end of the year to pay heating bills and so forth.{{citation needed|reason=previous source deadlink|date=April 2009}}

====Population====
[[File:Population density countries 2017 world map, people per sq km.svg|thumb|400px|[[Population density]] by country]]
Various organizations promote [[population control]] as a means for mitigating global warming.<ref>[http://www.unfpa.org/swp/2009/en/ch6.shtml Facing a changing world: women, population and climate], United Nations Population Fund</ref><ref>[http://www.sierraclub.org/population/reports/globalwarming.asp Population and Global Warming Factsheet] from Sierra Club</ref><ref>[http://www.nwf.org/popandenvironment/globalwarming.cfm Population and Global Warming] National Wild Life Federation</ref><ref>[http://www.populationconnection.org/site/DocServer/Global_Warming.pdf?docID=286 Population and the Environment Fact Sheet] Population Connection</ref><ref>[http://www.populationconnection.org/site/PageServer?pagename=about_us Population Connection] Statement of Policy</ref> Proposed measures include improving access to [[family planning]] and [[reproductive health]] care and information, reducing [[natalistic politics]], public education about the consequences of continued population growth, and improving access of women to education and economic opportunities.

Population control efforts are impeded by there being somewhat of a taboo in some countries against considering any such efforts.<ref>[http://www.bmj.com/cgi/content/full/315/7120/1441 To the point of farce: a martian view of the hardinian taboo—the silence that surrounds population control] Maurice King, Charles Elliott BMJ</ref> Also, various religions [[religious views on birth control|discourage or prohibit]] some or all forms of [[birth control]].

Population size has a different per capita effect on global warming in different countries, since the per capita production of anthropogenic greenhouse gases varies greatly by country.<ref>[http://www.sierraclub.org/population/factsheets/pop_and_globalwarming.asp Who is Heating Up the Planet? A Closer Look at Population and Global Warming] from Sierra Club</ref>

==Costs and benefits==
{{Main|Economics of climate change mitigation}}

===Costs===
The [[Stern Review]] proposes stabilising the concentration of greenhouse-gas emissions in the atmosphere at a maximum of 550ppm CO<sub>2</sub>e by 2050. The Review estimates that this would mean cutting total greenhouse-gas emissions to three quarters of 2007 levels. The Review further estimates that the cost of these cuts would be in the range −1.0 to +3.5% of World [[GDP]], (i.e. [[Gross world product|GWP]]), with an average estimate of approximately 1%.<ref name="stern"/> Stern has since revised his estimate to 2% of GWP.<ref>{{cite news |url=https://www.theguardian.com/environment/2008/jun/26/climatechange.scienceofclimatechange |title=Cost of tackling global climate change has doubled, warns Stern |first= Juliette |last=Jowit |first2= Patrick |last2=Wintour |newspaper=[[The Guardian]] |date=26 June 2008 |location=London}}</ref> For comparison, the Gross World Product (GWP) at [[purchasing power parity|PPP]] was estimated at $74.5 trillion in 2010,<ref>{{cite web
|title= CIA World Factbook |publisher= US [[CIA]] |date= 18 Oct 2011
|url= https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html
|accessdate= 21 Oct 2011}}</ref> thus 2% is approximately $1.5 trillion. The Review emphasises that these costs are contingent on steady reductions in the cost of low-carbon technologies. Mitigation costs will also vary according to how and when emissions are cut: early, well-planned action will minimise the costs.<ref name="stern">Stern, N. (2006). ''Stern Review on the Economics of Climate Change: Part III: The Economics of Stabilisation.'' HM Treasury, London: http://hm-treasury.gov.uk/sternreview_index.htm</ref>

One way of estimating the cost of reducing emissions is by considering the likely costs of potential technological and output changes. Policy makers can compare the [[marginal abatement costs]] of different methods to assess the cost and amount of possible abatement over time. The marginal abatement costs of the various measures will differ by country, by sector, and over time.<ref name="stern"/>

===Benefits===
[[File:Extreme weather in the US 1980-2011.png|thumb|350px|right|Total extreme weather cost and number of events costing more than $1 billion in the United States from 1980 to 2011]]

Yohe ''et al.'' (2007) assessed the literature on sustainability and climate change.<ref>{{cite book
|year=2007
|title=Executive summary. In (book chapter): Perspectives on climate change and sustainability. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (M.L. Parry ''et al''., (eds.))
|publisher=Print version: Cambridge University Press, Cambridge, UK, and New York, NY, US. Web version: IPCC website
|isbn=978-0-521-88010-7
|author=Yohe, G.W.
|url=http://www.ipcc.ch/publications_and_data/ar4/wg2/en/ch20s20-es.html
|accessdate=2010-05-15|display-authors=etal}}</ref> With high confidence, they suggested that up to the year 2050, an effort to cap greenhouse gas (GHG) emissions at 550&nbsp;ppm would benefit [[developing countries]] significantly. This was judged to be especially the case when combined with enhanced adaptation. By 2100, however, it was still judged likely that there would be significant [[effects of global warming]]. This was judged to be the case even with aggressive mitigation and significantly enhanced [[adaptive capacity]].

===Sharing===
One of the aspects of mitigation is how to share the costs and benefits of mitigation policies. There is no scientific consensus over how to share these costs and benefits (Toth ''et al.'', 2001).<ref>{{cite book
|year= 2001
|title= 10.4.7 Emerging Conclusions with Respect to Policy-relevant Scientific Questions. In (book chapter): Decision-making Frameworks. In: Climate Change 2001: Mitigation. Contribution of Working Group III to the Third Assessment Report of the Intergovernmental Panel on Climate Change (B. Metz ''et al''. Eds.)
|publisher= Print version: Cambridge University Press, Cambridge, UK, and New York, NY, US. This version: GRID-Arendal website
|author= Toth, F.L.
|isbn= 978-0-521-01502-8
|url= http://www.grida.no/climate/ipcc_tar/wg3/449.htm
|accessdate= 2010-01-10
|display-authors= etal
|deadurl= yes
|archiveurl= https://web.archive.org/web/20090805210205/http://www.grida.no/climate/ipcc_tar///wg3/449.htm
|archivedate= 2009-08-05
|df =
}}</ref> In terms of the politics of mitigation, the UNFCCC's ultimate objective is to stabilize concentrations of GHG in the atmosphere at a level that would [[Avoiding Dangerous Climate Change|prevent "dangerous" climate change]] (Rogner ''et al.'', 2007).<ref>{{cite book
|year=2007
|author=Rogner, H.-H.
|title=Executive Summary. In (book chapter): Introduction. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (B. Metz ''et al.'' (eds))
|url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch1s1-es.html
|publisher=Print version: Cambridge University Press, Cambridge, United Kingdom and New York, NY. Web version: IPCC website
|isbn=978-0-521-88011-4
|accessdate=2010-05-05|display-authors=etal}}</ref>

GHG emissions are an important correlate of wealth, at least at present (Banuri ''et al.'', 1996, pp.&nbsp;91–92).<ref name=banuri>{{cite book
|year=1996
|author=Banuri, T.
|title=Equity and Social Considerations. In: Climate Change 1995: Economic and Social Dimensions of Climate Change. Contribution of Working Group III to the Second Assessment Report of the Intergovernmental Panel on Climate Change (J.P. Bruce ''et al''. Eds.)
|publisher=This version: Printed by Cambridge University Press, Cambridge, UK, and New York, NY, US. PDF version: IPCC website
|format=PDF
|url=http://www.ipcc.ch/ipccreports/sar/wg_III/ipcc_sar_wg_III_full_report.pdf
|isbn=978-0-521-56854-8
|doi=10.2277/0521568544|display-authors=etal}}</ref> Wealth, as measured by per capita income (i.e., income per head of population), varies widely between different countries. Activities of the poor that involve emissions of GHGs are often associated with basic needs, such as [[heating]] to stay tolerably warm. In richer countries, emissions tend to be associated with things like [[car]]s, [[central heating]], etc. The impacts of cutting emissions could therefore have different impacts on human [[welfare economics|welfare]] according to wealth.

====Distributing emissions abatement costs====
There have been different proposals on how to allocate responsibility for cutting emissions (Banuri ''et al.'', 1996, pp.&nbsp;103–105):<ref name=banuri/>
*'''[[Egalitarianism]]''': this system interprets the problem as one where each person has equal rights to a global resource, i.e., polluting the atmosphere.
*'''Basic needs''': this system would have emissions allocated according to basic needs, as defined according to a minimum level of [[consumption (economics)|consumption]]. Consumption above basic needs would require countries to buy more emission rights. From this viewpoint, developing countries would need to be at least as well off under an emissions control regime as they would be outside the regime.
*'''Proportionality and polluter-pays principle''': Proportionality reflects the ancient [[Aristotelianism|Aristotelian]] principle that people should receive in proportion to what they put in, and pay in proportion to the damages they cause. This has a potential relationship with the "polluter-pays principle", which can be interpreted in a number of ways:
**''Historical responsibilities'': this asserts that allocation of emission rights should be based on patterns of past emissions. Two-thirds of the stock of GHGs in the atmosphere at present is due to the past actions of developed countries (Goldemberg ''et al.'', 1996, p.&nbsp;29).<ref name=goldemberg>{{cite book
|year=1996
|author=Goldemberg, J.
|title=Introduction: scope of the assessment. In: Climate Change 1995: Economic and Social Dimensions of Climate Change. Contribution of Working Group III to the Second Assessment Report of the Intergovernmental Panel on Climate Change (J.P. Bruce ''et al''. Eds.)
|publisher=This version: Printed by Cambridge University Press, Cambridge, UK, and New York, NY, US. Web version: IPCC website
|format=PDF
|url=http://www.ipcc.ch/ipccreports/sar/wg_III/ipcc_sar_wg_III_full_report.pdf
|isbn=978-0-521-56854-8
|doi=10.2277/0521568544|display-authors=etal}}</ref>
**''Comparable burdens and ability to pay'': with this approach, countries would reduce emissions based on comparable burdens and their ability to take on the costs of reduction. Ways to assess burdens include monetary costs per head of population, as well as other, more complex measures, like the [[UNDP]]'s [[Human Development Index]].
**''[[Willingness to pay]]'': with this approach, countries take on emission reductions based on their ability to pay along with how much they benefit from reducing their emissions.

====Specific proposals====
*'''Ad hoc''': Lashof (1992) and Cline (1992) (referred to by Banuri ''et al.'', 1996, p.&nbsp;106),<ref name=banuri/> for example, suggested that allocations based partly on [[GNP]] could be a way of sharing the burdens of emission reductions. This is because GNP and economic activity are partially tied to carbon emissions.
*'''Equal per capita entitlements''': this is the most widely cited method of distributing abatement costs, and is derived from egalitarianism (Banuri ''et al.'', 1996, pp.&nbsp;106–107). This approach can be divided into two categories. In the first category, emissions are allocated according to national population. In the second category, emissions are allocated in a way that attempts to account for historical (cumulative) emissions.
*'''Status quo''': with this approach, historical emissions are ignored, and current emission levels are taken as a status quo right to emit (Banuri ''et al.'', 1996, p.&nbsp;107). An analogy for this approach can be made with [[fishery|fisheries]], which is a common, limited resource. The analogy would be with the atmosphere, which can be viewed as an exhaustible [[natural resource]] (Goldemberg ''et al.'', 1996, p.&nbsp;27).<ref name=goldemberg/> In [[international law]], one state recognized the long-established use of another state's use of the fisheries resource. It was also recognized by the state that part of the other state's economy was dependent on that resource.

==Governmental and intergovernmental action==
{{Main|Politics of global warming}}
{{Reduced pull quote|1=right
|2=Bringing down emissions of greenhouse gases asks a good deal of people, not least that they accept the science of climate change. It requires them to make sacrifices today so that future generations will suffer less, and to weigh the needs of people who are living far away.
|3=''[[The Economist]]''|4=28 November 2015<ref>Article [https://www.economist.com/news/special-report/21678962-how-farmers-poor-countries-are-responding-climate-change-if-you-cant-stand-heat "Adaptation. If you can't stand the heat"], ''[[The Economist]]'', special report on "Climate change", 28 November 2015, page 10-12.</ref>}}

Many countries, both developing and developed, are aiming to use cleaner technologies (World Bank, 2010, p.&nbsp;192).<ref>{{cite book
|year= 2010
|author= World Bank
|title= World Development Report 2010: Development and Climate Change
|publisher= The International Bank for Reconstruction and Development / The World Bank, 1818 H Street NW, Washington DC 20433
|url= http://go.worldbank.org/BKLQ9DSDU0
|isbn= 978-0-8213-7987-5
|doi= 10.1596/978-0-8213-7987-5
|accessdate= 2010-04-06
|deadurl= yes
|archiveurl= https://web.archive.org/web/20100410171605/http://go.worldbank.org/BKLQ9DSDU0
|archivedate= 2010-04-10
|df =
}}</ref> Use of these technologies aids mitigation and could result in substantial reductions in CO<sub>2</sub> emissions. Policies include targets for emissions reductions, increased use of renewable energy, and increased energy efficiency. It is often argued that the results of climate change are more damaging in poor nations, where infrastructures are weak and few social services exist. The [[Commitment to Development Index]] is one attempt to analyze rich country policies taken to reduce their disproportionate use of the global commons. Countries do well if their greenhouse gas emissions are falling, if their gas taxes are high, if they do not subsidize the fishing industry, if they have a low fossil fuel rate per capita, and if they control imports of illegally cut tropical timber.

===Kyoto Protocol===
{{Main|Kyoto Protocol}}

The main current international agreement on combating climate change is the [[Kyoto Protocol]]. On the 11th of December 1997 it was implemented by the 3rd conference of parties, which was coming together in kyoto, which came into force on 16 February 2005. The Kyoto Protocol is an [[wikt:Amendment|amendment]] to the United Nations Framework Convention on Climate Change (UNFCCC). [[List of Kyoto Protocol signatories|Countries that have ratified this protocol]] have committed to reduce their emissions of [[carbon dioxide]] and five other greenhouse gases, or engage in [[emissions trading]] if they maintain or increase emissions of these gases. For Kyoto reporting, governments are obliged to be told on the present state of the countries forests and the related ongoing processes.

===Temperature targets===
[[File:Limiting global warming to 2 degrees Celsius - options to reduce greenhouse gas emissions (PBL)EN.svg|thumb|400px|alt=Refer to caption and image description|The graph on the right shows three "pathways" to meet the UNFCCC's 2&nbsp;°C target, labelled "global technology", "decentralised solutions", and "consumption change". Each pathway shows how various measures (e.g., improved energy efficiency, increased use of renewable energy) could contribute to emissions reductions. Image credit: PBL [[Netherlands Environmental Assessment Agency]].<ref>{{citation
|date=15 June 2012
|author=PBL Netherlands Environment Agency
|editor=van Vuuren, D. |editor2=M. Kok
|title=Roads from Rio+20
|chapter=Figure 6.14, in: Chapter 6: The energy and climate challenge
|url=http://www.pbl.nl/sites/default/files/cms/publicaties/pbl-2012-roads-from-rio-pathways-to-achieve-global-sustainability-goals-by-2050_0.pdf
|isbn=978-90-78645-98-6}}, p. 177, Report no: 500062001. [http://www.pbl.nl/en/publications/2012/roads-from-rio20 Report website.]</ref>]]

Actions to mitigate climate change are sometimes based on the goal of achieving a particular temperature target. One of the targets that has been suggested is to limit the future increase in global mean temperature (global warming) to below 2&nbsp;°C, relative to the pre-industrial level.<ref name="Jaeger, C.C., and J. Jaeger 2011 15–26">{{citation
|author1=Jaeger, C.C. |author2=J. Jaeger
|title=Three views of two degrees
|work=Regional Environmental Change
|volume=11
|issue=1
|url=http://www.pik-potsdam.de/members/cjaeger/publications/2010-2000-1/three%20views.pdf
|pages=15–26
|year=2011
|doi=10.1007/s10113-010-0190-9
|issn=1436-3798
|publisher=Springer-Verlag
}}</ref><ref name="Stockholm Environment Institute">{{citation
|editor=Rijsberman, F.J. |editor2=R.J. Stewart
|year=1990
|title=Targets and Indicators of Climate Change
|publisher=Stockholm Environment Institute
|location=Stockholm, Sweden
|isbn=91-88116-21-2
|url=http://www.sei-international.org/publications?pid=465
}}. [http://www.climateemergencyinstitute.com/uploads/1990_one.pdf Summary available] from the Climate Emergency Institute.</ref> The 2&nbsp;°C target was adopted in 2010 by Parties to the United Nations Framework Convention on Climate Change.<ref name="UNFCCC">{{citation
|date=15 March 2011
|author=UNFCCC
|title=FCCC/CP/2010/7/Add.1: Report of the Conference of the Parties on its sixteenth session, held in Cancun from 29 November to 10 December 2010. Addendum. Part two: Action taken by the Conference of the Parties at its sixteenth session
|publisher=UN Office
|location=Geneva, Switzerland
|url=http://maindb.unfccc.int/library/view_pdf.pl?url=http://unfccc.int/resource/docs/2010/cop16/eng/07a01.pdf
}}. [http://unfccc.int/documentation/documents/advanced_search/items/6911.php?priref=600006173 Available] as a PDF in English, Spanish, French, Arabic, and Russian.</ref> Most countries of the world are Parties to the UNFCCC.<ref name="unfccc.int">{{citation
|url=http://unfccc.int/essential_background/items/6031.php
|title=Essential Background
|author=UNFCCC
|publisher=UNFCCC
|date=3 May 2012
}}</ref> The target had been adopted in 1996 by the [[Council of the European Union|European Union Council]].<ref>Oliver Geden (2013), [http://www.swp-berlin.org/fileadmin/contents/products/research_papers/2013_RP05_gdn.pdf Modifying the 2°C Target. Climate Policy Objectives in the Contested Terrain of Scientific Policy Advice, Political Preferences, and Rising Emissions], [[German Institute for International and Security Affairs|SWP]] Research Paper 5/13</ref>

; Feasibility of 2&nbsp;°C
Temperatures have increased by 0.8&nbsp;°C compared to the pre-industrial level, and another 0.5–0.7&nbsp;°C is already [[climate commitment|committed]].<ref>Oliver Geden (2010), [http://www.swp-berlin.org/fileadmin/contents/products/comments/2010C19_gdn_ks.pdf What Comes After the Two-Degree Target?], [[German Institute for International and Security Affairs|SWP]] Comments 19</ref> The 2&nbsp;°C rise is typically associated in [[climate model]]s with a [[carbon dioxide equivalent]] concentration of 400–500 [[parts per million|ppm]] by volume; the current (January 2015) level of carbon dioxide alone is 400 ppm by volume, and rising at 1–3 ppm annually. Hence, to avoid a very likely breach of the 2&nbsp;°C target, CO<sub>2</sub> levels would have to be stabilised very soon; this is generally regarded as unlikely, based on current programs in place to date.<ref>{{cite web
|title= EU climate change target "unfeasible"
|publisher= EurActiv.com
|date= 2006-02-01
|url= http://www.euractiv.com/Article?tcmuri=tcm:29-152154-16&type=News
|accessdate= 2007-02-21}}</ref><ref>{{cite news
|url=https://www.theguardian.com/environment/2009/apr/14/global-warming-target-2c
|title=World will not meet 2C warming target, climate change experts agree
|publisher=Guardian News and Media Limited
|last=Adam
|first=David
|date=14 April 2009
|accessdate=2009-04-14
|location=London}}</ref> The importance of change is illustrated by the fact that world economic energy efficiency is improving at only half the rate of world [[economic growth]].<ref>[[United States Department of Energy]] [http://www.eia.doe.gov/emeu/cabs/carbonemiss/chapter1.html World Trends] {{webarchive|url=https://web.archive.org/web/20070608100643/http://www.eia.doe.gov/emeu/cabs/carbonemiss/chapter1.html |date=2007-06-08}}</ref>

; Views in the literature
There is disagreement among experts over whether or not the 2&nbsp;°C target can be met.<ref>Oppenheimer, M., ''et al.'', Section 19.7.2: Limits to Mitigation, in: [http://ipcc-wg2.gov/AR5/images/uploads/WGIIAR5-Chap19_FGDall.pdf Chapter 19: Emergent risks and key vulnerabilities] (archived [https://web.archive.org/web/20140701114626/http://ipcc-wg2.gov/AR5/images/uploads/WGIIAR5-Chap19_FGDall.pdf July 8 2014]), pp. 49–50, in {{harvnb|IPCC AR5 WG2 A|2014}}</ref><ref>Oliver Geden/Silke Beck: [http://www.nature.com/nclimate/journal/v4/n9/full/nclimate2309.html ''Renegotiating the global climate stabilization target''.] In: Nature Climate Change, 4, 2014, pp. 747–48</ref> For example, according to Anderson and Bows (2011),<ref>Anderson, K. & Bows, A., 2011. [http://rsta.royalsocietypublishing.org/content/369/1934/20.full.pdf+html Beyond 'dangerous' climate change: emission scenarios for a new world]. Philos. Trans. Royal Society A.</ref> "there is little to no chance" of meeting the target. On the other hand, according to Alcamo ''et al.'' (2013):<ref>{{harvnb|Alcamo|others|2013|p=xi}}</ref>
*Policies adopted by parties to the UNFCCC are too weak to meet a 2 or 1.5&nbsp;°C target. However, these targets might still be achievable if more stringent mitigation policies are adopted immediately.
*Cost-effective 2&nbsp;°C scenarios project annual global greenhouse gas emissions to peak before the year 2020, with deep cuts in emissions thereafter, leading to a reduction in 2050 of 41% compared to 1990 levels.<ref>{{harvnb|Alcamo|others|2013|pp=xiii–xiv}}</ref>

; Discussion on other targets
Scientific analysis can provide information on the impacts of climate change and associated policies, such as reducing GHG emissions. However, deciding what policies are best requires value judgements.<ref name="wg 2 ch19 dangerous climate change"/> For example, limiting global warming to 1&nbsp;°C relative to pre-industrial levels may help to reduce climate change damages more than a 2&nbsp;°C limit.<ref>"Implication for Carbon Emissions Target," in: {{harvnb|Hansen|others|2013|p=15}}</ref> However, a 1&nbsp;°C limit may be more costly to achieve than a 2&nbsp;°C limit.<ref>"4. Discussion and conclusions," in: {{harvnb|Luderer|others|2013|p=6}}</ref>

According to some analysts, the 2&nbsp;°C "guardrail" is inadequate for the needed degree and timeliness of mitigation.<ref name="existing policies inadequate"/> On the other hand, some economic studies suggest more modest mitigation policies.<ref name="van vuuren mitigation policy"/> For example, the emissions reductions proposed by Nordhaus (2010)<ref name="nordhaus 2010 cba">Figure 3, in: {{harvnb|Nordhaus|2010|p=4}}</ref> might lead to global warming (in the year 2100) of around 3&nbsp;°C, relative to pre-industrial levels.

; Official long-term target of 1.5&nbsp;°C
In 2015, two official UNFCCC scientific expert bodies came to the conclusion that, "in some regions and vulnerable ecosystems, high risks are projected even for warming above 1.5°C".<ref>{{cite web
|title= Report on the structured expert dialogue on the 2013–2015 review
|publisher= UNFCCC, Subsidiary Body for Scientific and Technological Advice & Subsidiary Body for Implementation
|date= 2015-04-04
|url= http://unfccc.int/resource/docs/2015/sb/eng/inf01.pdf
|accessdate= 2016-06-21}}</ref> This expert position was, together with the strong diplomatic voice of the poorest countries and the island nations in the Pacific, the driving force leading to the decision of the [[2015 United Nations Climate Change Conference|Paris Conference]] 2015, to lay down this 1.5&nbsp;°C long-term target on top of the existing 2&nbsp;°C goal.<ref>{{cite web
|title= 1.5°C temperature limit – key facts
|publisher= Climate Analytics
|url= http://climateanalytics.org/hot-topics/1-5c-key-facts.html
|accessdate= 2016-06-21}}</ref>

===Encouraging use changes===

====Emissions tax====
{{See also|carbon tax|energy tax|fee and dividend}}

An emissions tax on greenhouse gas emissions requires individual emitters to pay a fee, charge or tax for every tonne of greenhouse gas released into the atmosphere.<ref name="gupta emissions tax">{{cite book
|year=2007
|contribution=13.2.1.2 Taxes and charges
|title=Policies, instruments, and co-operative arrangements
|series=Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
|editor=B. Metz
|publisher=Print version: Cambridge University Press, Cambridge, UK, and New York, NY. This version: IPCC website
|author=Gupta, S.
|url=http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch13s13-2-1-2.html
|accessdate=2010-03-18|display-authors=etal|display-editors=etal}}</ref> Most environmentally related taxes with implications for greenhouse gas emissions in OECD countries are levied on energy products and motor vehicles, rather than on CO<sub>2</sub> emissions directly.<ref name="gupta emissions tax"/>

Emission taxes can be both cost-effective and environmentally effective.<ref name="gupta emissions tax"/> Difficulties with emission taxes include their potential unpopularity, and the fact that they cannot guarantee a particular level of emissions reduction.<ref name="gupta emissions tax"/> Emissions or energy taxes also often fall disproportionately on lower income classes. In developing countries, institutions may be insufficiently developed for the collection of emissions fees from a wide variety of sources.<ref name="gupta emissions tax"/>

====Subsidies====
According to [[Mark Z. Jacobson]], a program of subsidization balanced against expected flood costs could pay for conversion to 100% renewable power by 2030.<ref name="wws-review">{{cite journal |last1= Jacobson |first1= M.Z. |year= 2009 |title= Review of solutions to global warming, air pollution, and energy security |url= http://www.stanford.edu/group/efmh/jacobson/PDF%20files/ReviewSolGW09.pdf |format= PDF |journal= Energy and Environmental Science |volume= 2 |issue= 2 |pages= 148–73 |doi= 10.1039/b809990c}}{{dead link|date=November 2017 |bot=InternetArchiveBot |fix-attempted=yes}}</ref> Jacobson, and his colleague Mark Delucchi, suggest that the cost to generate and transmit power in 2020 will be less than 4 cents per kilowatt hour (in 2007 dollars) for wind, about 4 cents for wave and hydroelectric, from 4 to 7 cents for geothermal, and 8 cents per kWh for solar, fossil, and nuclear power.<ref name=wws>{{cite journal|last1= [[Mark Z. Jacobson|Jacobson]]|first1= M.Z.|last2= Delucchi|first2= M.A.|year= 2009|title= A Plan to Power 100 Percent of the Planet with Renewables" (originally published as "A Path to Sustainable Energy by 2030")|url= http://www.scientificamerican.com/article.cfm?id=a-path-to-sustainable-energy-by-2030|journal= [[Scientific American]]|volume= 301|issue= 5 |pages= 58–65|pmid= 19873905|doi=10.1038/scientificamerican1109-58|bibcode= 2009SciAm.301e..58J}}</ref>

====Investment====
{{See also|Fossil fuel divestment}}

Another indirect method of encouraging uses of renewable energy, and pursue sustainability and environmental protection, is that of prompting investment in this area through legal means, something that is already being done at national level as well as in the field of international investment.<ref>{{cite journal|last1=Farah|first1=Paolo Davide|title=Sustainable Energy Investments and National Security: Arbitration and Negotiation Issues|journal=Journal of World Energy Law and Business|date=2015|volume=8|issue=6|ssrn=2695579|accessdate=}}</ref>

====Carbon emissions trading====
{{Main|Carbon emissions trading}}

With the creation of a [[market (economics)|market]] for [[carbon emissions trading|trading carbon dioxide emissions]] within the Kyoto Protocol, it is likely that London financial markets will be the centre for this potentially highly lucrative business; the [[NYSE|New York]] and [[Chicago]] stock markets may have a lower trade volume than expected as long as the US maintains its rejection of the [[Kyoto Protocol|Kyoto]].<ref>[http://observer.guardian.co.uk/focus/story/0,,1509761,00.html How high-pressure politics threatens action on climate] The Observer June 2005</ref>

However, emissions trading may delay the phase-out of fossil fuels.<ref>''StoryOfStuff.com'' (2009) [http://storyofstuff.com/capandtrade/ "The Story of Cap and Trade"]</ref>

In the north-east United States, a successful cap and trade program has shown potential for this solution.<ref>{{cite web|url=http://scienceprogress.org/2013/02/success-of-northeast-cap-and-trade-system-shows-market-based-climate-policy-is-well-within-reach/|title=Success of Northeast Cap-and-Trade System Shows Market-Based Climate Policy Is Well Within Reach|publisher=}}</ref>

The [[European Union Emission Trading Scheme]] (EU ETS)<ref>[http://ec.europa.eu/environment/climat/emission.htm Emission Trading Scheme (EU ETS)] from ''ec.europa.eu''</ref> is the largest multi-national, greenhouse gas emissions trading scheme in the world. It commenced operation on 1 January 2005, and all 28 member states of the [[European Union]] participate in the scheme which has created a new market in carbon dioxide allowances estimated at 35&nbsp;billion Euros (US$43&nbsp;billion) per year.<ref>[http://www.opendemocracy.net/globalization-climate_change_debate/2570.jsp The $20,000,000,000,000 question] ''Robins, Nick'' for Opendemocracy</ref> The [[Chicago Climate Exchange]] was the first (voluntary) emissions market, and is soon to be followed by Asia's first market ([[Asia Carbon Exchange]]). A total of 107 million metric tonnes of carbon dioxide equivalent have been exchanged through projects in 2004, a 38% increase relative to 2003 (78 Mt CO<sub>2</sub>e).<ref>[http://carbonfinance.org/docs/CarbonMarketStudy2005.pdf State and Trends of the Carbon Market] International Emissions Trading Association 2005</ref>

Twenty three [[multinational corporation]]s have come together in the [[G8 Climate Change Roundtable]], a business group formed at the January 2005 [[World Economic Forum]]. The group includes [[Ford Motor Company|Ford]], [[Toyota]], [[British Airways]], and [[BP]]. On 9 June 2005 the Group published a statement<ref>[http://www.weforum.org/pdf/g8_climatechange.pdf Statement of G8 Climate Change Roundtable] {{webarchive |url=https://web.archive.org/web/20130508123035/http://www.weforum.org/pdf/g8_climatechange.pdf |date=May 8, 2013}} Convened by the World Economic Forum June 2005</ref> stating that there was a need to act on climate change and claiming that market-based solutions can help. It called on governments to establish "clear, transparent, and consistent price signals" through "creation of a long-term policy framework" that would include all major producers of greenhouse gases.

The [[Regional Greenhouse Gas Initiative]] is a proposed carbon trading scheme being created by nine North-eastern and Mid-Atlantic [[United States|American]] states; [[Connecticut]], [[Delaware]], [[Maine]], [[Massachusetts]], [[New Hampshire]], [[New Jersey]], [[New York (state)|New York]], [[Rhode Island]], and [[Vermont]]. The scheme was due to be developed by April 2005 but has not yet been completed.

===Implementation===
Implementation puts into effect climate change mitigation strategies and targets. These can be targets set by international bodies or voluntary action by individuals or institutions. This is the most important, expensive and least appealing aspect of environmental governance.<ref name="Evans">Evans. J (forthcoming 2012) Environmental Governance, Routledge, Oxon</ref>

====Funding====
Implementation requires funding sources but is often beset by disputes over who should provide funds and under what conditions.<ref name="Evans"/> A lack of funding can be a barrier to successful strategies as there are no formal arrangements to finance climate change development and implementation.<ref name="IHDP">Biesbroek. G.R, Termeer. C.J.A.M, Kabat. P, Klostermann.J.E.M (unpublished) Institutional governance barriers for the development and implementation of climate adaptation strategies, Working paper for the International Human Dimensions Programme (IHDP) conference "Earth System Governance: People, Places, and the Planet", December 2–4, Amsterdam, the Netherlands</ref> Funding is often provided by nations, groups of nations and increasingly NGO and private sources. These funds are often channelled through the Global Environmental Facility (GEF). This is an environmental funding mechanism in the World Bank which is designed to deal with global environmental issues.<ref name="Evans"/> The GEF was originally designed to tackle four main areas: biological diversity, climate change, international waters and ozone layer depletion, to which land degradation and persistent organic pollutant were added. The GEF funds projects that are agreed to achieve global environmental benefits that are endorsed by governments and screened by one of the GEF's implementing agencies.<ref>Mee. L. D, Dublin. H. T, Eberhard. A. A (2008) Evaluating the Global Environment Facility: A goodwill gesture or a serious attempt to deliver global benefits?, Global Environmental Change 18, 800–810</ref>

====Problems====
There are numerous issues which result in a current perceived lack of implementation.<ref name="Evans"/> It has been suggested that the main barriers to implementation are Uncertainty, Fragmentation, Institutional void, Short time horizon of policies and politicians and Missing motives and willingness to start adapting. The relationships between many climatic processes can cause large levels of uncertainty as they are not fully understood and can be a barrier to implementation. When information on climate change is held between the large numbers of actors involved it can be highly dispersed, context specific or difficult to access causing fragmentation to be a barrier. Institutional void is the lack of commonly accepted rules and norms for policy processes to take place, calling into question the legitimacy and efficacy of policy processes. The Short time horizon of policies and politicians often means that climate change policies are not implemented in favour of socially favoured societal issues. Statements are often posed to keep the illusion of political action to prevent or postpone decisions being made. Missing motives and willingness to start adapting is a large barrier as it prevents any implementation.<ref name="IHDP"/> The issues that arise with a system which involves international government cooperation, such as [[emissions trading|cap and trade]], could potentially be improved with a polycentric approach where the rules are enforced by many small sections of authority as opposed to one overall enforcement agency.<ref>{{cite web |url=http://www10.iadb.org/intal/intalcdi/pe/2009/04268.pdf |title=A Polycentric Approach for Coping with Climate Change |publisher=World Bank |date=October 2009 |author=Elinor Ostrom |archiveurl=https://web.archive.org/web/20131101164212/http://www10.iadb.org/intal/intalcdi/pe/2009/04268.pdf |archivedate=2013-11-01 |series=Policy Research Working Paper Series}}</ref> Concerns about metal requirement and/or availability for essential decarbonization technoloqies such as [[photovoltaics]], [[nuclear power]], and (plug-in hybrid) [[electric vehicle]]s have also been expressed as obstacles.<ref name="Tokimatsu">{{cite journal|last1=Tokimatsu|first1=Koji|last2=Wachtmeister|first2=Henrik|last3=McLellan|first3=Benjamin|last4=Davidsson|first4=Simon|last5=Murakami|first5=Shinsuke|last6=Höök|first6=Mikael|last7=Yasuoka|first7=Rieko|last8=Nishio|first8=Masahiro|title=Energy modeling approach to the global energy-mineral nexus: A first look at metal requirements and the 2 °C target|journal=Applied Energy|date=December 2017|volume=207|pages=494–509|doi=10.1016/j.apenergy.2017.05.151}}</ref>

====Occurrence====
Despite a perceived lack of occurrence, evidence of implementation is emerging internationally. Some examples of this are the initiation of NAPA's and of joint implementation. Many developing nations have made National Adaptation Programs of Action (NAPAs) which are frameworks to prioritize adaption needs.<ref name="EMJ">Preston. B. L, Westaway. R. M, Yuen. E. Y (2004) Climate adaptation planning in practice: an evaluation of adaptation plans from three developed nations, European Management Journal, 22(3) 304–314</ref> The implementation of many of these is supported by GEF agencies.<ref>UNFCCC (2011) Report on the twentieth meeting of the Least Developed Countries Expert Group, Subsidiary Body for Implementation, United Nations Framework Convention on Climate Change</ref> Many developed countries are implementing 'first generation' institutional adaption plans particularly at the state and local government scale.<ref name="EMJ"/> There has also been a push towards joint implementation between countries by the UNFCCC as this has been suggested as a cost-effective way for objectives to be achieved.<ref>UNFCCC (2011) Annual report of the Joint Implementation Supervisory Committee to the Conference of the Parties serving as the meeting of the Parties to the Kyoto Protocol, United Nations Framework Convention on Climate Change</ref>

===Territorial policies===
[[File:ETS and carbon tax world map.svg|thumb|350px|Carbon emission trading and carbon tax around the world<br/>
{{legend|#2ca25f|Emission trading implemented}}
{{legend|#addd8e|Emission trading scheduled}}
{{legend|#d95f0e|Carbon tax implemented}}
{{legend|#fec44f|Carbon tax scheduled}}
{{legend|#e8afe2|Emission trading or carbon tax under consideration}}]]
{{See also|List of countries by carbon dioxide emissions}}

====United States====
{{Main|Climate change in the United States}}
Efforts to reduce [[greenhouse gas emissions by the United States]] include [[energy policy of the United States|energy policies]] which encourage efficiency through programs like [[Energy Star]], [[Commercial Building Integration]], and the [[Industrial Technologies Program]].<ref>{{cite web|url=http://www.eere.energy.gov/industry/bestpractices/index.html |title=Industrial Technologies Program: BestPractices |publisher=Eere.energy.gov |accessdate=2010-08-26}}</ref> On 12 November 1998, Vice President [[Al Gore]] symbolically signed the Kyoto Protocol, but he indicated participation by the developing nations was necessary prior its being submitted for ratification by the [[United States Senate]].<ref>{{cite news|url=http://www.cnn.com/ALLPOLITICS/1997/12/11/kyoto/ |date=1997-12-11 |title=Clinton Hails Global Warming Pact|work= All Politics|publisher= CNN|accessdate=2006-11-05}}</ref>

In 2007, Transportation Secretary [[Mary Peters (politician)|Mary Peters]], with White House approval, urged governors and dozens of members of the House of Representatives to block California's first-in-the-nation limits on greenhouse gases from cars and trucks, according to e-mails obtained by Congress.<ref>[http://www.commondreams.org/archive/2007/09/25/4099/ "How the White House Worked to Scuttle California's Climate Law"], [[San Francisco Chronicle]], September 25, 2007</ref> The [[Climate Change Science Program|US Climate Change Science Program]] is a group of about twenty federal agencies and US Cabinet Departments, all working together to address global warming.

The [[Presidency of George W. Bush|Bush administration]] pressured American scientists to suppress discussion of global warming, according to the testimony of the Union of Concerned Scientists to the Oversight and Government Reform Committee of the US House of Representatives.<ref name=autogenerated2>Reuters, January 30, 2007, free archived version at http://www.commondreams.org/headlines07/0130-10.htm, last visited Jan. 30, '07</ref><ref>Written testimony of Dr. Grifo before the Committee on Oversight and Government Reform of the US House of Representatives on January 30, 2007, archived at {{cite web|url=http://oversight.house.gov/Documents/20070130113153-55829.pdf |title=Archived copy |accessdate=2009-12-15 |deadurl=yes |archiveurl=https://web.archive.org/web/20090805213620/http://oversight.house.gov/documents/20070130113153-55829.pdf |archivedate=2009-08-05 |df=}}</ref> "High-quality science" was "struggling to get out," as the Bush administration pressured scientists to tailor their writings on global warming to fit the Bush administration's skepticism, in some cases at the behest of an ex-oil industry lobbyist. "Nearly half of all respondents perceived or personally experienced pressure to eliminate the words 'climate change,' 'global warming' or other similar terms from a variety of communications." Similarly, according to the testimony of senior officers of the [[Government Accountability Project]], the White House attempted to bury the report "National Assessment of the Potential Consequences of Climate Variability and Change," produced by US scientists pursuant to US law.<ref>written testimony of Rick Piltz before the Committee on Oversight and Government Reform of the US House of Representatives on January 30, 2007, archived at {{cite web |url=http://oversight.house.gov/Documents/20070130113813-92288.pdf |title=Archived copy |accessdate=2007-01-31 |deadurl=yes |archiveurl=https://web.archive.org/web/20070131202854/http://oversight.house.gov/Documents/20070130113813-92288.pdf |archivedate=2007-01-31 |df=}} last visited Jan. 30, 07</ref> Some US scientists resigned their jobs rather than give in to White House pressure to underreport global warming.<ref name=autogenerated2/>

In the absence of substantial federal action, state governments have adopted emissions-control laws such as the [[Regional Greenhouse Gas Initiative]] in the Northeast and the [[Global Warming Solutions Act of 2006]] in California.<ref>{{cite news |url=https://www.nytimes.com/2012/10/14/science/earth/in-california-a-grand-experiment-to-rein-in-climate-change.html |work=The New York Times |first=Felicity |last=Barringer |title=In California, a Grand Experiment to Rein in Climate Change |date=2012-10-13}}</ref>

====Developing countries====
In order to reconcile [[economic development]] with mitigating carbon emissions, [[developing countries]] need particular support, both financial and technical. One of the means of achieving this is the Kyoto Protocol's [[Clean Development Mechanism]] (CDM). The [[World Bank]]'s Prototype Carbon Fund<ref>[http://carbonfinance.org/pcf/ Prototype Carbon Fund] from the World Bank Carbon Finance Unit</ref> is a [[public private partnership]] that operates within the CDM.

An important point of contention, however, is how overseas development assistance not directly related to climate change mitigation is affected by funds provided to climate change mitigation.<ref name=ODI>Jessica Brown, Neil Bird and Liane Schalatek (2010) [http://www.odi.org.uk/resources/details.asp?id=4931&title=climate-finance-additionality-definitions-implications Climate finance additionality: emerging definitions and their implications] [[Overseas Development Institute]]</ref> One of the outcomes of the UNFCC [[Copenhagen Climate Conference]] was the [[Copenhagen Accord]], in which developed countries promised to provide US$30&nbsp;million between 2010 and 2012 of new and additional resources.<ref name=ODI/> Yet it remains unclear what exactly the definition of additional is and the [[European Commission]] has requested its member states to define what they understand to be additional, and researchers at the [[Overseas Development Institute]] have found four main understandings:<ref name=ODI/>
# Climate finance classified as aid, but additional to (over and above) the [[Millennium Development Goals#Funding commitment|'0.7%' ODA target]];
# Increase on previous year's [[Official Development Assistance]] (ODA) spent on climate change mitigation;
# Rising ODA levels that include climate change finance but where it is limited to a specified percentage; and
# Increase in climate finance not connected to ODA.
The main point being that there is a conflict between the [[OECD]] states budget deficit cuts, the need to help developing countries adapt to develop sustainably and the need to ensure that funding does not come from cutting aid to other important [[Millennium Development Goals]].<ref name=ODI/>

However, none of these initiatives suggest a quantitative cap on the emissions from developing countries. This is considered as a particularly difficult policy proposal as the economic growth of developing countries are proportionally reflected in the growth of greenhouse emissions. Critics{{Who|date=May 2010}} of mitigation often argue that, the developing countries' drive to attain a comparable living standard to the developed countries would doom the attempt at mitigation of global warming. Critics{{Who|date=May 2010}} also argue that holding down emissions would shift the human cost of global warming from a general one to one that was borne most heavily by the poorest populations on the planet.

In an attempt to provide more opportunities for developing countries to adapt clean technologies, [[UNEP]] and [[WTO]] urged the international community to reduce trade barriers and to conclude the [[Doha Development Round|Doha trade round]] "which includes opening trade in environmental goods and services".<ref>[https://www.un.org/apps/news/story.asp?NewsID=31278&Cr=trade&Cr1=environment# Free trade can help combat global warming, finds UN report] UN News Centre, 26 June 2009</ref>

==Non-governmental approaches==
While many of the proposed methods of mitigating global warming require governmental funding, legislation and regulatory action, individuals and [[business action on climate change|businesses]] can also play a part in the mitigation effort.

===Choices in personal actions and business operations===
Environmental groups encourage [[individual and political action on climate change|individual action against global warming]], often aimed at the [[consumer]]. Common recommendations include lowering home heating and cooling usage, burning less gasoline, supporting renewable [[energy sources]], buying local products to reduce transportation, turning off unused devices, and various others.

A [[geophysicist]] at [[Utrecht University]] has urged similar institutions to hold the vanguard in voluntary mitigation, suggesting the use of communications technologies such as [[videoconferencing]] to reduce their dependence on long-haul flights.<ref>{{cite journal
|author=Andrew Biggin
|date=16 August 2007
|title=Scientific bodies must take own action on emissions
|journal=[[Nature (journal)|Nature]]
|volume=448
|issue=7155
|page=749
|doi=10.1038/448749a
|pmid=17700677
|bibcode= 2007Natur.448..749B}}</ref>

====Air travel and shipment====
In 2008, climate scientist [[Kevin Anderson (scientist)|Kevin Anderson]] raised concern about the growing effect of rapidly increasing global air transport on the climate in a paper,<ref>{{cite journal
|last=Anderson
|first=K
|last2=Bows
|first2=A
|year=2008
|url=http://rsta.royalsocietypublishing.org/content/366/1882/3863.full
|title= Reframing the climate change challenge in light of post-2000 emission trends
|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
|volume=366 |issue=1882 |pages=3863–82
|doi=10.1098/rsta.2008.0138|bibcode= 2008RSPTA.366.3863A}}</ref> and a presentation,<ref name="anderson">{{cite web
|last= Anderson
|first=K
|date=June 17, 2008
|url=http://transitionculture.org/wp-content/uploads/kevin-anderson-2.ppt
|title=Reframing climate change: from long-term targets to emission pathways
|quote= (esp. slide 24 onward)}}</ref> suggesting that reversing this trend is necessary to reduce emissions.

Part of the difficulty is that when [[environmental impact of aviation|aviation emissions]] are made at high altitude, the climate impacts are much greater than otherwise. Others have been raising the related concerns of the increasing [[hypermobility (travel)|hypermobility]] of individuals, whether traveling for business or pleasure, involving frequent and often long distance air travel, as well as air shipment of goods.<ref name="gossling">Gössling S, Ceron JP, Dubois G, Hall CM, Gössling IS, Upham P, [[Earthscan]] London (2009). Hypermobile travellers. and Implications for Carbon Dioxide Emissions Reduction. In: Climate Change and Aviation: Issues, Challenges and Solutions, London. The chapter: ''[https://alicante.academia.edu/documents/0076/1866/chap06_copy.pdf Chapter 6] {{webarchive|url=https://web.archive.org/web/20100619151427/http://alicante.academia.edu/documents/0076/1866/chap06_copy.pdf |date=2010-06-19}}''</ref>

===Business opportunities and risks===
{{Main|Business action on climate change}}

On 9 May 2005 [[Jeff Immelt]], the [[chief executive]] of [[General Electric]] (GE), announced plans to reduce GE's global warming related emissions by one percent by 2012. "GE said that given its projected growth, those emissions would have risen by 40 percent without such action."<ref>{{cite web |url=http://www.msnbc.msn.com/id/7791657/ |title=Green Electric? GE unveils eco-strategy |publisher=MSNBC}}</ref>

On 21 June 2005 a group of leading [[airline]]s, [[airport]]s, and [[aerospace]] [[manufacturer]]s pledged to work together to reduce the negative [[environmental impact of aviation]], including limiting the impact of air travel on climate change by improving [[fuel efficiency]] and reducing carbon dioxide emissions of new aircraft by fifty percent per seat kilometre by 2020 from 2000 levels. The group aims to develop a common reporting system for carbon dioxide emissions per aircraft by the end of 2005, and pressed for the early inclusion of aviation in the [[European Union]]'s carbon emission trading scheme.<ref>{{cite web |url=http://news.ft.com/cms/s/747d20ea-e1ff-11d9-bf18-00000e2511c8.html |title=Aviation groups set targets to limit their environmental impact |publisher=FT.com}}</ref>

===Investor response===
{{Main|Fossil fuel divestment}}
Climate change is also a concern for large institutional investors who have a long term time horizon and potentially large exposure to the negative impacts of global warming because of the large geographic footprint of their multi-national holdings. SRI ([[Socially responsible investing]]) Funds allow investors to invest in funds that meet high ESG (environmental, social, governance) standards as such funds invest in companies that are aligned with these goals.<ref>{{cite web |url=http://www.kiplinger.com/article/investing/T041-C016-S001-5-mutual-funds-for-socially-responsible-investors.html |title=5 Mutual Funds for Socially Responsible Investors |publisher=Kiplinger}}</ref> [[Proxy firm]]s can be used to draft guidelines for [[investment manager]]s that take these concerns into account.<ref>{{cite web |url=http://www.ussif.org/files/publications/institutional_climate.pdf |title=Investing to Curb Climate Change |publisher=USSIF |page=2}}</ref>

===Legal action===
{{See also|Duty to rescue}}

In some countries, those affected by climate change may be able to sue major producers. Attempts at litigation have been initiated by entire peoples such as Palau<ref>{{cite web|url=https://www.pbs.org/wnet/need-to-know/video/video-paradise-lost/14421/|title=Video: Paradise lost? – Need to Know |publisher=PBS|quote=Palau suing the industrialized countries over global warming}}</ref> and the Inuit,<ref>[http://www.msnbc.msn.com/id/6908719/site/newsweek/ Inuit suing the US in regards to global warming] {{webarchive |url=https://web.archive.org/web/20100825135526/http://www.msnbc.msn.com/id/6908719/site/newsweek/ |date=August 25, 2010}}</ref> as well as non-governmental organizations such as the Sierra Club.<ref>{{cite web|url=http://www.newson6.com/story/9138384/environmental-integrity-project-sierra-club-announce-plans-to-sue-epa-unless-it-revises-nitrogen-oxide-emissions-standard-curbs-nitrous-oxide?clienttype=printable|title=Environmental Integrity Project, Sierra Club Announce Plans to Sue EPA Unless It Revises Nitrogen Oxide Emissions Standard, Curbs Nitrous Oxide Pollution Linked to Global Warming – NewsOn6.com – Tulsa, OK – News, Weather, Video and Sports – KOTV.com -|publisher=}}</ref> Although proving that particular weather events are due specifically to global warming may never be possible,<ref>Edward Lorenz (1982): "Climate is what you expect, weather is what you get"</ref> methodologies have been developed to show the increased risk of such events caused by global warming.<ref>Stott, et al. (2004), "Human contribution to the European heatwave of 2003", Nature, Vol. 432, 2 December 2004</ref>

For a legal action for [[negligence]] (or similar) to succeed, "Plaintiffs ... must show that, more probably than not, their individual injuries were caused by the risk factor in question, as opposed to any other cause. This has sometimes been translated to a requirement of a relative risk of at least two."<ref>Grossman, Columbia J. of Env. Law, 2003</ref> Another route (though with little legal bite) is the [[World Heritage Convention]], if it can be shown that climate change is affecting [[World Heritage Site]]s like [[Mount Everest]].<ref>{{cite web|url=http://www.heatisonline.org/contentserver/objecthandlers/index.cfm?id=4950&method=full |title=Climate change 'ruining' Everest |publisher=Heatisonline.org |date=2004-11-17 |access-date=2010-08-26}}</ref><ref>[http://www.bbc.co.uk/caribbean/news/story/2004/11/041117_climate-belize.shtml Climate change 'ruining' Belize] BBC November 2004</ref>

Besides countries suing one another, there are also cases where people in a country have taken legal steps against their own government. Legal action for instance has been taken to try to force the [[United States Environmental Protection Agency|US Environmental Protection Agency]] to regulate greenhouse gas emissions under the [[Clean Air Act (United States)|Clean Air Act]],<ref>[http://www.climatelaw.org/cases Climate Justice] Ongoing Cases</ref> and against the [[Export-Import Bank of the United States|Export-Import Bank]] and [[Overseas Private Investment Corporation|OPIC]] for failing to assess environmental impacts (including global warming impacts) under [[NEPA]].{{Citation needed|date=September 2007}}

In the Netherlands and Belgium, organisations such as [[Urgenda]]<ref>{{cite web|url=https://www.theguardian.com/environment/2015/jun/24/dutch-government-ordered-cut-carbon-emissions-landmark-ruling|title=Dutch government ordered to cut carbon emissions in landmark ruling|first=Arthur Neslen The|last=Hague|date=24 June 2015|publisher=The Guardian}}</ref><ref>{{cite web|url=http://www.urgenda.nl/themas/klimaat-en-energie/klimaatzaak/|title=Klimaat en Energie – Thema's – Urgenda – Samen Sneller Duurzaam|publisher=}}</ref><ref>{{cite web|url=http://tegenlicht.vpro.nl/afleveringen/2015-2016/de-klimaatzaak.html|title=VPRO Tegenlicht|publisher=}}</ref> and the [[vzw Klimaatzaak]] in Belgium<ref>{{cite web|url=http://deredactie.be/cm/vrtnieuws/binnenland/2.36678|title=Klimaatzaak|publisher=}}</ref><ref>{{cite web|url=http://klimaatzaak.eu/nl/about/|title=Over ons – Klimaatzaak|publisher=}}</ref> have also sued their governments as they believe their governments aren't meeting the emission reductions they agreed to. Urgenda have already won their case against the Dutch government.{{citation needed|date=July 2017}}

According to a 2004 study commissioned by [[Friends of the Earth]], [[ExxonMobil]], and its predecessors caused 4.7 to 5.3 percent of the world's man-made carbon dioxide emissions between 1882 and 2002. The group suggested that such studies could form the basis for eventual legal action.<ref>Press release (29 January 2004). [http://www.foe.co.uk/resource/press_releases/exxonmobils_contribution_t_28012004.html Archived press release: Exxonmobil's contribution to global warming revealed]. Friends of the Earth Trust. Retrieved May 25, 2015.</ref>

In 2015, [[Exxon]] received a subpoena. According to the ''Washington Post'' and confirmed by the company, the attorney general of New York, [[Eric Schneiderman]], opened an investigation into the possibility that the company had misled the public and investors about the risks of climate change.<ref>{{cite web|url=https://www.washingtonpost.com/news/energy-environment/wp/2015/11/05/exxonmobil-under-investigation-for-misleading-the-public-about-climate-change/ |title=New York is investigating Exxon Mobil for allegedly misleading the public about climate change |publisher=The Washington Post |date=November 5, 2015 |access-date=December 29, 2015}}</ref>


== Tham khảo ==
== Tham khảo ==

Phiên bản lúc 04:20, ngày 17 tháng 5 năm 2018

Phát thải CO2 liên quan đến nhiên liệu hóa thạch so với năm kịch bản phát thải của IPCC. Sự suy giảm liên quan đến suy thoái kinh tế toàn cầu. Dữ liệu từ IPCC SRES scenarios; Data spreadsheet included with International Energy Agency's "CO2 Emissions from Fuel Combustion 2010 – Highlights"; và Dữ liệu bổ sung của IEA. Nguồn ảnh: Skeptical Science.
Nhiệt độ bề mặt trung bình toàn cầu thay đổi từ 1880 đến 2016, so với trung bình năm 1951-1980. Đường màu đen là trung bình toàn cầu hàng năm và đường màu đỏ là số liệu năm năm hồi quy cục bộ. Giá trị không chắc chắn màu xanh hiển thị giới hạn độ tin cậy 95%. Nguồn: NASA GISS. Global dimming, từ ô nhiễm không khí sulfat, từ năm 1950 đến năm 1980 được cho là đã làm giảm hiện tượng ấm lên toàn cầu.
Khí thải carbon dioxide toàn cầu từ các hoạt động của con người, 1800–2007.[1]
Khí nhà kính thải ra tính theo lĩnh vực. Xem World Resources Institute để có thông tin chi tiết hơn.
refer to caption and image description
Global public support for energy sources, based on a survey by Ipsos (2011).[2] Ipsos (2012)[3]

Giảm thiểu biến đổi khí hậu là các hành động để hạn chế cường độ hoặc tỷ lệ dài hạn biến đổi khí hậu.[4] Giảm nhẹ biến đổi khí hậu nói chung liên quan đến việc cắt giảm lượng phát thải khí nhà kính của con người.[5] Giảm nhẹ cũng có thể đạt được bằng cách tăng khả năng chứa đựng các-bon, ví dụ, thông qua trồng rừng. Các chính sách giảm thiểu có thể làm giảm đáng kể các rủi ro liên quan đến sự nóng lên toàn cầu do con người gây ra.[6]

Theo báo cáo đánh giá năm 2014 của IPCC "Việc giảm thiểu là một lợi ích công cộng; thay đổi khí hậu là một trường hợp 'cha chung không ai khóc'. Giảm thiểu tác động của biến đổi khí hậu một cách hiệu quả sẽ không đạt được nếu mỗi đối tượng (cá nhân, tổ chức hoặc quốc gia) hoạt động độc lập theo lợi ích ích kỷ của chính mình (xem hợp tác quốc tế và mua bán thải carbon), cho thấy phải có hành động tập thể. Mặt khác, một số hành động thích ứng có đặc điểm của một lợi ích cá nhân vì lợi ích của các hành động có thể mang tính tích luỹ trực tiếp hơn cho các cá nhân, khu vực, hoặc các quốc gia thực hiện nó, ít nhất là trong thời gian ngắn hạn. Tuy nhiên, việc tài trợ cho các hoạt động thích ứng vẫn là một vấn đề, đặc biệt đối với các cá nhân và các nước nghèo."[7]

Greenhouse gas concentrations and stabilization

refer to caption and adjacent text
Stabilizing CO2 emissions at their present level would not stabilize its concentration in the atmosphere.[8]
refer to caption and adjacent text
Stabilizing the atmospheric concentration of CO2 at a constant level would require emissions to be effectively eliminated.[8]

One of the issues often discussed in relation to climate change mitigation is the stabilization of greenhouse gas concentrations in the atmosphere. The United Nations Framework Convention on Climate Change (UNFCCC) has the ultimate objective of preventing "dangerous" anthropogenic (i.e., human) interference of the climate system. As is stated in Article 2 of the Convention, this requires that greenhouse gas (GHG) concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can proceed in a sustainable fashion.[9]

There are a number of anthropogenic greenhouse gases. These include carbon dioxide (chemical formula: CO2), methane (CH
4
), nitrous oxide (N
2
O
), and a group of gases referred to as halocarbons.[10] The emissions reductions necessary to stabilize the atmospheric concentrations of these gases varies.[8] CO2 is the most important of the anthropogenic greenhouse gases (see radiative forcing).[11]

There is a difference between stabilizing CO2 emissions and stabilizing atmospheric concentrations of CO2.[12] Stabilizing emissions of CO2 at current levels would not lead to a stabilization in the atmospheric concentration of CO2. In fact, stabilizing emissions at current levels would result in the atmospheric concentration of CO2 continuing to rise over the 21st century and beyond (see the graphs opposite).

The reason for this is that human activities are adding CO2 to the atmosphere faster than natural processes can remove it (see carbon dioxide in Earth's atmosphere for a complete explanation).[8] This is analogous to a flow of water into a bathtub.[13] So long as the tap runs water (analogous to the emission of carbon dioxide) into the tub faster than water escapes through the plughole (the natural removal of carbon dioxide from the atmosphere), then the level of water in the tub (analogous to the concentration of carbon dioxide in the atmosphere) will continue to rise.

According to some studies, stabilizing atmospheric CO2 concentrations would require anthropogenic CO2 emissions to be reduced by 80% relative to the peak emissions level.[14] An 80% reduction in emissions would stabilize CO2 concentrations for around a century, but even greater reductions would be required beyond this.[8][14] Other research has found that, after leaving room for emissions for food production for 9 billion people and to keep the global temperature rise below 2 °C, emissions from energy production and transport will have to peak almost immediately in the developed world and decline at ca. 10% per annum until zero emissions are reached around 2030. In developing countries energy and transport emissions would have to peak by 2025 and then decline similarly.[15][16][17][18]

Stabilizing the atmospheric concentration of the other greenhouse gasses humans emit also depends on how fast their emissions are added to the atmosphere, and how fast the GHGs are removed. Stabilization for these gases is described in the later section on non-CO2 GHGs.

Projections

Projections of future greenhouse gas emissions are highly uncertain.[19] In the absence of policies to mitigate climate change, GHG emissions could rise significantly over the 21st century.[20]

Numerous assessments have considered how atmospheric GHG concentrations could be stabilized.[21] The lower the desired stabilization level, the sooner global GHG emissions must peak and decline.[22] GHG concentrations are unlikely to stabilize this century without major policy changes.[20]

refer to caption and adjacent text
Projected carbon dioxide emissions and atmospheric concentrations over the 21st century for reference and mitigation scenarios
Rate of world energy usage per day, from 1970 to 2010. Every fossil fuel source has increased in large amounts between 1970 and 2010, dominating all other energy sources. Hydroelectricity has increased at a slow steady rate over this same period, nuclear entered a period of rapid growth between 1970 and 1990 before leveling off. Other renewables, between 2000 and 2010 have, having started from a low usage rate, began to enter into a period of rapid growth. 1000 TWh=1 PWh.[23]

Energy consumption by power source

"Hydropower-Internalised Costs and Externalised Benefits"; Frans H. Koch; International Energy Agency (IEA)-Implementing Agreement for Hydropower Technologies and Programmes; 2000.

To create lasting climate change mitigation, the replacement of high carbon emission intensity power sources, such as conventional fossil fuelsoil, coal, and natural gas—with low-carbon power sources is required. Fossil fuels supply humanity with the vast majority of our energy demands, and at a growing rate. In 2012 the IEA noted that coal accounted for half the increased energy use of the prior decade, growing faster than all renewable energy sources.[24] Both hydroelectricity and nuclear power together provide the majority of the generated low-carbon power fraction of global total power consumption.

Fuel type Average total global power consumption in TW[25]
1980 2004 2006
Oil 4.38 5.58 5.74
Gas 1.80 3.45 3.61
Coal 2.34 3.87 4.27
Hydroelectric 0.60 0.93 1.00
Nuclear power 0.25 0.91 0.93
Geothermal, wind,
solar energy, wood
0.02 0.13 0.16
Total 9.48 15.0 15.8
Source: The USA Energy Information Administration
Change and use of energy, by source, in units of (PWh) in that year.[26]
Fossil Nuclear All renewables Total
1990 83.374 6.113 13.082 102.569
2000 94.493 7.857 15.337 117.687
2008 117.076 8.283 18.492 143.851
Change 2000–2008 22.583 0.426 3.155 26.164

Methods and means

Refer to caption and image description
This graph shows the projected contribution of various energy sources to world primary electricity consumption (PEC).[27] It is based on a climate change mitigation scenario, in which GHG emissions are substantially reduced over the 21st century. In the scenario, emission reductions are achieved using a portfolio of energy sources, as well as reductions in energy demand. Also available in greyscale.

Assessments often suggest that GHG emissions can be reduced using a portfolio of low-carbon technologies.[28] At the core of most proposals is the reduction of greenhouse gas (GHG) emissions through reducing energy waste and switching to low-carbon power sources of energy. As the cost of reducing GHG emissions in the electricity sector appears to be lower than in other sectors, such as in the transportation sector, the electricity sector may deliver the largest proportional carbon reductions under an economically efficient climate policy.[29]

"Economic tools can be useful in designing climate change mitigation policies." "While the limitations of economics and social welfare analysis, including cost–benefit analysis, are widely documented, economics nevertheless provides useful tools for assessing the pros and cons of taking, or not taking, action on climate change mitigation, as well as of adaptation measures, in achieving competing societal goals. Understanding these pros and cons can help in making policy decisions on climate change mitigation and can influence the actions taken by countries, institutions and individuals."[7]

Other frequently discussed means include energy conservation, increasing fuel economy in automobiles (which includes the use of electric hybrids), charging plug-in hybrids and electric cars by low-carbon electricity, making individual-lifestyle changes[30] (e.g., cycling instead of driving),[31] and changing business practices. Many fossil fuel driven vehicles can be converted to use electricity, the US has the potential to supply electricity for 73% of light duty vehicles (LDV), using overnight charging. The US average CO2 emissions for a battery-electric car is 180 grams per mile vs 430 grams per mile for a gasoline car.[32] The emissions would be displaced away from street level, where they have "high human-health implications. Increased use of electricity "generation for meeting the future transportation load is primarily fossil-fuel based", mostly natural gas, followed by coal,[33] but could also be met through nuclear, tidal, hydroelectric and other sources.

A range of energy technologies may contribute to climate change mitigation.[34] These include nuclear power and renewable energy sources such as biomass, hydroelectricity, wind power, solar power, geothermal power, ocean energy, and; the use of carbon sinks, and carbon capture and storage. For example, Pacala and Socolow of Princeton[35] have proposed a 15 part program to reduce CO2 emissions by 1 billion metric tons per year − or 25 billion tons over the 50-year period using today's technologies as a type of global warming game.[36]

Another consideration is how future socioeconomic development proceeds. Development choices (or "pathways") can lead differences in GHG emissions.[37] Political and social attitudes may affect how easy or difficult it is to implement effective policies to reduce emissions.[38]

Demand side management

Lifestyle and behavior

The IPCC Fifth Assessment Report emphasises that behaviour, lifestyle, and cultural change have a high mitigation potential in some sectors, particularly when complementing technological and structural change.[39]:20 In general, higher consumption lifestyles have a greater environmental impact. Several scientific studies have shown that when people, especially those living in developed countries but more generally including all countries, wish to reduce their carbon footprint, there are four key "high-impact" actions they can take:[40][41][42]

1. Not having an additional child (58.6 tonnes CO2-equivalent emission reductions per year)
2. Living car-free (2.4 tonnes CO2)
3. Avoiding one round-trip transatlantic flight (1.6 tonnes)
4. Eating a plant-based diet (0.8 tonnes)

These appear to differ significantly from the popular advice for “greening” one's lifestyle, which seem to fall mostly into the “low-impact” category: Replacing a typical car with a hybrid (0.52 tonnes); Washing clothes in cold water (0.25 tonnes); Recycling (0.21 tonnes); Upgrading light bulbs (0.10 tonnes); etc. The researchers found that public discourse on reducing one's carbon footprint overwhelmingly focuses on low-impact behaviors, and that mention of the high-impact behaviors is almost non-existent in the mainstream media, government publications, K-12 school textbooks, etc.[40][41][42]

The researchers added that “Our recommended high-impact actions are more effective than many more commonly discussed options (e.g. eating a plant-based diet saves eight times more emissions than upgrading light bulbs). More significantly, a US family who chooses to have one fewer child would provide the same level of emissions reductions as 684 teenagers who choose to adopt comprehensive recycling for the rest of their lives.”[40][41][42]

Dietary change

Overall, food accounts for the largest share of consumption-based GHG emissions with nearly 20% of the global carbon footprint, followed by housing, mobility, services, manufactured products, and construction. Food and services are more significant in poor countries, while mobility and manufactured goods are more significant in rich countries.[43]:327 A 2014 study into the real-life diets of British people estimates their greenhouse gas contributions (CO2eq) to be: 7.19 kg/day for high meat-eaters through to 3.81 kg/day for vegetarians and 2.89 kg/day for vegans.[44] The widespread adoption of a vegetarian diet could cut food-related greenhouse gas emissions by 63% by 2050.[45] China introduced new dietary guidelines in 2016 which aim to cut meat consumption by 50% and thereby reduce greenhouse gas emissions by 1 billion tonnes by 2030.[46] A 2016 study concluded that taxes on meat and milk could simultaneously result in reduced greenhouse gas emissions and healthier diets. The study analyzed surcharges of 40% on beef and 20% on milk and suggests that an optimum plan would reduce emissions by 1 billion tonnes per year.[47][48]

Energy efficiency and conservation

A 230-volt LED light bulb, with an E27 base (10 watts, 806 lumens).

Efficient energy use, sometimes simply called "energy efficiency", is the goal of efforts to reduce the amount of energy required to provide products and services. For example, insulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature. Installing LED lighting, fluorescent lighting, or natural skylight windows reduces the amount of energy required to attain the same level of illumination compared to using traditional incandescent light bulbs. Compact fluorescent lamps use only 33% of the energy and may last 6 to 10 times longer than incandescent lights.[49] LED lamps use only about 10% of the energy an incandescent lamp requires.

Energy efficiency has proved to be a cost-effective strategy for building economies without necessarily growing energy consumption. For example, the state of California began implementing energy-efficiency measures in the mid-1970s, including building code and appliance standards with strict efficiency requirements. During the following years, California's energy consumption has remained approximately flat on a per capita basis while national US consumption doubled. As part of its strategy, California implemented a "loading order" for new energy resources that puts energy efficiency first, renewable electricity supplies second, and new fossil-fired power plants last.[50]

Energy conservation is broader than energy efficiency in that it encompasses using less energy to achieve a lesser energy demanding service, for example through behavioral change, as well as encompassing energy efficiency. Examples of conservation without efficiency improvements would be heating a room less in winter, driving less, or working in a less brightly lit room. As with other definitions, the boundary between efficient energy use and energy conservation can be fuzzy, but both are important in environmental and economic terms. This is especially the case when actions are directed at the saving of fossil fuels.[51]

Reducing energy use is seen as a key solution to the problem of reducing greenhouse gas emissions. According to the International Energy Agency, improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.[52]

Demand-side switching sources

Fuel switching on the demand side refers to changing the type of fuel used to satisfy a need for an energy service. To meet deep decarbonization goals, like the 80% reduction by 2050 goal being discussed in California and the European Union, many primary energy changes are needed.[53][54] Energy efficiency alone may not be sufficient to meet these goals, switching fuels used on the demand side will help lower carbon emissions.[55][56] Progressively coal, oil and eventually natural gas for space and water heating in buildings will need to be reduced. For an equivalent amount of heat, burning natural gas produces about 45 per cent less carbon dioxide than burning coal.[57] There are various ways in which this could happen, and different strategies will likely make sense in different locations. While the system efficiency of a gas furnace may be higher than the combination of natural gas power plant and electric heat, the combination of the same natural gas power plant and an electric heat pump has lower emissions per unit of heat delivered in all but the coldest climates. This is possible because of the very efficient coefficient of performance of heat pumps.

At the beginning of this century 70% of all electricity was generated by fossil fuels, and as carbon free sources eventually make up half of the generation mix, replacing gas or oil furnaces and water heaters with electric ones will have a climate benefit. In areas like Norway, Brazil, and Quebec that have abundant hydroelectricity, electric heat and hot water are common.

The economics of switching the demand side from fossil fuels to electricity for heating, will depend on the price of fuels vs electricity and the relative prices of the equipment. The EIA Annual Energy Outlook 2014 suggests that domestic gas prices will rise faster than electricity prices which will encourage electrification in the coming decades.[58] Electrifying heating loads may also provide a flexible resource that can participate in demand response. Since thermostatically controlled loads have inherent energy storage, electrification of heating could provide a valuable resource to integrate variable renewable resources into the grid.

Alternatives to electrification, include decarbonizing pipeline gas through power to gas, biogas, or other carbon-neutral fuels. A 2015 study by Energy+Environmental Economics shows that a hybrid approach of decarbonizing pipeline gas, electrification, and energy efficiency can meet carbon reduction goals at a similar cost as only electrification and energy efficiency in Southern California.[59]

Demand side grid management

Expanding intermittent electrical sources such as wind power, creates a growing problem balancing grid fluctuations. Some of the plans include building pumped storage or continental super grids costing billions of dollars. However instead of building for more power, there are a variety of ways to affect the size and timing of electricity demand on the consumer side. Designing for reduced demands on a smaller power grid is more efficient and economic than having extra generation and transmission for intermittentcy, power failures and peak demands. Having these abilities is one of the chief aims of a smart grid.

Time of use metering is a common way to motivate electricity users to reduce their peak load consumption. For instance, running dishwashers and laundry at night after the peak has passed, reduces electricity costs.

Dynamic demand plans have devices passively shut off when stress is sensed on the electrical grid. This method may work very well with thermostats, when power on the grid sags a small amount, a low power temperature setting is automatically selected reducing the load on the grid. For instance millions of refrigerators reduce their consumption when clouds pass over solar installations. Consumers would need to have a smart meter in order for the utility to calculate credits.

Demand response devices could receive all sorts of messages from the grid. The message could be a request to use a low power mode similar to dynamic demand, to shut off entirely during a sudden failure on the grid, or notifications about the current and expected prices for power. This would allow electric cars to recharge at the least expensive rates independent of the time of day. The vehicle-to-grid suggestion would use a car's battery or fuel cell to supply the grid temporarily.

Alternative energy sources

Renewable energy

The worldwide growth of renewable energy is shown by the green line[60]
The 22,500 MW nameplate capacity Three Gorges Dam in the Peoples Republic of China, the largest hydroelectric power station in the world.
The Shepherds Flat Wind Farm is an 845 megawatt (MW) nameplate capacity, wind farm in the US state of Oregon, each turbine is a nameplate 2 or 2.5 MW electricity generator.
The 150 MW Andasol solar power station is a commercial parabolic trough solar thermal power plant, located in Spain. The Andasol plant uses tanks of molten salt to store solar energy so that it can continue generating electricity for 7.5 hours after the sun has stopped shining.[61]
Solar cookers use sunlight as energy source for outdoor cooking.

Renewable energy flows involve natural phenomena such as sunlight, wind, rain, tides, plant growth, and geothermal heat, as the International Energy Agency explains:[62]

Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources.

Climate change concerns[63][64][65] and the need to reduce carbon emissions are driving increasing growth in the renewable energy industries.[66][67][68] Low-carbon renewable energy replaces conventional fossil fuels in three main areas: power generation, hot water/ space heating, and transport fuels.[69] In 2011, the share of renewables in electricity generation worldwide grew for the fourth year in a row to 20.2%.[70] Based on REN21's 2014 report, renewables contributed 19% to supply global energy consumption. This energy consumption is divided as 9% coming from burning biomass, 4.2% as heat energy (non-biomass), 3.8% hydro electricity and 2% as electricity from wind, solar, geothermal, and biomass thermal power plants.[71]

Renewable energy use has grown much faster than anyone anticipated.[72] The Intergovernmental Panel on Climate Change (IPCC) has said that there are few fundamental technological limits to integrating a portfolio of renewable energy technologies to meet most of total global energy demand.[73] At the national level, at least 30 nations around the world already have renewable energy contributing more than 20% of energy supply.

As of 2012, renewable energy accounts for almost half of new electricity capacity installed and costs are continuing to fall.[74] Public policy and political leadership helps to "level the playing field" and drive the wider acceptance of renewable energy technologies.[75] Tính đến năm 2011, 118 countries have targets for their own renewable energy futures, and have enacted wide-ranging public policies to promote renewables.[76][77] Leading renewable energy companies include BrightSource Energy, First Solar, Gamesa, GE Energy, Goldwind, Sinovel, Suntech, Trina Solar, Vestas, and Yingli.[78][79]

The incentive to use 100% renewable energy has been created by global warming and other ecological as well as economic concerns.[72] Mark Z. Jacobson says producing all new energy with wind power, solar power, and hydropower by 2030 is feasible and existing energy supply arrangements could be replaced by 2050. Barriers to implementing the renewable energy plan are seen to be "primarily social and political, not technological or economic". Jacobson says that energy costs with a wind, solar, water system should be similar to today's energy costs.[80] According to a 2011 projection by the (IEA)International Energy Agency, solar power generators may produce most of the world's electricity within 50 years, dramatically reducing harmful greenhouse gas emissions.[81] Critics of the "100% renewable energy" approach include Vaclav Smil and James E. Hansen. Smil and Hansen are concerned about the variable output of solar and wind power, NIMBYism, and a lack of infrastructure.[82]

Economic analysts expect market gains for renewable energy (and efficient energy use) following the 2011 Japanese nuclear accidents.[83][84] In his 2012 State of the Union address, President Barack Obama restated his commitment to renewable energy and mentioned the long-standing Interior Department commitment to permit 10,000 MW of renewable energy projects on public land in 2012.[85] Globally, there are an estimated 3 million direct jobs in renewable energy industries, with about half of them in the biofuels industry.[86]

Some countries, with favorable geography, geology, and weather well suited to an economical exploitation of renewable energy sources, already get most of their electricity from renewables, including from geothermal energy in Iceland (100 percent), and hydroelectric power in Brazil (85 percent), Austria (62 percent), New Zealand (65 percent), and Sweden (54 percent).[87] Renewable power generators are spread across many countries, with wind power providing a significant share of electricity in some regional areas: for example, 14 percent in the US state of Iowa, 40 percent in the northern German state of Schleswig-Holstein, and 20 percent in Denmark. Solar water heating makes an important and growing contribution in many countries, most notably in China, which now has 70 percent of the global total (180 GWth). Worldwide, total installed solar water heating systems meet a portion of the water heating needs of over 70 million households. The use of biomass for heating continues to grow as well. In Sweden, national use of biomass energy has surpassed that of oil. Direct geothermal heating is also growing rapidly.[87] Renewable biofuels for transportation, such as ethanol fuel and biodiesel, have contributed to a significant decline in oil consumption in the United States since 2006. The 93 billion liters of biofuels produced worldwide in 2009 displaced the equivalent of an estimated 68 billion liters of gasoline, equal to about 5 percent of world gasoline production.[87]

Some of the world's largest solar power stations: Ivanpah (CSP) and Topaz (PV), both in California

Nuclear power

Blue Cherenkov light being produced near the core of the Fission powered Advanced Test Reactor

Since about 2001 the term "nuclear renaissance" has been used to refer to a possible nuclear power industry revival, driven by rising fossil fuel prices and new concerns about meeting greenhouse gas emission limits.[88] However, in March 2011 the Fukushima nuclear disaster in Japan and associated shutdowns at other nuclear facilities raised questions among some commentators over the future of nuclear power.[89][90][91] Platts has reported that "the crisis at Japan's Fukushima nuclear plants has prompted leading energy-consuming countries to review the safety of their existing reactors and cast doubt on the speed and scale of planned expansions around the world".[92]

The World Nuclear Association has reported that nuclear electricity generation in 2012 was at its lowest level since 1999.[93] Several previous international studies and assessments,[94][95][96] suggested that as part of the portfolio of other low-carbon energy technologies, nuclear power will continue to play a role in reducing greenhouse gas emissions. Historically, nuclear power usage is estimated to have prevented the atmospheric emission of 64 gigatonnes of CO2-equivalent as of 2013.[97] Public concerns about nuclear power include the fate of spent nuclear fuel, nuclear accidents, security risks, nuclear proliferation, and a concern that nuclear power plants are very expensive.[98][99][100] Of these concerns, nuclear accidents and disposal of long-lived radioactive fuel/"waste" have probably had the greatest public impact worldwide.[98] Although generally unaware of it, both of these glaring public concerns are greatly diminished by present passive safety designs, the experimentally proven, "melt-down proof" EBR-II, future molten salt reactors, and the use of conventional and more advanced fuel/"waste" pyroprocessing,[101] with the latter recycling or reprocessing not presently being commonplace as it is often considered to be cheaper to use a once-through nuclear fuel cycle in many countries, depending on the varying levels of intrinsic value given by a society in reducing the long-lived waste in their country, with France doing a considerable amount of reprocessing when compared to the US.[102][103]

Nuclear power, with a 10.6% share of world electricity production as of 2013, is second only to hydroelectricity as the largest source of low-carbon power.[104] Over 400 reactors generate electricity in 31 countries.[105]

A Yale University review published in the Journal of Industrial Ecology analyzing CO2 life cycle assessment(LCA) emissions from nuclear power(light water reactors) determined that: "The collective LCA literature indicates that life cycle GHG emissions from nuclear power are only a fraction of traditional fossil sources and comparable to renewable technologies."[106] While some have raised uncertainty surrounding the future GHG emissions of nuclear power as a result of an extreme potential decline in uranium ore grade without a corresponding increase in the efficiency of enrichment methods. In a scenario analysis of future global nuclear development, as it could be effected by a decreasing global uranium market of average ore grade, the analysis determined that depending on conditions, median life cycle nuclear power GHG emissions could be between 9 and 110 g CO2-eq/kWh by 2050, with the latter high figure being derived from a "worst-case scenario" that is not "considered very robust" by the authors of the paper, as the "ore grade" in the scenario is lower than the uranium concentration in many lignite coal ashes.[106]

Although this future analyses primarily deals with extrapolations for present Generation II reactor technology, the same paper also summarizes the literature on "FBRs"/Fast Breeder Reactors, of which two are in operation as of 2014 with the newest being the BN-800, for these reactors it states that the "median life cycle GHG emissions ... [are] similar to or lower than [present light water reactors] LWRs and purports to consume little or no uranium ore.[106]

In their 2014 report, the IPCC comparison of energy sources global warming potential per unit of electricity generated, which notably included albedo effects, mirror the median emission value derived from the Warner and Heath Yale meta-analysis for the more common non-breeding light water reactors, a CO2-equivalent value of 12 g CO2-eq/kWh, which is the lowest global warming forcing of all baseload power sources, with comparable low carbon power baseload sources, such as hydropower and biomass, producing substantially more global warming forcing 24 and 230 g CO2-eq/kWh respectively.[107]

In 2014, Brookings Institution published The Net Benefits of Low and No-Carbon Electricity Technologies which states, after performing an energy and emissions cost analysis, that "The net benefits of new nuclear, hydro, and natural gas combined cycle plants far outweigh the net benefits of new wind or solar plants", with the most cost effective low carbon power technology being determined to be nuclear power.[108][109][110]

During his presidential campaign, Barack Obama stated, "Nuclear power represents more than 70% of our noncarbon generated electricity. It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power as an option."[111]

This graph illustrates nuclear power is the United States's largest contributor of non-greenhouse-gas-emitting electric power generation, comprising nearly three-quarters of the non-emitting sources.

Analysis in 2015 by Professor and Chair of Environmental Sustainability Barry W. Brook and his colleagues on the topic of replacing fossil fuels entirely, from the electric grid of the world, has determined that at the historically modest and proven-rate at which nuclear energy was added to and replaced fossil fuels in France and Sweden during each nation's building programs in the 1980s, within 10 years nuclear energy could displace or remove fossil fuels from the electric grid completely, "allow[ing] the world to meet the most stringent greenhouse-gas mitigation targets.".[112] In a similar analysis, Brook had earlier determined that 50% of all global energy, that is not solely electricity, but transportation synfuels etc. could be generated within approximately 30 years, if the global nuclear fission build rate was identical to each of these nation's already proven decadal rates(in units of installed nameplate capacity, GW per year, per unit of global GDP(GW/year/$).[113][114][115]

This is in contrast to the completely conceptual paper-studies for a 100% renewable energy world, which would require an orders of magnitude more costly global investment per year, an investment rate that has no historical precedent, having never been attempted due to its prohibitive cost,[114][116] and with far greater land area that would be required to be devoted to the wind, wave and solar projects, along with the inherent assumption that humanity will use less, and not more, energy in the future.[113][114][115] As Brook notes the "principal limitations on nuclear fission are not technical, economic or fuel-related, but are instead linked to complex issues of societal acceptance, fiscal and political inertia, and inadequate critical evaluation of the real-world constraints facing [the other] low-carbon alternatives."[113]

Nuclear power may be uncompetitive compared with fossil fuel energy sources in countries without a carbon tax program, and in comparison to a fossil fuel plant of the same power output, nuclear power plants take a longer amount of time to construct.[117][118][119][120]

Two new, first of their kind, EPR reactors under construction in Finland and France have been delayed and are running over-budget.[121][122][123] However learning from experience, two further EPR reactors under construction in China are on, and ahead, of schedule respectively.[124] As of 2013, according to the IAEA and the European Nuclear Society, worldwide there were 68 civil nuclear power reactors under construction in 15 countries.[125][126] China has 29 of these nuclear power reactors under construction, as of 2013, with plans to build many more,[126][127] while in the US the licenses of almost half its reactors have been extended to 60 years,[128] and plans to build another dozen are under serious consideration.[129] There are also a considerable number of new reactors being built in South Korea, India, and Russia. At least 100 older and smaller reactors will "most probably be closed over the next 10–15 years".[130] This is probable only if one does not factor in the ongoing Light Water Reactor Sustainability Program, created to permit the extension of the life span of the USA's 104 nuclear reactors to 60 years. The licenses of almost half of the USA's reactors have been extended to 60 years as of 2008.[128] Two new "passive safety" AP1000 reactors are, as of 2013, being constructed at Vogtle Electric Generating Plant.

Public opinion about nuclear power varies widely between countries.[131][132] A poll by Gallup International (2011)[133] assessed public opinion in 47 countries. The poll was conducted following a tsunami and earthquake which caused an accident at the Fukushima nuclear power plant in Japan. 49% stated that they held favourable views about nuclear energy, while 43% held an unfavourable view.[134] Another global survey by Ipsos (2011)[135] assessed public opinion in 24 countries. Respondents to this survey showed a clear preference for renewable energy sources over coal and nuclear energy (refer to graph opposite).[2] Ipsos (2012)[136] found that solar and wind were viewed by the public as being more environmentally friendly and more viable long-term energy sources relative to nuclear power and natural gas. However, solar and wind were viewed as being less reliable relative to nuclear power and natural gas. In 2012 a poll done in the UK found that 63% of those surveyed support nuclear power, and with opposition to nuclear power at 11%.[137] In Germany, strong anti-nuclear sentiment led to eight of the seventeen operating reactors being permanently shut down following the March 2011 Fukushima nuclear disaster.[138]

Nuclear fusion research, in the form of the International Thermonuclear Experimental Reactor is underway. Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been. However, the extreme requirements for continuous reactions and plasma containment led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production was still believed to be unlikely before 2050.[139] Although rather than an either, or, issue economical fusion-fission hybrid reactors could be built before any attempt at this more demanding commercial "pure-fusion reactor"/DEMO reactor takes place.[140]

Coal to gas fuel switching

Most mitigation proposals imply—rather than directly state—an eventual reduction in global fossil fuel production. Also proposed are direct quotas on global fossil fuel production.[141][142]

Natural gas emits far fewer greenhouse gases (i.e. CO2 and methane—CH4) than coal when burned at power plants, but evidence has been emerging that this benefit could be completely negated by methane leakage at gas drilling fields and other points in the supply chain.

A study performed by the Environmental Protection Agency (EPA) and the Gas Research Institute (GRI) in 1997 sought to discover whether the reduction in carbon dioxide emissions from increased natural gas (predominantly methane) use would be offset by a possible increased level of methane emissions from sources such as leaks and emissions. The study concluded that the reduction in emissions from increased natural gas use outweighs the detrimental effects of increased methane emissions. More recent peer-reviewed studies have challenged the findings of this study, with researchers from the National Oceanic and Atmospheric Administration (NOAA) reconfirming findings of high rates of methane (CH4) leakage from natural gas fields.

A 2011 study[143] by noted climate research scientist, Tom Wigley,[144] found that while carbon dioxide (CO2) emissions from fossil fuel combustion may be reduced by using natural gas rather than coal to produce energy, it also found that additional methane (CH4) from leakage adds to the radiative forcing of the climate system, offsetting the reduction in CO2 forcing that accompanies the transition from coal to gas. The study looked at methane leakage from coal mining; changes in radiative forcing due to changes in the emissions of sulfur dioxide and carbonaceous aerosols; and differences in the efficiency of electricity production between coal- and gas-fired power generation. On balance, these factors more than offset the reduction in warming due to reduced CO2 emissions. When gas replaces coal there is additional warming out to 2,050 with an assumed leakage rate of 0%, and out to 2,140 if the leakage rate is as high as 10%. The overall effects on global-mean temperature over the 21st century, however, are small. Petron et al. (2013)[145] and Alvarez et al. (2012)[146] note that estimated that leakage from gas infrastructure is likely to be underestimated. These studies indicate that the exploitation of natural gas as a "cleaner" fuel is questionable. A 2014 meta-study of 20 years of natural gas technical literature shows that methane emissions are consistently underestimated but on a 100-year scale, the climate benefits of coal to gas fuel switching are likely larger than the negative effects of natural gas leakage.[147]

Heat pump

Outside unit of an air-source heat pump

A heat pump is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power to accomplish the work of transferring energy from the heat source to the heat sink.

While air conditioners and freezers are familiar examples of heat pumps, the term "heat pump" is more general and applies to many HVAC (heating, ventilating, and air conditioning) devices used for space heating or space cooling. When a heat pump is used for heating, it employs the same basic refrigeration-type cycle used by an air conditioner or a refrigerator, but in the opposite direction—releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground.[148] In heating mode, heat pumps are three to four times more efficient in their use of electric power than simple electrical resistance heaters.

It has been concluded that heat pumps are the single technology that could reduce the greenhouse gas emissions of households better than every other technology that is available on the market. With a market share of 30% and (potentially) clean electricity, heat pumps could reduce global CO2 emissions by 8% annually.[149] Using ground source heat pumps could reduce around 60% of the primary energy demand and 90% of CO2 emissions in Europe in 2050 and make handling high shares of renewable energy easier.[150] Using surplus renewable energy in heat pumps is regarded as the most effective household means to reduce global warming and fossil fuel depletion.[151]

With significant amounts of fossil fuel used in electricity production, demands on the electrical grid also generate greenhouse gases. Without a high share of low-carbon electricity, a domestic heat pump will produce more carbon emissions than using natural gas.[152]

Fossil fuel phase-out: carbon neutral and negative fuels

3,500–4,000 environmental activists blocking a coal mine in Germany to limit climate change (Ende Gelände 2016)

Fossil fuel may be phased-out with carbon-neutral and carbon-negative pipeline and transportation fuels created with power to gas and gas to liquids technologies.[153][154][155][156][157] Carbon dioxide from fossil fuel flue gas can be used to produce plastic lumber allowing carbon negative reforestation.[158]

Sinks and negative emissions

A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period, such as a growing forest. A negative carbon dioxide emission on the other hand is a permanent removal of carbon dioxide out of the atmosphere. Examples are direct air capture, enhanced weathering technologies such as storing it in geologic formations underground and biochar. These processes are sometimes considered as variations of sinks or mitigation,[159][160] and sometimes as geoengineering.[161] In combination with other mitigation measures, sinks in combination with negative carbon emissions are considered crucial for meeting the 350 ppm target.[162][163][164]

The Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC) notes that one third of humankind's annual emissions of CO2 are absorbed by the oceans.[165] However, this also leads to ocean acidification, with potentially significant impacts on marine life.[166] Acidification lowers the level of carbonate ions available for calcifying organisms to form their shells. These organisms include plankton species that contribute to the foundation of the Southern Ocean food web. However acidification may impact on a broad range of other physiological and ecological processes, such as fish respiration, larval development and changes in the solubility of both nutrients and toxins.[167]

Reforestation and afforestation

Transferring land rights to indigenous inhabitants is argued to efficiently conserve forests. Regrowth of forests on abandoned farmland restores more forest than that lost to deforestation.

Almost 20 percent (8 GtCO2/year) of total greenhouse-gas emissions were from deforestation in 2007. It is estimated that avoided deforestation reduces CO2 emissions at a rate of 1 tonne of CO2 per $1–5 in opportunity costs from lost agriculture. Reforestation could save at least another 1 GtCO2/year, at an estimated cost of $5–15/tCO2.[168] Afforestation is where there was previously no forest - such plantations are estimated to have to be prohibitively massive to be reduce emissions by itself.[169]

Transferring rights over land from public domain to its indigenous inhabitants is argued to be a cost effective strategy to conserve forests.[170] This includes the protection of such rights entitled in existing laws, such as India's Forest Rights Act.[170] The transferring of such rights in China, perhaps the largest land reform in modern times, has been argued to have increased forest cover.[171] In Brazil, forested areas given tenure to indigenous groups have even lower rates of clearing than national parks.[171] A 2016 report concludes that modest investments in indigenous land rights will generate economic, social, and environmental returns for the communities involved and for climate protection. The report quantifies the economic value of securing such rights, with a focus on the Amazon region.[172][173]

With increased intensive agriculture and urbanization, there is an increase in the amount of abandoned farmland. By some estimates, for every half a hectare of original old-growth forest cut down, more than 20 hectares of new secondary forests are growing, even though they do not have the same biodiversity as the original forests and original forests store 60% more carbon than these new secondary forests.[174][175] According to a study in Science, promoting regrowth on abandoned farmland could offset years of carbon emissions.[176]

Avoided desertification

Managed grazing methods are argued to be able to restore grasslands, thereby significantly decreasing atmospheric CO2 levels.[177]

Restoring grasslands store CO2 from the air into plant material. Grazing livestock, usually not left to wander, would eat the grass and would minimize any grass growth. However, grass left alone would eventually grow to cover its own growing buds, preventing them from photosynthesizing and the dying plant would stay in place.[178] A method proposed to restore grasslands uses fences with many small paddocks and moving herds from one paddock to another after a day a two in order to mimick natural grazers and allowing the grass to grow optimally.[178][179][180] Additionally, when part of leaf matter is consumed by a herding animal, a corresponding amount of root matter is sloughed off too as it would not be able to sustain the previous amount of root matter and while most of the lost root matter would rot and enter the atmosphere, part of the carbon is sequestered into the soil.[178] It is estimated that increasing the carbon content of the soils in the world's 3.5 billion hectares of agricultural grassland by 1% would offset nearly 12 years of CO2 emissions.[178] Allan Savory, as part of holistic management, claims that while large herds are often blamed for desertification, prehistoric lands supported large or larger herds and areas where herds were removed in the United States are still desertifying.[177]

Carbon capture and storage

Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a coal-fired plant

Carbon capture and storage (CCS) is a method to mitigate climate change by capturing carbon dioxide (CO2) from large point sources such as power plants and subsequently storing it away safely instead of releasing it into the atmosphere. The IPCC estimates that the costs of halting global warming would double without CCS.[181] The International Energy Agency says CCS is "the most important single new technology for CO2 savings" in power generation and industry.[182] Though it requires up to 40% more energy to run a CCS coal power plant than a regular coal plant, CCS could potentially capture about 90% of all the carbon emitted by the plant.[182] Norway's Sleipner gas field, beginning in 1996, stores almost a million tons of CO2 a year to avoid penalties in producing natural gas with unusually high levels of CO2.[183][182] As of late 2011, the total planned CO2 storage capacity of all 14 projects in operation or under construction is over 33 million tonnes a year. This is broadly equivalent to preventing the emissions from more than six million cars from entering the atmosphere each year.[184] According to a Sierra Club analysis, the US coal fired Kemper Project due to be online in 2017, is the most expensive power plant ever built for the watts of electricity it will generate.[185]

Enhanced weathering

Enhanced weathering is the removal of carbon from the air into the earth, enhancing the natural carbon cycle where carbon is mineralized into rock. The CarbFix project couples with carbon capture and storage in power plants to turn carbon dioxide into stone in a relatively short period of two years, addressing the common concern of leakage in CCS projects. While this project used basalt rocks, olivine has also shown promise.[181]

Geoengineering

Geoengineering is seen by Olivier Sterck as an alternative to mitigation and adaptation, but by Gernot Wagner as an entirely separate response to climate change.[186][187] In a literature assessment, Barker et al. (2007) described geoengineering as a type of mitigation policy.[188] IPCC (2007) concluded that geoengineering options, such as ocean fertilization to remove CO2 from the atmosphere, remained largely unproven.[189] It was judged that reliable cost estimates for geoengineering had not yet been published.

Chapter 28 of the National Academy of Sciences report Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base (1992) defined geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry."[190] They evaluated a range of options to try to give preliminary answers to two questions: can these options work and could they be carried out with a reasonable cost. They also sought to encourage discussion of a third question — what adverse side effects might there be. The following types of option were examined: reforestation, increasing ocean absorption of carbon dioxide (carbon sequestration) and screening out some sunlight. NAS also argued "Engineered countermeasures need to be evaluated but should not be implemented without broad understanding of the direct effects and the potential side effects, the ethical issues, and the risks.".[190] In July 2011 a report by the United States Government Accountability Office on geoengineering found that "[c]limate engineering technologies do not now offer a viable response to global climate change."[191]

Carbon dioxide removal

Carbon dioxide removal has been proposed as a method of reducing the amount of radiative forcing. A variety of means of artificially capturing and storing carbon, as well as of enhancing natural sequestration processes, are being explored. The main natural process is photosynthesis by plants and single-celled organisms (see biosequestration). Artificial processes vary, and concerns have been expressed about the long-term effects of some of these processes.[192]

It is notable that the availability of cheap energy and appropriate sites for geological storage of carbon may make carbon dioxide air capture viable commercially. It is, however, generally expected that carbon dioxide air capture may be uneconomic when compared to carbon capture and storage from major sources — in particular, fossil fuel powered power stations, refineries, etc. As in the case of the US Kemper Project with carbon capture, costs of energy produced will grow significantly. However, captured CO2 can be used to force more crude oil out of oil fields, as Statoil and Shell have made plans to do.[193] CO2 can also be used in commercial greenhouses, giving an opportunity to kick-start the technology. Some attempts have been made to use algae to capture smokestack emissions,[194] notably the GreenFuel Technologies Corporation, who have now shut down operations.[195]

Solar radiation management

The main purpose of solar radiation management seek to reflect sunlight and thus reduce global warming. The ability of stratospheric sulfate aerosols to create a global dimming effect has made them a possible candidate for use in climate engineering projects.[196]

Non-CO2 greenhouse gases

CO2 is not the only GHG relevant to mitigation,[197] and governments have acted to regulate the emissions of other GHGs emitted by human activities (anthropogenic GHGs). The emissions caps agreed to by most developed countries under the Kyoto Protocol regulate the emissions of almost all the anthropogenic GHGs.[198] These gases are CO2, methane (CH4), nitrous oxide (N2O), the hydrofluorocarbons (HFC), perfluorocarbons (PFC), and sulfur hexafluoride (SF6).

Stabilizing the atmospheric concentrations of the different anthropogenic GHGs requires an understanding of their different physical properties. Stabilization depends both on how quickly GHGs are added to the atmosphere and how fast they are removed. The rate of removal is measured by the atmospheric lifetime of the GHG in question (see the main GHG article for a list). Here, the lifetime is defined as the time required for a given perturbation of the GHG in the atmosphere to be reduced to 37% of its initial amount.[8] Methane has a relatively short atmospheric lifetime of about 12 years, while N2O's lifetime is about 110 years. For methane, a reduction of about 30% below current emission levels would lead to a stabilization in its atmospheric concentration, while for N2O, an emissions reduction of more than 50% would be required.[8]

Methane is a significantly more potent greenhouse gas than carbon dioxide in the amount of heat it can trap, especially in the short term.[199] Burning one molecule of methane generates one molecule of carbon dioxide, indicating there may be no net benefit in using gas as a fuel source.[143][145] Reducing the amount of waste methane produced in the first place and moving away from use of gas as a fuel source will have a greater beneficial impact, as might other approaches to productive use of otherwise-wasted methane. In terms of prevention, vaccines are being developed in Australia to reduce the significant global warming contributions from methane released by livestock via flatulence and eructation.[200]

Another physical property of the anthropogenic GHGs relevant to mitigation is the different abilities of the gases to trap heat (in the form of infrared radiation). Some gases are more effective at trapping heat than others, e.g., SF6 is 22,200 times more effective a GHG than CO2 on a per-kilogram basis.[201] A measure for this physical property is the global warming potential (GWP), and is used in the Kyoto Protocol.[202]

Although not designed for this purpose, the Montreal Protocol has probably benefited climate change mitigation efforts.[203] The Montreal Protocol is an international treaty that has successfully reduced emissions of ozone-depleting substances (for example, CFCs), which are also greenhouse gases.

By sector

The Tesla Roadster (2008) emits no tailpipe emissions, uses lithium ion batteries to achieve 220 mi (350 km) per charge, while also capable of going 0–60 in under 4 seconds.
Bicycles have almost no carbon footprint compared to cars, and canal transport may represent a positive option for certain types of freight in the 21st century.[204]

Transport

Transportation emissions account for roughly 1/4 of emissions worldwide, and are even more important in terms of impact in developed nations especially in North America and Australia. Many citizens of countries like the United States and Canada who drive personal cars often, see well over half of their climate change impact stemming from the emissions produced from their cars. Modes of mass transportation such as bus, light rail (metro, subway, etc.), and long-distance rail are far and away the most energy-efficient means of motorized transportation for passengers, able to use in many cases over twenty times less energy per person-distance than a personal automobile. Modern energy-efficient technologies, such as plug-in hybrid electric vehicles and carbon-neutral synthetic gasoline & Jet fuel may also help to reduce the consumption of petroleum, land use changes and emissions of carbon dioxide. Utilizing rail transport, especially electric rail, over the far less efficient air transport and truck transport significantly reduces emissions.[205][206] With the use of electric trains and cars in transportation there is the opportunity to run them with low-carbon power, producing far fewer emissions.

Urban planning

Effective urban planning to reduce sprawl aims to decrease Vehicle Miles Travelled (VMT), lowering emissions from transportation. Personal cars are extremely inefficient at moving passengers, while public transport and bicycles are many times more efficient (as is the simplest form of human transportation, walking). All of these are encouraged by urban/community planning and are an effective way to reduce greenhouse gas emissions. Between 1982 and 1997, the amount of land consumed for urban development in the United States increased by 47 percent while the nation's population grew by only 17 percent.[207] Inefficient land use development practices have increased infrastructure costs as well as the amount of energy needed for transportation, community services, and buildings.

At the same time, a growing number of citizens and government officials have begun advocating a smarter approach to land use planning. These smart growth practices include compact community development, multiple transportation choices, mixed land uses, and practices to conserve green space. These programs offer environmental, economic, and quality-of-life benefits; and they also serve to reduce energy usage and greenhouse gas emissions.

Approaches such as New Urbanism and transit-oriented development seek to reduce distances travelled, especially by private vehicles, encourage public transit and make walking and cycling more attractive options. This is achieved through "medium-density", mixed-use planning and the concentration of housing within walking distance of town centers and transport nodes.

Smarter growth land use policies have both a direct and indirect effect on energy consuming behavior. For example, transportation energy usage, the number one user of petroleum fuels, could be significantly reduced through more compact and mixed use land development patterns, which in turn could be served by a greater variety of non-automotive based transportation choices.

Building design

Emissions from housing are substantial,[208] and government-supported energy efficiency programmes can make a difference.[209]

For institutions of higher learning in the United States, greenhouse gas emissions depend primarily on total area of buildings and secondarily on climate.[210] If climate is not taken into account, annual greenhouse gas emissions due to energy consumed on campuses plus purchased electricity can be estimated with the formula, E=aSb, where a =0.001621 metric tonnes of CO2 equivalent/square foot or 0.0241 metric tonnes of CO2 equivalent/square meter and b= 1.1354.[211]

New buildings can be constructed using passive solar building design, low-energy building, or zero-energy building techniques, using renewable heat sources. Existing buildings can be made more efficient through the use of insulation, high-efficiency appliances (particularly hot water heaters and furnaces), double- or triple-glazed gas-filled windows, external window shades, and building orientation and siting. Renewable heat sources such as shallow geothermal and passive solar energy reduce the amount of greenhouse gasses emitted. In addition to designing buildings which are more energy-efficient to heat, it is possible to design buildings that are more energy-efficient to cool by using lighter-coloured, more reflective materials in the development of urban areas (e.g. by painting roofs white) and planting trees.[212][213] This saves energy because it cools buildings and reduces the urban heat island effect thus reducing the use of air conditioning.

Agriculture

According to the EPA, agricultural soil management practices can lead to production and emission of nitrous oxide (N2O), a major greenhouse gas and air pollutant. Activities that can contribute to N
2
O
emissions include fertilizer usage, irrigation, and tillage. The management of soils accounts for over half of the emissions from the Agriculture sector. Cattle livestocks account for one third of emissions, through methane emissions. Manure management and rice cultivation also produce gaseous emissions.[214]

Methods that significantly enhance carbon sequestration in soil include no-till farming, residue mulching, cover cropping, and crop rotation, all of which are more widely used in organic farming than in conventional farming.[215][216] Because only 5% of US farmland currently uses no-till and residue mulching, there is a large potential for carbon sequestration.[217]

A 2015 study found that farming can deplete soil carbon and render soil incapable of supporting life; however, the study also showed that conservation farming can protect carbon in soils, and repair damage over time.[218]

The farming practise of cover crops has been recognized as climate-smart agriculture by the White House.[219]

In Europe the estimation of the current 0–30 cm SOC stock of agricultural soils was 17.63 Gt.[220] In a subsequent study, authors estimated the best management practices to mitigate soil organic carbon: conversion of arable land to grassland (and vice versa), straw incorporation, reduced tillage, straw incorporation combined with reduced tillage, ley cropping system and cover crops.[221]

Societal controls

Another method being examined is to make carbon a new currency by introducing tradeable "personal carbon credits". The idea being it will encourage and motivate individuals to reduce their 'carbon footprint' by the way they live. Each citizen will receive a free annual quota of carbon that they can use to travel, buy food, and go about their business. It has been suggested that by using this concept it could actually solve two problems; pollution and poverty, old age pensioners will actually be better off because they fly less often, so they can cash in their quota at the end of the year to pay heating bills and so forth.[cần dẫn nguồn]

Population

Population density by country

Various organizations promote population control as a means for mitigating global warming.[222][223][224][225][226] Proposed measures include improving access to family planning and reproductive health care and information, reducing natalistic politics, public education about the consequences of continued population growth, and improving access of women to education and economic opportunities.

Population control efforts are impeded by there being somewhat of a taboo in some countries against considering any such efforts.[227] Also, various religions discourage or prohibit some or all forms of birth control.

Population size has a different per capita effect on global warming in different countries, since the per capita production of anthropogenic greenhouse gases varies greatly by country.[228]

Costs and benefits

Costs

The Stern Review proposes stabilising the concentration of greenhouse-gas emissions in the atmosphere at a maximum of 550ppm CO2e by 2050. The Review estimates that this would mean cutting total greenhouse-gas emissions to three quarters of 2007 levels. The Review further estimates that the cost of these cuts would be in the range −1.0 to +3.5% of World GDP, (i.e. GWP), with an average estimate of approximately 1%.[168] Stern has since revised his estimate to 2% of GWP.[229] For comparison, the Gross World Product (GWP) at PPP was estimated at $74.5 trillion in 2010,[230] thus 2% is approximately $1.5 trillion. The Review emphasises that these costs are contingent on steady reductions in the cost of low-carbon technologies. Mitigation costs will also vary according to how and when emissions are cut: early, well-planned action will minimise the costs.[168]

One way of estimating the cost of reducing emissions is by considering the likely costs of potential technological and output changes. Policy makers can compare the marginal abatement costs of different methods to assess the cost and amount of possible abatement over time. The marginal abatement costs of the various measures will differ by country, by sector, and over time.[168]

Benefits

Total extreme weather cost and number of events costing more than $1 billion in the United States from 1980 to 2011

Yohe et al. (2007) assessed the literature on sustainability and climate change.[231] With high confidence, they suggested that up to the year 2050, an effort to cap greenhouse gas (GHG) emissions at 550 ppm would benefit developing countries significantly. This was judged to be especially the case when combined with enhanced adaptation. By 2100, however, it was still judged likely that there would be significant effects of global warming. This was judged to be the case even with aggressive mitigation and significantly enhanced adaptive capacity.

Sharing

One of the aspects of mitigation is how to share the costs and benefits of mitigation policies. There is no scientific consensus over how to share these costs and benefits (Toth et al., 2001).[232] In terms of the politics of mitigation, the UNFCCC's ultimate objective is to stabilize concentrations of GHG in the atmosphere at a level that would prevent "dangerous" climate change (Rogner et al., 2007).[233]

GHG emissions are an important correlate of wealth, at least at present (Banuri et al., 1996, pp. 91–92).[234] Wealth, as measured by per capita income (i.e., income per head of population), varies widely between different countries. Activities of the poor that involve emissions of GHGs are often associated with basic needs, such as heating to stay tolerably warm. In richer countries, emissions tend to be associated with things like cars, central heating, etc. The impacts of cutting emissions could therefore have different impacts on human welfare according to wealth.

Distributing emissions abatement costs

There have been different proposals on how to allocate responsibility for cutting emissions (Banuri et al., 1996, pp. 103–105):[234]

  • Egalitarianism: this system interprets the problem as one where each person has equal rights to a global resource, i.e., polluting the atmosphere.
  • Basic needs: this system would have emissions allocated according to basic needs, as defined according to a minimum level of consumption. Consumption above basic needs would require countries to buy more emission rights. From this viewpoint, developing countries would need to be at least as well off under an emissions control regime as they would be outside the regime.
  • Proportionality and polluter-pays principle: Proportionality reflects the ancient Aristotelian principle that people should receive in proportion to what they put in, and pay in proportion to the damages they cause. This has a potential relationship with the "polluter-pays principle", which can be interpreted in a number of ways:
    • Historical responsibilities: this asserts that allocation of emission rights should be based on patterns of past emissions. Two-thirds of the stock of GHGs in the atmosphere at present is due to the past actions of developed countries (Goldemberg et al., 1996, p. 29).[235]
    • Comparable burdens and ability to pay: with this approach, countries would reduce emissions based on comparable burdens and their ability to take on the costs of reduction. Ways to assess burdens include monetary costs per head of population, as well as other, more complex measures, like the UNDP's Human Development Index.
    • Willingness to pay: with this approach, countries take on emission reductions based on their ability to pay along with how much they benefit from reducing their emissions.

Specific proposals

  • Ad hoc: Lashof (1992) and Cline (1992) (referred to by Banuri et al., 1996, p. 106),[234] for example, suggested that allocations based partly on GNP could be a way of sharing the burdens of emission reductions. This is because GNP and economic activity are partially tied to carbon emissions.
  • Equal per capita entitlements: this is the most widely cited method of distributing abatement costs, and is derived from egalitarianism (Banuri et al., 1996, pp. 106–107). This approach can be divided into two categories. In the first category, emissions are allocated according to national population. In the second category, emissions are allocated in a way that attempts to account for historical (cumulative) emissions.
  • Status quo: with this approach, historical emissions are ignored, and current emission levels are taken as a status quo right to emit (Banuri et al., 1996, p. 107). An analogy for this approach can be made with fisheries, which is a common, limited resource. The analogy would be with the atmosphere, which can be viewed as an exhaustible natural resource (Goldemberg et al., 1996, p. 27).[235] In international law, one state recognized the long-established use of another state's use of the fisheries resource. It was also recognized by the state that part of the other state's economy was dependent on that resource.

Governmental and intergovernmental action

Bringing down emissions of greenhouse gases asks a good deal of people, not least that they accept the science of climate change. It requires them to make sacrifices today so that future generations will suffer less, and to weigh the needs of people who are living far away.

The Economist, 28 November 2015[236]

Many countries, both developing and developed, are aiming to use cleaner technologies (World Bank, 2010, p. 192).[237] Use of these technologies aids mitigation and could result in substantial reductions in CO2 emissions. Policies include targets for emissions reductions, increased use of renewable energy, and increased energy efficiency. It is often argued that the results of climate change are more damaging in poor nations, where infrastructures are weak and few social services exist. The Commitment to Development Index is one attempt to analyze rich country policies taken to reduce their disproportionate use of the global commons. Countries do well if their greenhouse gas emissions are falling, if their gas taxes are high, if they do not subsidize the fishing industry, if they have a low fossil fuel rate per capita, and if they control imports of illegally cut tropical timber.

Kyoto Protocol

The main current international agreement on combating climate change is the Kyoto Protocol. On the 11th of December 1997 it was implemented by the 3rd conference of parties, which was coming together in kyoto, which came into force on 16 February 2005. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that have ratified this protocol have committed to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases. For Kyoto reporting, governments are obliged to be told on the present state of the countries forests and the related ongoing processes.

Temperature targets

Refer to caption and image description
The graph on the right shows three "pathways" to meet the UNFCCC's 2 °C target, labelled "global technology", "decentralised solutions", and "consumption change". Each pathway shows how various measures (e.g., improved energy efficiency, increased use of renewable energy) could contribute to emissions reductions. Image credit: PBL Netherlands Environmental Assessment Agency.[238]

Actions to mitigate climate change are sometimes based on the goal of achieving a particular temperature target. One of the targets that has been suggested is to limit the future increase in global mean temperature (global warming) to below 2 °C, relative to the pre-industrial level.[239][240] The 2 °C target was adopted in 2010 by Parties to the United Nations Framework Convention on Climate Change.[241] Most countries of the world are Parties to the UNFCCC.[242] The target had been adopted in 1996 by the European Union Council.[243]

Feasibility of 2 °C

Temperatures have increased by 0.8 °C compared to the pre-industrial level, and another 0.5–0.7 °C is already committed.[244] The 2 °C rise is typically associated in climate models with a carbon dioxide equivalent concentration of 400–500 ppm by volume; the current (January 2015) level of carbon dioxide alone is 400 ppm by volume, and rising at 1–3 ppm annually. Hence, to avoid a very likely breach of the 2 °C target, CO2 levels would have to be stabilised very soon; this is generally regarded as unlikely, based on current programs in place to date.[245][246] The importance of change is illustrated by the fact that world economic energy efficiency is improving at only half the rate of world economic growth.[247]

Views in the literature

There is disagreement among experts over whether or not the 2 °C target can be met.[248][249] For example, according to Anderson and Bows (2011),[250] "there is little to no chance" of meeting the target. On the other hand, according to Alcamo et al. (2013):[251]

  • Policies adopted by parties to the UNFCCC are too weak to meet a 2 or 1.5 °C target. However, these targets might still be achievable if more stringent mitigation policies are adopted immediately.
  • Cost-effective 2 °C scenarios project annual global greenhouse gas emissions to peak before the year 2020, with deep cuts in emissions thereafter, leading to a reduction in 2050 of 41% compared to 1990 levels.[252]
Discussion on other targets

Scientific analysis can provide information on the impacts of climate change and associated policies, such as reducing GHG emissions. However, deciding what policies are best requires value judgements.[253] For example, limiting global warming to 1 °C relative to pre-industrial levels may help to reduce climate change damages more than a 2 °C limit.[254] However, a 1 °C limit may be more costly to achieve than a 2 °C limit.[255]

According to some analysts, the 2 °C "guardrail" is inadequate for the needed degree and timeliness of mitigation.[256] On the other hand, some economic studies suggest more modest mitigation policies.[257] For example, the emissions reductions proposed by Nordhaus (2010)[258] might lead to global warming (in the year 2100) of around 3 °C, relative to pre-industrial levels.

Official long-term target of 1.5 °C

In 2015, two official UNFCCC scientific expert bodies came to the conclusion that, "in some regions and vulnerable ecosystems, high risks are projected even for warming above 1.5°C".[259] This expert position was, together with the strong diplomatic voice of the poorest countries and the island nations in the Pacific, the driving force leading to the decision of the Paris Conference 2015, to lay down this 1.5 °C long-term target on top of the existing 2 °C goal.[260]

Encouraging use changes

Emissions tax

An emissions tax on greenhouse gas emissions requires individual emitters to pay a fee, charge or tax for every tonne of greenhouse gas released into the atmosphere.[261] Most environmentally related taxes with implications for greenhouse gas emissions in OECD countries are levied on energy products and motor vehicles, rather than on CO2 emissions directly.[261]

Emission taxes can be both cost-effective and environmentally effective.[261] Difficulties with emission taxes include their potential unpopularity, and the fact that they cannot guarantee a particular level of emissions reduction.[261] Emissions or energy taxes also often fall disproportionately on lower income classes. In developing countries, institutions may be insufficiently developed for the collection of emissions fees from a wide variety of sources.[261]

Subsidies

According to Mark Z. Jacobson, a program of subsidization balanced against expected flood costs could pay for conversion to 100% renewable power by 2030.[262] Jacobson, and his colleague Mark Delucchi, suggest that the cost to generate and transmit power in 2020 will be less than 4 cents per kilowatt hour (in 2007 dollars) for wind, about 4 cents for wave and hydroelectric, from 4 to 7 cents for geothermal, and 8 cents per kWh for solar, fossil, and nuclear power.[263]

Investment

Another indirect method of encouraging uses of renewable energy, and pursue sustainability and environmental protection, is that of prompting investment in this area through legal means, something that is already being done at national level as well as in the field of international investment.[264]

Carbon emissions trading

With the creation of a market for trading carbon dioxide emissions within the Kyoto Protocol, it is likely that London financial markets will be the centre for this potentially highly lucrative business; the New York and Chicago stock markets may have a lower trade volume than expected as long as the US maintains its rejection of the Kyoto.[265]

However, emissions trading may delay the phase-out of fossil fuels.[266]

In the north-east United States, a successful cap and trade program has shown potential for this solution.[267]

The European Union Emission Trading Scheme (EU ETS)[268] is the largest multi-national, greenhouse gas emissions trading scheme in the world. It commenced operation on 1 January 2005, and all 28 member states of the European Union participate in the scheme which has created a new market in carbon dioxide allowances estimated at 35 billion Euros (US$43 billion) per year.[269] The Chicago Climate Exchange was the first (voluntary) emissions market, and is soon to be followed by Asia's first market (Asia Carbon Exchange). A total of 107 million metric tonnes of carbon dioxide equivalent have been exchanged through projects in 2004, a 38% increase relative to 2003 (78 Mt CO2e).[270]

Twenty three multinational corporations have come together in the G8 Climate Change Roundtable, a business group formed at the January 2005 World Economic Forum. The group includes Ford, Toyota, British Airways, and BP. On 9 June 2005 the Group published a statement[271] stating that there was a need to act on climate change and claiming that market-based solutions can help. It called on governments to establish "clear, transparent, and consistent price signals" through "creation of a long-term policy framework" that would include all major producers of greenhouse gases.

The Regional Greenhouse Gas Initiative is a proposed carbon trading scheme being created by nine North-eastern and Mid-Atlantic American states; Connecticut, Delaware, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont. The scheme was due to be developed by April 2005 but has not yet been completed.

Implementation

Implementation puts into effect climate change mitigation strategies and targets. These can be targets set by international bodies or voluntary action by individuals or institutions. This is the most important, expensive and least appealing aspect of environmental governance.[272]

Funding

Implementation requires funding sources but is often beset by disputes over who should provide funds and under what conditions.[272] A lack of funding can be a barrier to successful strategies as there are no formal arrangements to finance climate change development and implementation.[273] Funding is often provided by nations, groups of nations and increasingly NGO and private sources. These funds are often channelled through the Global Environmental Facility (GEF). This is an environmental funding mechanism in the World Bank which is designed to deal with global environmental issues.[272] The GEF was originally designed to tackle four main areas: biological diversity, climate change, international waters and ozone layer depletion, to which land degradation and persistent organic pollutant were added. The GEF funds projects that are agreed to achieve global environmental benefits that are endorsed by governments and screened by one of the GEF's implementing agencies.[274]

Problems

There are numerous issues which result in a current perceived lack of implementation.[272] It has been suggested that the main barriers to implementation are Uncertainty, Fragmentation, Institutional void, Short time horizon of policies and politicians and Missing motives and willingness to start adapting. The relationships between many climatic processes can cause large levels of uncertainty as they are not fully understood and can be a barrier to implementation. When information on climate change is held between the large numbers of actors involved it can be highly dispersed, context specific or difficult to access causing fragmentation to be a barrier. Institutional void is the lack of commonly accepted rules and norms for policy processes to take place, calling into question the legitimacy and efficacy of policy processes. The Short time horizon of policies and politicians often means that climate change policies are not implemented in favour of socially favoured societal issues. Statements are often posed to keep the illusion of political action to prevent or postpone decisions being made. Missing motives and willingness to start adapting is a large barrier as it prevents any implementation.[273] The issues that arise with a system which involves international government cooperation, such as cap and trade, could potentially be improved with a polycentric approach where the rules are enforced by many small sections of authority as opposed to one overall enforcement agency.[275] Concerns about metal requirement and/or availability for essential decarbonization technoloqies such as photovoltaics, nuclear power, and (plug-in hybrid) electric vehicles have also been expressed as obstacles.[276]

Occurrence

Despite a perceived lack of occurrence, evidence of implementation is emerging internationally. Some examples of this are the initiation of NAPA's and of joint implementation. Many developing nations have made National Adaptation Programs of Action (NAPAs) which are frameworks to prioritize adaption needs.[277] The implementation of many of these is supported by GEF agencies.[278] Many developed countries are implementing 'first generation' institutional adaption plans particularly at the state and local government scale.[277] There has also been a push towards joint implementation between countries by the UNFCCC as this has been suggested as a cost-effective way for objectives to be achieved.[279]

Territorial policies

Carbon emission trading and carbon tax around the world
  Emission trading implemented
  Emission trading scheduled
  Carbon tax implemented
  Carbon tax scheduled
  Emission trading or carbon tax under consideration

United States

Efforts to reduce greenhouse gas emissions by the United States include energy policies which encourage efficiency through programs like Energy Star, Commercial Building Integration, and the Industrial Technologies Program.[280] On 12 November 1998, Vice President Al Gore symbolically signed the Kyoto Protocol, but he indicated participation by the developing nations was necessary prior its being submitted for ratification by the United States Senate.[281]

In 2007, Transportation Secretary Mary Peters, with White House approval, urged governors and dozens of members of the House of Representatives to block California's first-in-the-nation limits on greenhouse gases from cars and trucks, according to e-mails obtained by Congress.[282] The US Climate Change Science Program is a group of about twenty federal agencies and US Cabinet Departments, all working together to address global warming.

The Bush administration pressured American scientists to suppress discussion of global warming, according to the testimony of the Union of Concerned Scientists to the Oversight and Government Reform Committee of the US House of Representatives.[283][284] "High-quality science" was "struggling to get out," as the Bush administration pressured scientists to tailor their writings on global warming to fit the Bush administration's skepticism, in some cases at the behest of an ex-oil industry lobbyist. "Nearly half of all respondents perceived or personally experienced pressure to eliminate the words 'climate change,' 'global warming' or other similar terms from a variety of communications." Similarly, according to the testimony of senior officers of the Government Accountability Project, the White House attempted to bury the report "National Assessment of the Potential Consequences of Climate Variability and Change," produced by US scientists pursuant to US law.[285] Some US scientists resigned their jobs rather than give in to White House pressure to underreport global warming.[283]

In the absence of substantial federal action, state governments have adopted emissions-control laws such as the Regional Greenhouse Gas Initiative in the Northeast and the Global Warming Solutions Act of 2006 in California.[286]

Developing countries

In order to reconcile economic development with mitigating carbon emissions, developing countries need particular support, both financial and technical. One of the means of achieving this is the Kyoto Protocol's Clean Development Mechanism (CDM). The World Bank's Prototype Carbon Fund[287] is a public private partnership that operates within the CDM.

An important point of contention, however, is how overseas development assistance not directly related to climate change mitigation is affected by funds provided to climate change mitigation.[288] One of the outcomes of the UNFCC Copenhagen Climate Conference was the Copenhagen Accord, in which developed countries promised to provide US$30 million between 2010 and 2012 of new and additional resources.[288] Yet it remains unclear what exactly the definition of additional is and the European Commission has requested its member states to define what they understand to be additional, and researchers at the Overseas Development Institute have found four main understandings:[288]

  1. Climate finance classified as aid, but additional to (over and above) the '0.7%' ODA target;
  2. Increase on previous year's Official Development Assistance (ODA) spent on climate change mitigation;
  3. Rising ODA levels that include climate change finance but where it is limited to a specified percentage; and
  4. Increase in climate finance not connected to ODA.

The main point being that there is a conflict between the OECD states budget deficit cuts, the need to help developing countries adapt to develop sustainably and the need to ensure that funding does not come from cutting aid to other important Millennium Development Goals.[288]

However, none of these initiatives suggest a quantitative cap on the emissions from developing countries. This is considered as a particularly difficult policy proposal as the economic growth of developing countries are proportionally reflected in the growth of greenhouse emissions. Critics[ai nói?] of mitigation often argue that, the developing countries' drive to attain a comparable living standard to the developed countries would doom the attempt at mitigation of global warming. Critics[ai nói?] also argue that holding down emissions would shift the human cost of global warming from a general one to one that was borne most heavily by the poorest populations on the planet.

In an attempt to provide more opportunities for developing countries to adapt clean technologies, UNEP and WTO urged the international community to reduce trade barriers and to conclude the Doha trade round "which includes opening trade in environmental goods and services".[289]

Non-governmental approaches

While many of the proposed methods of mitigating global warming require governmental funding, legislation and regulatory action, individuals and businesses can also play a part in the mitigation effort.

Choices in personal actions and business operations

Environmental groups encourage individual action against global warming, often aimed at the consumer. Common recommendations include lowering home heating and cooling usage, burning less gasoline, supporting renewable energy sources, buying local products to reduce transportation, turning off unused devices, and various others.

A geophysicist at Utrecht University has urged similar institutions to hold the vanguard in voluntary mitigation, suggesting the use of communications technologies such as videoconferencing to reduce their dependence on long-haul flights.[290]

Air travel and shipment

In 2008, climate scientist Kevin Anderson raised concern about the growing effect of rapidly increasing global air transport on the climate in a paper,[291] and a presentation,[292] suggesting that reversing this trend is necessary to reduce emissions.

Part of the difficulty is that when aviation emissions are made at high altitude, the climate impacts are much greater than otherwise. Others have been raising the related concerns of the increasing hypermobility of individuals, whether traveling for business or pleasure, involving frequent and often long distance air travel, as well as air shipment of goods.[293]

Business opportunities and risks

On 9 May 2005 Jeff Immelt, the chief executive of General Electric (GE), announced plans to reduce GE's global warming related emissions by one percent by 2012. "GE said that given its projected growth, those emissions would have risen by 40 percent without such action."[294]

On 21 June 2005 a group of leading airlines, airports, and aerospace manufacturers pledged to work together to reduce the negative environmental impact of aviation, including limiting the impact of air travel on climate change by improving fuel efficiency and reducing carbon dioxide emissions of new aircraft by fifty percent per seat kilometre by 2020 from 2000 levels. The group aims to develop a common reporting system for carbon dioxide emissions per aircraft by the end of 2005, and pressed for the early inclusion of aviation in the European Union's carbon emission trading scheme.[295]

Investor response

Climate change is also a concern for large institutional investors who have a long term time horizon and potentially large exposure to the negative impacts of global warming because of the large geographic footprint of their multi-national holdings. SRI (Socially responsible investing) Funds allow investors to invest in funds that meet high ESG (environmental, social, governance) standards as such funds invest in companies that are aligned with these goals.[296] Proxy firms can be used to draft guidelines for investment managers that take these concerns into account.[297]

Legal action

In some countries, those affected by climate change may be able to sue major producers. Attempts at litigation have been initiated by entire peoples such as Palau[298] and the Inuit,[299] as well as non-governmental organizations such as the Sierra Club.[300] Although proving that particular weather events are due specifically to global warming may never be possible,[301] methodologies have been developed to show the increased risk of such events caused by global warming.[302]

For a legal action for negligence (or similar) to succeed, "Plaintiffs ... must show that, more probably than not, their individual injuries were caused by the risk factor in question, as opposed to any other cause. This has sometimes been translated to a requirement of a relative risk of at least two."[303] Another route (though with little legal bite) is the World Heritage Convention, if it can be shown that climate change is affecting World Heritage Sites like Mount Everest.[304][305]

Besides countries suing one another, there are also cases where people in a country have taken legal steps against their own government. Legal action for instance has been taken to try to force the US Environmental Protection Agency to regulate greenhouse gas emissions under the Clean Air Act,[306] and against the Export-Import Bank and OPIC for failing to assess environmental impacts (including global warming impacts) under NEPA.[cần dẫn nguồn]

In the Netherlands and Belgium, organisations such as Urgenda[307][308][309] and the vzw Klimaatzaak in Belgium[310][311] have also sued their governments as they believe their governments aren't meeting the emission reductions they agreed to. Urgenda have already won their case against the Dutch government.[cần dẫn nguồn]

According to a 2004 study commissioned by Friends of the Earth, ExxonMobil, and its predecessors caused 4.7 to 5.3 percent of the world's man-made carbon dioxide emissions between 1882 and 2002. The group suggested that such studies could form the basis for eventual legal action.[312]

In 2015, Exxon received a subpoena. According to the Washington Post and confirmed by the company, the attorney general of New York, Eric Schneiderman, opened an investigation into the possibility that the company had misled the public and investors about the risks of climate change.[313]

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