View source for Sustainable energy

{{Short description|Energy that responsibly meets social, economic, and environmental needs}}
{{Redirect|Green power}}
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{{Use dmy dates|date=September 2023}}
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| image1            = Andasol Guadix 4.jpg
| alt1              = Concentrated solar power parabolic troughs in the distance arranged in rectangles shining on a flat plain with snowy mountains in the background
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| footer            = Sustainable energy examples: [[Concentrated solar power]] with [[Thermal energy storage#Molten salt technology|molten salt heat storage]] in Spain; [[wind energy]] in South Africa; electrified [[public transport]] in Singapore; and [[clean cooking]] in Ethiopia.
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[[Energy system|Energy]] is [[sustainability|sustainable]] if it "meets the needs of the present without compromising the ability of [[future generations]] to meet their own needs."{{Sfn|Kutscher|Milford|Kreith|2019|pp=5–6}}<ref>{{cite journal |last1=Zhang |first1=Wei |last2=Li |first2=Binshuai |last3=Xue |first3=Rui |last4=Wang |first4=Chengcheng |last5=Cao |first5=Wei |title=A systematic bibliometric review of clean energy transition: Implications for low-carbon development |journal=[[PLOS One|PLOS ONE]] |date=2021 |volume=16 |issue=12 |pages=e0261091 |doi=10.1371/journal.pone.0261091 |pmid=34860855 |pmc=8641874 |doi-access=free|bibcode=2021PLoSO..1661091Z }}</ref>  Most definitions of '''sustainable energy''' include considerations of environmental aspects such as [[greenhouse gas emissions]] and social and economic aspects such as [[energy poverty]]. [[Renewable energy]] sources such as [[wind power|wind]], [[Hydroelectricity|hydroelectric power]], [[solar energy|solar]], and [[geothermal energy]] are generally far more sustainable than fossil fuel sources. However, some renewable energy projects, such as the clearing of forests to produce [[biofuels]], can cause severe environmental damage.

The role of non-renewable energy sources in sustainable energy has been controversial. [[Nuclear power]] is a [[Low-carbon power|low-carbon]] source whose historic mortality rates are comparable to those of wind and solar, but its [[sustainability]] has been debated because of concerns about [[radioactive waste]], [[nuclear proliferation]], and [[Nuclear and radiation accidents and incidents|accidents]]. Switching from coal to natural gas has environmental benefits, including a lower [[climate change|climate impact]], but may lead to a delay in switching to more sustainable options. [[Carbon capture and storage]] can be built into power plants to remove their [[carbon dioxide]] ({{CO2}}) emissions, but this technology is expensive and has rarely been implemented.

[[Fossil fuel]]s provide 85% of the world's energy consumption, and the energy system is responsible for 76% of global greenhouse gas emissions. Around 790&nbsp;million people in [[Developing country|developing countries]] lack [[rural electrification|access to electricity]], and 2.6&nbsp;billion rely on polluting fuels such as wood or charcoal to cook. Reducing greenhouse gas emissions to levels consistent with the 2015 [[Paris Agreement]] will require a system-wide transformation of the way energy is produced, distributed, stored, and consumed. The burning of [[fossil fuels]] and [[biomass]] is a major contributor to [[air pollution]], which causes an estimated 7&nbsp;million deaths each year. Therefore, the transition to a low-carbon energy system would have strong [[Co-benefits of climate change mitigation|co-benefits]] for human health. Pathways exist to provide universal access to electricity and [[clean cooking]] in ways that are compatible with climate goals while bringing major health and economic benefits to developing countries.

[[Climate change mitigation]] pathways have been proposed to limit global warming to {{convert|2|C-change}}. These pathways include phasing out coal-fired power plants, producing more electricity from clean sources such as [[wind energy|wind]] and [[Solar power|solar]], and shifting towards using [[Electrification|electricity instead of fossil fuels]] in sectors such as transport and heating buildings. For some energy-intensive technologies and processes that are difficult to electrify, many pathways describe a growing role for [[Green hydrogen|hydrogen fuel]] produced from low-emission energy sources. To accommodate larger shares of [[variable renewable energy]], [[electrical grid]]s require flexibility through infrastructure such as [[grid energy storage|energy storage]]. To make deep reductions in emissions, infrastructure and technologies that use energy, such as buildings and transport systems, would need to be changed to use clean forms of energy and also [[Energy conservation|conserve energy]]. Some critical technologies for eliminating energy-related greenhouse gas emissions are not yet mature.  

Wind and solar energy generated 8.5% of worldwide electricity in 2019. This share has grown rapidly while costs have fallen and are projected to continue falling. The [[Intergovernmental Panel on Climate Change]] (IPCC) estimates that 2.5% of world [[gross domestic product]] (GDP) would need to be invested in the energy system each year between 2016 and 2035 to limit global warming to {{convert|1.5|C-change}}. Well-designed government policies that promote energy system transformation can lower greenhouse gas emissions and improve air quality. In many cases, they also increase [[energy security]]. Policy approaches include [[Carbon price|carbon pricing]], [[renewable portfolio standard]]s, phase-outs of [[fossil fuel subsidies]], and the development of infrastructure to support electrification and sustainable transport. Funding the research, development, and demonstration of new clean energy technologies is also an important role of the government.

<noinclude>{{Sustainable energy}}</noinclude>

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==Definitions and background==
{{quote box
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| quote = "Energy is the golden thread that connects economic growth, increased social equity, and an environment that allows the world to thrive. Development is not possible without energy, and sustainable development is not possible without sustainable energy."
| author = UN Secretary-General [[Ban Ki-moon]]{{sfn|United Nations Development Programme|2016|p=5}}
| width = 25%
}}

=== Definitions ===
The United Nations [[Brundtland Commission]] described the concept of [[sustainable development]], for which energy is a key component, in its 1987 report ''[[Our Common Future]]''. It defined sustainable development as meeting "the needs of the present without compromising the ability of future generations to meet their own needs".{{Sfn|Kutscher|Milford|Kreith|2019|pp=5–6}} This description of sustainable development has since been referenced in many definitions and explanations of sustainable energy.{{Sfn|Kutscher|Milford|Kreith|2019|pp=5–6}}<ref name=":OU">{{Cite web|publisher=[[The Open University]] |title=Definitions: energy, sustainability and the future |url=https://www.open.edu/openlearn/nature-environment/environmental-studies/introduction-sustainable-energy/content-section-2|access-date=30 December 2020|archive-url=https://web.archive.org/web/20210127144447/https://www.open.edu/openlearn/nature-environment/environmental-studies/introduction-sustainable-energy/content-section-2|archive-date=27 January 2021|url-status=live}}</ref>{{sfn|Golus̆in|Popov|Dodić|2013|p=8}}<ref name=":Galarraga">{{Citec|year=2011 |last1=Hammond|first1=Geoffrey P.|last2=Jones|first2=Craig I.|pages=21–47|in=Galarraga|in2=González-Eguino|in3=Markandya|chapter=Sustainability criteria for energy resources and technologies}}</ref> 

There is no universally accepted interpretation of how the concept of [[sustainability]] applies to energy on a global scale.<ref name=":ECE" /> Working definitions of sustainable energy encompass multiple dimensions of sustainability such as environmental, economic, and social dimensions.<ref name=":Galarraga" /> Historically, the concept of sustainable energy development has focused on emissions and on [[energy security]]. Since the early 1990s, the concept has broadened to encompass wider social and economic issues.<ref>{{Cite journal|last1=Gunnarsdottir|first1=I.|last2=Davidsdottir|first2=B.|last3=Worrel|first3=E. |last4=Sigurgeirsdottir|first4=S.|date=2021|title=Sustainable energy development: History of the concept and emerging themes|url=https://www.sciencedirect.com/science/article/abs/pii/S1364032121000654|journal=[[Renewable and Sustainable Energy Reviews]]|volume=141|pages=110770 |doi=10.1016/j.rser.2021.110770 |s2cid=233585148|issn=1364-0321|access-date=15 August 2021|archive-date=15 August 2021|archive-url=https://web.archive.org/web/20210815092522/https://www.sciencedirect.com/science/article/abs/pii/S1364032121000654|url-status=live}}</ref> 

The environmental dimension of sustainability includes [[Greenhouse gas|greenhouse gas emissions]], impacts on [[biodiversity]] and ecosystems, hazardous waste and toxic emissions,<ref name=":ECE">{{harvnb|UNECE|2020|pp=3–4}}</ref> water consumption,{{Sfn|Kutscher|Milford|Kreith|2019|pp=1–2}} and depletion of non-renewable resources.<ref name=":Galarraga" /> Energy sources with low environmental impact are sometimes called ''green energy'' or ''clean energy''. The economic dimension of sustainability covers economic development, efficient use of energy, and energy security to ensure that each country has constant access to sufficient energy.<ref name=":ECE" /><ref>{{cite journal |last1=Vera |first1=Ivan |last2=Langlois |first2=Lucille |title=Energy indicators for sustainable development |journal=[[Energy (journal)|Energy]] |date=2007 |volume=32 |issue=6 |pages=875–882 |doi=10.1016/j.energy.2006.08.006 |url=https://www.sciencedirect.com/science/article/abs/pii/S0360544206002337 |issn=0360-5442 |access-date=15 August 2021 |archive-date=15 August 2021 |archive-url=https://web.archive.org/web/20210815113307/https://www.sciencedirect.com/science/article/abs/pii/S0360544206002337 |url-status=live }}</ref>{{Sfn|Kutscher|Milford|Kreith|2019|pp=3–5}} Social issues include access to affordable and reliable energy for all people, [[workers rights|workers' rights]], and land rights.<ref name=":Galarraga" /><ref name=":ECE" />

===Environmental impacts===
<!--[[File:Global primary energy consumption, OWID.svg|thumb|upright=1.35|alt=Graph showing growth of energy technologies. Coal shrank slightly between 2014 and 2019, whereas oil and gas grew. Nuclear and hydro had a slow growth, in contrast to other renewables. |The use of modern [[renewable energy]] sources increased from 2000 to 2019 but coal, oil, and natural gas remain the most-used global energy sources.<ref>{{Cite web|title=Global direct primary energy consumption|url=https://ourworldindata.org/grapher/global-primary-energy|access-date=16 July 2021|website=[[Our World in Data]]|archive-date=13 May 2021|archive-url=https://web.archive.org/web/20210513154003/https://ourworldindata.org/grapher/global-primary-energy|url-status=live}}</ref>]]-->
[[File:Rajasthan carrying firewood.jpeg|thumb|alt=Photograph of a woman carrying firewood she has gathered on her head| A woman in rural [[Rajasthan]], India, collects firewood. The [[Energy poverty and cooking|use of wood and other polluting fuels for cooking]] causes millions of deaths each year from [[Indoor air pollution in developing nations|indoor]] and outdoor [[air pollution]].]]
The current energy system contributes to many environmental problems, including [[climate change]], [[air pollution]], [[biodiversity loss]], the release of toxins into the environment, and water scarcity. As of 2019, 85% of the world's energy needs are met by burning fossil fuels.{{sfn|United Nations Environment Programme|2019|p=46}} Energy production and consumption are responsible for 76% of annual human-caused greenhouse gas emissions as of 2018.<ref name=":23">{{Cite web|title=Global Historical Emissions |url=https://www.climatewatchdata.org/ghg-emissions?breakBy=sector&chartType=percentage&end_year=2018&sectors=total-including-lucf&start_year=1990 |access-date=19 August 2021 |website=[[Climate Watch (World Resources Institute)|Climate Watch]]|archive-date=4 June 2021|archive-url=https://web.archive.org/web/20210604144234/https://www.climatewatchdata.org/ghg-emissions?breakBy=sector&chartType=percentage&end_year=2018&start_year=1990|url-status=live}}</ref><ref>{{cite news |last1=Ge |first1=Mengpin |last2=Friedrich |first2=Johannes |last3=Vigna |first3=Leandro |title=4 Charts Explain Greenhouse Gas Emissions by Countries and Sectors |url=https://www.wri.org/insights/4-charts-explain-greenhouse-gas-emissions-countries-and-sectors |access-date=19 August 2021 |date=August 2021 |publisher=[[World Resources Institute]] |archive-date=19 August 2021 |archive-url=https://web.archive.org/web/20210819011608/https://www.wri.org/insights/4-charts-explain-greenhouse-gas-emissions-countries-and-sectors |url-status=live }}</ref> The 2015 international [[Paris Agreement]] on climate change aims to limit global warming to well below {{convert|2|C-change}} and preferably to 1.5&nbsp;°C (2.7&nbsp;°F); achieving this goal will require that emissions be reduced as soon as possible and reach [[Net-zero emissions|net-zero]] by mid-century.<ref>{{Cite web|publisher=[[United Nations Framework Convention on Climate Change]]|title=The Paris Agreement|url=https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement|url-status=live|access-date=18 September 2021|archive-date=19 March 2021|archive-url=https://web.archive.org/web/20210319205057/https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement}}</ref>

The burning of fossil fuels and [[biomass]] is a major source of [[air pollution]],<ref>{{cite journal |last1=Watts|first1=Nick|last2=Amann|first2=Markus|last3=Arnell|first3=Nigel|last4=Ayeb-Karlsson |first4=Sonja|last5=Beagley |first5=Jessica|last6=Belesova|first6=Kristine|last7=Boykoff|first7=Maxwell |last8=Byass|first8=Peter|last9=Cai|first9=Wenjia|last10=Campbell-Lendrum|first10=Diarmid|display-authors=4 |date=2021|title=The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises|journal=[[The Lancet]]|volume=397|issue=10269|page=151|doi=10.1016/S0140-6736(20)32290-X |pmid=33278353|issn=0140-6736|doi-access=free|url=http://gala.gre.ac.uk/id/eprint/33779/1/33779_DOMINGUEZ%20SALAS_2020_report_of_the_Lancet_countdown.pdf}}</ref><ref>{{Cite web |publisher=[[United Nations Development Programme]]|date=4 June 2019|title=Every breath you take: The staggering, true cost of air pollution|url=https://stories.undp.org/every-breath-you-take|url-status=live|access-date=4 May 2021 |archive-url=https://web.archive.org/web/20210420022524/https://stories.undp.org/every-breath-you-take |archive-date=20 April 2021}}</ref> which causes an estimated 7&nbsp;million deaths each year, with the greatest attributable disease burden seen in low and middle-income countries.<ref>{{Cite web|date=22 September 2021|title=New WHO Global Air Quality Guidelines aim to save millions of lives from air pollution|url=https://www.who.int/news/item/22-09-2021-new-who-global-air-quality-guidelines-aim-to-save-millions-of-lives-from-air-pollution |url-status=live|access-date=16 October 2021|publisher=[[World Health Organization]]|archive-date=23 September 2021|archive-url=https://web.archive.org/web/20210923021545/https://www.who.int/news/item/22-09-2021-new-who-global-air-quality-guidelines-aim-to-save-millions-of-lives-from-air-pollution}}</ref> Fossil-fuel burning in power plants, vehicles, and factories is the main source of emissions that combine with oxygen in the atmosphere to cause [[acid rain]].<ref>{{Cite web|publisher=[[United States Geological Survey]]|title=Acid Rain and Water|url=https://www.usgs.gov/special-topic/water-science-school/science/acid-rain-and-water?qt-science_center_objects=0#qt-science_center_objects|url-status=live|access-date=14 October 2021|archive-date=27 June 2021|archive-url=https://web.archive.org/web/20210627103228/https://www.usgs.gov/special-topic/water-science-school/science/acid-rain-and-water?qt-science_center_objects=0#qt-science_center_objects}}</ref> Air pollution is the second-leading cause of death from non-infectious disease.{{sfn|World Health Organization|2018|p=16}} An estimated 99% of the world's population lives with levels of air pollution that exceed the [[World Health Organization]] recommended limits.<ref>{{Cite web|date=22 September 2021 |title=Ambient (outdoor) air pollution|url=https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health|access-date=22 October 2021|publisher=[[World Health Organization]]|url-status=live|archive-url=https://web.archive.org/web/20211008055940/https://www.who.int/news-room/fact-sheets/detail/ambient-%28outdoor%29-air-quality-and-health|archive-date=8 October 2021}}</ref> 

[[Energy poverty and cooking|Cooking with polluting fuels]] such as wood, animal dung, coal, or [[kerosene]] is responsible for nearly all indoor air pollution, which causes an estimated 1.6 to 3.8&nbsp;million deaths annually,<ref>{{cite journal|last1=Ritchie|first1=Hannah|last2=Roser|first2=Max |date=2019|title=Access to Energy|url=https://ourworldindata.org/indoor-air-pollution#indoor-air-pollution-is-one-of-the-leading-risk-factors-for-premature-death|access-date=1 April 2021|url-status=live|archive-url=https://web.archive.org/web/20210401122036/https://ourworldindata.org/indoor-air-pollution#indoor-air-pollution-is-one-of-the-leading-risk-factors-for-premature-death |archive-date=1 April 2021 |journal=[[Our World in Data]]}}</ref>{{sfn|World Health Organization|2018|p=16}} and also contributes significantly to outdoor air pollution.{{sfn|World Health Organization|2016|pp=vii–xiv}} Health effects are concentrated among women, who are likely to be responsible for cooking, and young children.{{sfn|World Health Organization|2016|pp=vii–xiv}}

Environmental impacts extend beyond the by-products of combustion. [[Oil spill]]s at sea harm marine life and may cause fires which release toxic emissions.{{sfn|Soysal|Soysal|2020|p=118}} Around 10% of global water use goes to energy production, mainly for cooling in thermal energy plants. In dry regions, this contributes to [[water scarcity]]. Bioenergy production, coal mining and processing, and oil extraction also require large amounts of water.{{sfn|Soysal|Soysal|2020|pp=470–472}} Excessive harvesting of wood and other combustible material for burning can cause serious local environmental damage, including [[desertification]].{{sfn|Tester|2012|p=504}}

In 2021, [[UNECE]] published a lifecycle analysis of the environmental impact of numerous electricity generation technologies, accounting for the following: resource use (minerals, metals); land use; resource use (fossils); water use; particulate matter; photochemical ozone formation; ozone depletion; human toxicity (non-cancer); ionising radiation; human toxicity (cancer); eutrophication (terrestrial, marine, freshwater); ecotoxicity (freshwater); acidification; climate change.<ref name=":9">{{Cite report|title=Life Cycle Assessment of Electricity Generation Options|publisher=[[United Nations Economic Commission for Europe]]|url=https://unece.org/sed/documents/2021/10/reports/life-cycle-assessment-electricity-generation-options|access-date=24 November 2021|page=59|date=|archive-date=15 November 2021|archive-url=https://web.archive.org/web/20211115074531/https://unece.org/sed/documents/2021/10/reports/life-cycle-assessment-electricity-generation-options|url-status=live}}</ref>

=== Sustainable development goals ===
{{Further|Energy poverty|Energy poverty and cooking}}
[[File:People-without-electricity-country-2016.svg|thumb|upright=1.35|alt=Map of people with access to energy. Lack of access is most pronounced in India, Sub-Saharan Africa and South-East Asia.|World map showing where people without access to electricity lived in 2016⁠—mainly in [[sub-Saharan Africa]] and the [[Indian subcontinent]]]]
Meeting existing and future energy demands in a sustainable way is a critical challenge for the global goal of limiting climate change while maintaining economic growth and enabling living standards to rise.<ref>{{Cite web |last1=Kessides|first1=Ioannis N.|last2=Toman|first2=Michael|date=28 July 2011|title=The Global Energy Challenge|url=https://blogs.worldbank.org/developmenttalk/the-global-energy-challenge|archive-url=https://web.archive.org/web/20190725174744/http://blogs.worldbank.org/developmenttalk/the-global-energy-challenge|archive-date=25 July 2019|access-date=27 September 2019|url-status=live|publisher=[[World Bank]]}}</ref> Reliable and affordable energy, particularly electricity, is essential for health care, education, and economic development.{{sfn|Morris|Mensah-Kutin|Greene|Diam-valla|2015|pp=24–27}} As of 2020, 790&nbsp;million people in developing countries do not have access to electricity, and around 2.6&nbsp;billion rely on burning polluting fuels for cooking.<ref name=":3">{{Cite web|date=October 2020 |title=Access to clean cooking|work=SDG7: Data and Projections |url=https://www.iea.org/reports/sdg7-data-and-projections/access-to-clean-cooking|access-date=31 March 2021|url-status=live|archive-url=https://web.archive.org/web/20191206163046/https://www.iea.org/reports/sdg7-data-and-projections/access-to-clean-cooking|archive-date=6 December 2019|publisher=[[International Energy Agency|IEA]]|ref=none}}</ref>{{sfn|IEA|2021|p=167}} 

Improving energy access in the [[Least developed countries|least-developed countries]] and making energy cleaner are key to achieving most of the United Nations 2030 [[Sustainable Development Goals]],<ref>{{Cite journal |last=Sarkodie |first=Samuel Asumadu |date=20 July 2022 |title=Winners and losers of energy sustainability—Global assessment of the Sustainable Development Goals |journal=Science of the Total Environment |volume=831 |at=154945 |doi=10.1016/j.scitotenv.2022.154945 |pmid=35367559 |bibcode=2022ScTEn.831o4945S |s2cid=247881708 |issn=0048-9697 |doi-access=free |hdl=11250/3023660 |hdl-access=free }}</ref> which cover issues ranging from [[Sustainable Development Goal 14|climate action]] to [[Sustainable Development Goal 5|gender equality]].<ref name="Welcome to the United Nations 2018">{{cite press release|author=Deputy Secretary-General|date=6 June 2018|title=Sustainable Development Goal 7 on Reliable, Modern Energy 'Golden Thread' Linking All Other Targets, Deputy-Secretary-General Tells High-Level Panel|publisher=[[United Nations]] |url=https://www.un.org/press/en/2018/dsgsm1182.doc.htm|url-status=live|access-date=19 March 2021|archive-url=https://web.archive.org/web/20210517215032/https://www.un.org/press/en/2018/dsgsm1182.doc.htm|archive-date=17 May 2021}}</ref> [[Sustainable Development Goal 7]] calls for "access to affordable, reliable, sustainable and modern energy for all", including universal [[access to electricity]] and to [[Clean cooking|clean cooking facilities]] by 2030.<ref name=":5">{{Cite web|title=Goal 7: Ensure access to affordable, reliable, sustainable and modern energy for all|url=https://sdg-tracker.org/energy|work=SDG Tracker |archive-url=https://web.archive.org/web/20210202044832/https://sdg-tracker.org/energy|archive-date=2 February 2021|access-date=12 March 2021|url-status=live}}</ref>

==Energy conservation==
{{Main|Energy conservation|Efficient energy use}}
[[File:Energy use per person 2019 - OWID.svg|thumb|upright=1.35|alt=Countries such as the US and Canada use twice as much energy per capita as Japan or western Europe, and 100 times as much commercial energy per capita as some African countries.|[[World energy consumption|Global energy usage]] is highly unequal. High income countries such as the United States and Canada use 100 times as much energy per capita as some of the [[least developed countries]] in Africa.<ref>{{Cite web|title=Energy use per person|website=[[Our World in Data]] |url=https://ourworldindata.org/grapher/per-capita-energy-use|access-date=16 July 2021|archive-url=https://web.archive.org/web/20201128155350/https://ourworldindata.org/grapher/per-capita-energy-use |archive-date=28 November 2020|url-status=live}}</ref>]]
Energy efficiency—using less energy to deliver the same goods or services, or delivering comparable services with less goods—is a cornerstone of many sustainable energy strategies.<ref>{{Cite web|date=25 February 2016|title=Europe 2030: Energy saving to become "first fuel" |url=https://ec.europa.eu/jrc/en/news/europe-2030-energy-saving-become-first-fuel|url-status=live|access-date=18 September 2021|work=EU Science Hub|publisher=[[European Commission]]|archive-date=18 September 2021|archive-url=https://web.archive.org/web/20210918213742/https://ec.europa.eu/jrc/en/news/europe-2030-energy-saving-become-first-fuel}}</ref><ref>{{Cite web|last=Motherway|first=Brian|date=19 December 2019|title=Energy efficiency is the first fuel, and demand for it needs to grow|url=https://www.iea.org/commentaries/energy-efficiency-is-the-first-fuel-and-demand-for-it-needs-to-grow|url-status=live|access-date=18 September 2021|publisher=[[International Energy Agency|IEA]]|archive-date=18 September 2021|archive-url=https://web.archive.org/web/20210918213716/https://www.iea.org/commentaries/energy-efficiency-is-the-first-fuel-and-demand-for-it-needs-to-grow}}</ref> The [[International Energy Agency]] (IEA) has estimated that increasing energy efficiency could achieve 40% of greenhouse gas emission reductions needed to fulfil the Paris Agreement's goals.<ref>{{Cite web| date=October 2018 |title=Energy Efficiency 2018: Analysis and outlooks to 2040|url=https://www.iea.org/reports/energy-efficiency-2018|url-status=live|publisher=[[International Energy Agency|IEA]]|archive-date=29 September 2020|archive-url=https://web.archive.org/web/20200929142015/https://www.iea.org/reports/energy-efficiency-2018}}</ref>   

Energy can be conserved by increasing the technical efficiency of appliances, vehicles, industrial processes, and buildings.<ref>{{Cite web|date=10 June 2021|title=Net zero by 2050 hinges on a global push to increase energy efficiency|url=https://www.iea.org/articles/net-zero-by-2050-hinges-on-a-global-push-to-increase-energy-efficiency|url-status=live|access-date=19 July 2021|publisher=[[International Energy Agency|IEA]]|last1=Fernandez Pales |first1=Araceli|first2=Stéphanie|last2=Bouckaert|first3=Thibaut |last3=Abergel|first4=Timothy|last4=Goodson|archive-date=20 July 2021|archive-url=https://web.archive.org/web/20210720145913/https://www.iea.org/articles/net-zero-by-2050-hinges-on-a-global-push-to-increase-energy-efficiency}}</ref> Another approach is to use fewer materials whose production requires a lot of energy, for example through better building design and recycling. Behavioural changes such as using [[videoconferencing]] rather than business flights, or making urban trips by cycling, walking or public transport rather than by car, are another way to conserve energy.{{sfn|IEA|2021|pp=68–69}} Government policies to improve efficiency can include [[building codes]], [[Minimum energy performance standard|performance standards]], [[Carbon price|carbon pricing]], and the development of energy-efficient infrastructure to encourage [[modal shift|changes in transport modes]].{{sfn|IEA|2021|pp=68–69}}<ref>{{Cite journal|last1=Mundaca|first1=Luis|last2=Ürge-Vorsatz|first2=Diana|author-link2=Diana Ürge-Vorsatz |last3=Wilson|first3=Charlie|date=2019|title=Demand-side approaches for limiting global warming to 1.5&nbsp;°C|url=https://lup.lub.lu.se/search/files/49859700/Energy_Efficiency3.pdf|journal=[[Energy Efficiency (journal)|Energy Efficiency]] |volume=12|issue=2|pages=343–362 |doi=10.1007/s12053-018-9722-9|issn=1570-6478|doi-access=free|s2cid=52251308}}</ref>

The [[energy intensity]] of the global economy (the amount of energy consumed per unit of [[gross domestic product]] (GDP)) is a rough indicator of the energy efficiency of economic production.{{Sfn|IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization|2021|p=12}} In 2010, global energy intensity was 5.6 megajoules (1.6 [[Kilowatt-hour|kWh]]) per US dollar of GDP.{{Sfn|IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization|2021|p=12}} United Nations goals call for energy intensity to decrease by 2.6% each year between 2010 and 2030.{{Sfn|IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization|2021|p=11}} In recent years this target has not been met. For instance, between 2017 and 2018, energy intensity decreased by only 1.1%.{{Sfn|IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization|2021|p=11}} Efficiency improvements often lead to a [[Jevons paradox|rebound effect]] in which consumers use the money they save to buy more energy-intensive goods and services.<ref>{{Cite journal|last1=Brockway |first1=Paul |last2=Sorrell|first2=Steve|last3=Semieniuk|first3=Gregor|last4=Heun|first4=Matthew K.|last5=Court |first5=Victor|date=2021|display-authors=4|title=Energy efficiency and economy-wide rebound effects: A review of the evidence and its implications|journal=[[Renewable and Sustainable Energy Reviews]]|volume=141 |pages=110781|issn=1364-0321 |doi=10.1016/j.rser.2021.110781|s2cid=233554220|doi-access=free|url=https://eprints.whiterose.ac.uk/171952/1/brockway%20sorrell%20et%20al%202021%20large%20rebound%20paper_2.pdf}}</ref> For example, recent technical efficiency improvements in transport and buildings have been largely offset by trends in [[consumer behaviour]], such as [[Autobesity|selecting larger vehicles]] and homes.<ref name=":6">{{Cite web |date=November 2019|title=Energy Efficiency 2019 |url=https://www.iea.org/reports/energy-efficiency-2019|url-status=live|archive-url=https://web.archive.org/web/20201013050500/https://www.iea.org/reports/energy-efficiency-2019 |archive-date=13 October 2020|access-date=21 September 2020|publisher=[[International Energy Agency|IEA]]}}</ref>

==Sustainable energy sources==
===Renewable energy sources===
{{Main|Renewable energy}}
{{ multiple image | align = right | total_width =450
| image1= 2010- Fossil fuels vs Wind + Solar - electricity generation.svg |caption1=In 2023, electricity generation from wind and solar sources was projected to exceed 30% by 2030.<ref name=RMI_20230613>{{cite web |last1=Bond |first1=Kingsmill |last2=Butler-Sloss |first2=Sam |last3=Lovins |first3=Amory |last4=Speelman |first4=Laurens |last5=Topping |first5=Nigel |title=Report / 2023 / X-Change: Electricity / On track for disruption |publisher=Rocky Mountain Institute |url=https://rmi.org/insight/x-change-electricity/ |archive-url=https://web.archive.org/web/20230713171138/https://rmi.org/insight/x-change-electricity/ |archive-date=13 July 2023 |date=13 June 2023 |url-status=live }}</ref>
| image2=2011- Renewable energy capacity - International Energy Agency.svg| |alt=Graph showing the expansion of wind and solar renewable energy capacity from 2011 to 2020 |caption2=Renewable energy capacity has steadily grown, led by [[Photovoltaic system|solar photovoltaic]] power.<ref name=IEA_202306>Source for data beginning in 2017: {{cite web |title=Renewable Energy Market Update Outlook for 2023 and 2024 |url=https://iea.blob.core.windows.net/assets/63c14514-6833-4cd8-ac53-f9918c2e4cd9/RenewableEnergyMarketUpdate_June2023.pdf |website=IEA.org |publisher=International Energy Agency (IEA) |archive-url=https://web.archive.org/web/20230711115355/https://iea.blob.core.windows.net/assets/63c14514-6833-4cd8-ac53-f9918c2e4cd9/RenewableEnergyMarketUpdate_June2023.pdf |archive-date=11 July 2023 |page=19 |date=June 2023 |quote=IEA. CC BY 4.0. |url-status=live}} ● Source for data through 2016: {{cite web |title=Renewable Energy Market Update / Outlook for 2021 and 2022 |url=https://iea.blob.core.windows.net/assets/18a6041d-bf13-4667-a4c2-8fc008974008/RenewableEnergyMarketUpdate-Outlookfor2021and2022.pdf |website=IEA.org |publisher=International Energy Agency |archive-url=https://web.archive.org/web/20230325084025/https://iea.blob.core.windows.net/assets/18a6041d-bf13-4667-a4c2-8fc008974008/RenewableEnergyMarketUpdate-Outlookfor2021and2022.pdf |archive-date=25 March 2023 |page=8 |date=May 2021 |url-status=live |quote=IEA. Licence: CC BY 4.0 }}</ref>
}}
[[File:2015- Clean energy vs fossil fuel investment - IEA.svg |thumb |Clean energy investment has benefited from post-pandemic economic recovery, a global energy crisis involving high fossil fuel prices, and growing policy support across various nations.<ref name=IEA_20230525>{{cite web |title=World Energy Investment 2023 / Overview and key findings |url=https://www.iea.org/reports/world-energy-investment-2023/overview-and-key-findings |publisher=International Energy Agency (IEA) |archive-url=https://web.archive.org/web/20230531004551/https://www.iea.org/reports/world-energy-investment-2023/overview-and-key-findings |archive-date=31 May 2023 |date=25 May 2023 |quote=Global energy investment in clean energy and in fossil fuels, 2015-2023 (chart) |url-status=live}} — From pages 8 and 12 of [https://iea.blob.core.windows.net/assets/8834d3af-af60-4df0-9643-72e2684f7221/WorldEnergyInvestment2023.pdf ''World Energy Investment 2023''] ([https://web.archive.org/web/20230531003621/https://iea.blob.core.windows.net/assets/8834d3af-af60-4df0-9643-72e2684f7221/WorldEnergyInvestment2023.pdf archive]).</ref>]]
Renewable energy sources are essential to sustainable energy, as they generally strengthen energy security and emit far fewer greenhouse gases than [[fossil fuel]]s.{{sfn|IEA|2007|p=3}} Renewable energy projects sometimes raise significant sustainability concerns, such as risks to biodiversity when areas of high ecological value are converted to bioenergy production or wind or solar farms.<ref>{{cite journal |last1=Santangeli|first1=Andrea|last2=Toivonen|first2=Tuuli|last3=Pouzols|first3=Federico Montesino |last4=Pogson|first4=Mark|last5=Hastings|first5=Astley|last6=Smith|first6=Pete|last7=Moilanen|first7=Atte |display-authors=4 |date=2016|title=Global change synergies and trade-offs between renewable energy and biodiversity|journal=[[GCB Bioenergy]]|volume=8|issue=5|pages=941–951|doi=10.1111/gcbb.12299|issn=1757-1707|doi-access=free|bibcode=2016GCBBi...8..941S |hdl=2164/6138|hdl-access=free}}</ref><ref>{{cite journal|last1=Rehbein|first1=Jose A.|last2=Watson|first2=James E.M. |last3=Lane|first3=Joe L.|last4=Sonter|first4=Laura J.|last5=Venter|first5=Oscar|last6=Atkinson |first6=Scott C.|last7=Allan|first7=James R.|display-authors=4 |date=2020|title=Renewable energy development threatens many globally important biodiversity areas|journal=[[Global Change Biology]] |volume=26|issue=5|pages=3040–3051|doi=10.1111/gcb.15067|pmid=32133726|bibcode=2020GCBio..26.3040R |s2cid=212418220|issn=1365-2486|url=https://espace.library.uq.edu.au/view/UQ:902f5a3/UQ902f5a3_OA.pdf}}</ref>

Hydropower is the largest source of renewable electricity while solar and wind energy are growing rapidly. [[Photovoltaic system|Photovoltaic solar]] and [[Wind power|onshore wind]] are the cheapest forms of new power generation capacity in most countries.<ref>{{cite web |date=2019 |last1=Ritchie |first1=Hannah |author1-link=Hannah Ritchie |title=Renewable Energy |website=[[Our World in Data]] |url=https://ourworldindata.org/renewable-energy |access-date=31 July 2020 |url-status=live |archive-date=4 August 2020 |archive-url=https://web.archive.org/web/20200804120952/https://ourworldindata.org/renewable-energy}}</ref><ref name="IEA Renewables 2020">{{cite report |publisher=[[International Energy Agency|IEA]] |year=2020 |ref=none| title=Renewables 2020 Analysis and forecast to 2025 |url=https://iea.blob.core.windows.net/assets/1a24f1fe-c971-4c25-964a-57d0f31eb97b/Renewables_2020-PDF.pdf |url-status=live |page=12 |archive-date=26 April 2021 |archive-url=https://web.archive.org/web/20210426063553/https://www.iea.org/reports/renewables-2020}}</ref> For more than half of the 770&nbsp;million people who currently lack access to electricity, [[Distributed generation|decentralised renewable energy]] such as solar-powered mini-grids is likely the cheapest method of providing it by 2030.<ref name=":1">{{Cite web|date=2020|ref=none|title=Access to electricity|work=SDG7: Data and Projections|url=https://www.iea.org/reports/sdg7-data-and-projections/access-to-electricity|url-status=live|archive-url=https://web.archive.org/web/20210513103128/https://www.iea.org/reports/sdg7-data-and-projections/access-to-electricity|archive-date=13 May 2021|access-date=5 May 2021|publisher=[[International Energy Agency|IEA]]}}</ref> United Nations targets for 2030 include substantially increasing the proportion of renewable energy in the world's energy supply.<ref name=":5" /> According to the International Energy Agency, renewable energy sources like wind and solar power are now a commonplace source of electricity, making up 70% of all new investments made in the world's power generation.<ref name=":732">{{Cite web |title=Infrastructure Solutions: The power of purchase agreements |url=https://www.eib.org/en/essays/renewable-energy-power-purchase-agreements |access-date=1 September 2022 |website=European Investment Bank |language=en}}</ref><ref>{{Cite web |title=Renewable Power – Analysis |url=https://www.iea.org/reports/renewable-power |access-date=1 September 2022 |website=IEA |language=en-GB}}</ref><ref>{{Cite web |date=29 March 2022 |title=Global Electricity Review 2022 |url=https://ember-climate.org/insights/research/global-electricity-review-2022/ |access-date=1 September 2022 |website=Ember |language=en-US}}</ref><ref>{{Cite web |title=Renewable Energy and Electricity {{!}} Sustainable Energy {{!}} Renewable Energy - World Nuclear Association |url=https://world-nuclear.org/information-library/energy-and-the-environment/renewable-energy-and-electricity.aspx |access-date=1 September 2022 |website=world-nuclear.org}}</ref> The Agency expects renewables to become the primary energy source for electricity generation globally in the next three years, overtaking coal.<ref name=":24">IEA (2022), Renewables 2022, IEA, Paris https://www.iea.org/reports/renewables-2022, License: CC BY 4.0</ref>

====Solar====
[[File:Renewable Energy Development in the California Desert 006.jpg|thumb|A [[photovoltaic power station]] in [[California]], United States|alt=long rows of dark panels, sloped about 45 degrees at the height of a person, stretch into the distance in bright sunshine]]
{{main|Solar power|Solar water heating}}
The Sun is Earth's primary source of energy, a clean and abundantly available resource in many regions.{{sfn|Soysal|Soysal|2020|p=406}} In 2019, solar power provided around 3% of global electricity,<ref name=":4">{{Cite web |title=Wind & Solar Share in Electricity Production Data|publisher=[[Enerdata]] |url=https://yearbook.enerdata.net/renewables/wind-solar-share-electricity-production.html|work=Global Energy Statistical Yearbook 2021|access-date=13 June 2021|archive-date=19 July 2019|archive-url=https://web.archive.org/web/20190719014426/https://yearbook.enerdata.net/renewables/wind-solar-share-electricity-production.html|url-status=live}}</ref> mostly through [[solar panels]] based on [[photovoltaic cells]] (PV). Solar PV is expected to be the electricity source with the largest installed capacity worldwide by 2027.<ref name=":24" /> The panels are mounted on top of buildings or installed in utility-scale [[photovoltaic power station|solar parks]]. Costs of solar photovoltaic cells have dropped rapidly, driving strong growth in worldwide capacity.{{Sfn|Kutscher|Milford|Kreith|2019|p=|pp=34–35}} The [[Cost of electricity by source|cost of electricity]] from new solar farms is competitive with, or in many places, cheaper than electricity from existing coal plants.<ref name=":10">{{Cite web|date=19 October 2020|title=Levelized Cost of Energy and of Storage|url=http://www.lazard.com/perspective/levelized-cost-of-energy-and-levelized-cost-of-storage-2020/|url-status=live|access-date=26 February 2021|publisher=[[Lazard]]|archive-date=25 February 2021 |archive-url=https://web.archive.org/web/20210225114950/https://www.lazard.com/perspective/levelized-cost-of-energy-and-levelized-cost-of-storage-2020/}}</ref> Various projections of future energy use identify solar PV as one of the main sources of energy generation in a sustainable mix.<ref>{{Cite journal|date=2021 |title=Solar photovoltaics is ready to power a sustainable future|journal=[[Joule (journal)|Joule]] |volume=5|issue=5|pages=1041–1056|doi=10.1016/j.joule.2021.03.005|first1=Marta|last1=Victoria|first2=Nancy |last2=Haegel|author2-link=Nancy Haegel|first3=Ian Marius|last3=Peters |first4=Ron|last4=Sinton|osti=1781630 |display-authors=etal|issn=2542-4351|doi-access=free}}</ref>{{sfn|IRENA|2021|pp=19, 22}}

Most components of solar panels can be easily recycled, but this is not always done in the absence of regulation.<ref>{{Cite journal|last1=Goetz|first1=Katelyn P.|last2=Taylor|first2=Alexander D. |last3=Hofstetter|first3=Yvonne J. |last4=Vaynzof|first4=Yana|date=2020|title=Sustainability in Perovskite Solar Cells|url=https://pubs.acs.org/doi/full/10.1021/acsami.0c17269|journal=[[ACS Applied Materials & Interfaces]]|volume=13|issue=1|pages=1–17 |doi=10.1021/acsami.0c17269|pmid=33372760|s2cid=229714294 |issn=1944-8244}}</ref> Panels typically contain [[heavy metals]], so they pose environmental risks if put in [[landfill]]s.<ref>{{Cite journal|last1=Xu|first1=Yan|last2=Li |first2=Jinhui|last3=Tan|first3=Quanyin |last4=Peters|first4=Anesia Lauren|display-authors=etal|date=2018|title=Global status of recycling waste solar panels: A review|journal=[[Waste Management (journal)|Waste Management]] |volume=75|pages=450–458 |url=https://www.sciencedirect.com/science/article/abs/pii/S0956053X18300576|access-date=28 June 2021 |doi=10.1016/j.wasman.2018.01.036|pmid=29472153|bibcode=2018WaMan..75..450X |issn=0956-053X |archive-date=28 June 2021|archive-url=https://web.archive.org/web/20210628193335/https://www.sciencedirect.com/science/article/abs/pii/S0956053X18300576|url-status=live}}</ref> It takes fewer than two years for a solar panel to produce as much energy as was used for its production. Less energy is needed if materials are recycled rather than mined.<ref>{{Cite journal|last1=Tian|first1=Xueyu|last2=Stranks|first2=Samuel D.|last3=You|first3=Fengqi |date=2020|title=Life cycle energy use and environmental implications of high-performance perovskite tandem solar cells|journal=[[Science Advances]]|volume=6|issue=31|pages=eabb0055 |doi=10.1126/sciadv.abb0055|pmc=7399695|issn=2375-2548|pmid=32937582|bibcode=2020SciA....6...55T|s2cid=220937730}}</ref>

In [[concentrated solar power]], solar rays are concentrated by a field of mirrors, heating a fluid. Electricity is produced from the resulting steam with a [[heat engine]]. Concentrated solar power can support [[Dispatchable generation|dispatchable power generation]], as some of the heat is typically stored to enable electricity to be generated when needed.{{Sfn|Kutscher|Milford|Kreith|2019|pp=35–36}}<ref>{{Cite web|title=Solar energy|publisher=[[International Renewable Energy Agency]]|url=https://www.irena.org/solar |access-date=5 June 2021|archive-url=https://web.archive.org/web/20210513154426/https://www.irena.org/solar |archive-date=13 May 2021|url-status=live}}</ref> In addition to electricity production, solar energy is used more directly; [[Solar thermal energy|solar thermal heating]] systems are used for hot water production, heating buildings, drying, and desalination.{{sfn|REN21|2020|p=124}}

====Wind power====
{{main|Wind power|Environmental impact of wind power}}
[[File:Wind_power_plants_in_Xinjiang,_China.jpg|thumb|Wind turbines in [[Xinjiang]], China|alt=Photograph of wind turbines against a hazy orange sky]]
Wind has been an important driver of development over millennia, providing mechanical energy for industrial processes, water pumps, and sailing ships.{{Sfn|Soysal|Soysal|2020|p=366}} Modern wind turbines are used to generate electricity and provided approximately 6% of global electricity in 2019.<ref name=":4" /> Electricity from onshore [[wind farms]] is often cheaper than existing coal plants and competitive with natural gas and nuclear.<ref name=":10" /> Wind turbines can also be placed offshore, where winds are steadier and stronger than on land but construction and maintenance costs are higher.<ref>{{Cite web|date=12 May 2016|title=What are the advantages and disadvantages of offshore wind farms?|url=https://www.americangeosciences.org/critical-issues/faq/what-are-advantages-and-disadvantages-offshore-wind-farms|access-date=18 September 2021|publisher=[[American Geosciences Institute]] |archive-date=18 September 2021|archive-url=https://web.archive.org/web/20210918215856/https://www.americangeosciences.org/critical-issues/faq/what-are-advantages-and-disadvantages-offshore-wind-farms|url-status=live}}</ref> 

Onshore wind farms, often built in wild or rural areas, have a visual impact on the landscape.{{sfn|Szarka|2007|p=176}} While collisions with wind turbines kill both [[bat]]s and to a lesser extent birds, these impacts are lower than from other infrastructure such as windows and [[Overhead power line|transmission lines]].<ref>{{Cite journal|last1=Wang|first1=Shifeng|last2=Wang|first2=Sicong|date=2015 |title=Impacts of wind energy on environment: A review |journal=[[Renewable and Sustainable Energy Reviews]]|volume=49|pages=437–443|doi=10.1016/j.rser.2015.04.137|issn=1364-0321 |url=https://www.sciencedirect.com/science/article/abs/pii/S1364032115004074|access-date=15 June 2021 |archive-date=4 June 2021|archive-url=https://web.archive.org/web/20210604062326/https://www.sciencedirect.com/science/article/abs/pii/S1364032115004074|url-status=live}}</ref>{{Sfn|Soysal|Soysal|2020|p=215}} The noise and flickering light created by the turbines can cause annoyance and constrain construction near densely populated areas. Wind power, in contrast to nuclear and fossil fuel plants, does not consume water.{{Sfn|Soysal|Soysal|2020|p=213}} Little energy is needed for wind turbine construction compared to the energy produced by the wind power plant itself.<ref>{{Cite journal|last1=Huang|first1=Yu-Fong|last2=Gan|first2=Xing-Jia |last3=Chiueh|first3=Pei-Te |date=2017|title=Life cycle assessment and net energy analysis of offshore wind power systems |url=https://www.sciencedirect.com/science/article/pii/S0960148116309156|journal=[[Renewable Energy (journal)|Renewable Energy]]|volume=102|pages=98–106|doi=10.1016/j.renene.2016.10.050|issn=0960-1481}}</ref> Turbine blades are not fully recyclable, and research into methods of manufacturing easier-to-recycle blades is ongoing.<ref>{{Cite news|last=Belton|first=Padraig|date=7 February 2020|title=What happens to all the old wind turbines?|publisher=[[BBC]]|url=https://www.bbc.com/news/business-51325101|url-status=live|access-date=27 February 2021|archive-date=23 February 2021|archive-url=https://web.archive.org/web/20210223042808/https://www.bbc.com/news/business-51325101}}</ref>

====Hydropower====
{{Main|Hydroelectricity}}
[[File:Central Hidroeléctrica Simón Bolívar Represa de Guri Гідроелектростанція Симона Болівара - гребля Гурі 29.jpg|thumb|alt=a river flows smoothly from rectangular openings at the base of a high sloping concrete wall, with electricity wires above the river|[[Guri Dam]], a hydroelectric dam in [[Venezuela]]]]
[[Hydroelectricity|Hydroelectric plants]] convert the energy of moving water into electricity. In 2020, hydropower supplied 17% of the world's electricity, down from a high of nearly 20% in the mid-to-late 20th century.{{sfn|Smil|2017b|p=286}}{{sfn|REN21|2021|p=21}} 

In conventional hydropower, a reservoir is created behind a dam. Conventional hydropower plants provide a highly flexible, [[Dispatchable generation|dispatchable]] electricity supply. They can be combined with wind and solar power to meet peaks in demand and to compensate when wind and sun are less available.<ref name=":15" />

Compared to reservoir-based facilities, [[run-of-the-river hydroelectricity]] generally has less environmental impact. However, its ability to generate power depends on river flow, which can vary with daily and seasonal weather. Reservoirs provide water quantity controls that are used for flood control and flexible electricity output while also providing security during drought for drinking water supply and irrigation.<ref>{{citec |last1=Kumar |first1=A.|first2=T.|last2=Schei|first3=A.|last3=Ahenkorah|first4=R. |last4=Caceres Rodriguez |first5=J.-M. |last5=Devernay |first6=M.|last6=Freitas|first7=D.|last7=Hall|first8=Å.|last8=Killingtveit|first9=Z.|last9=Liu |display-authors=4 |chapter=Hydropower|chapter-url=https://www.ipcc.ch/site/assets/uploads/2018/03/Chapter-5-Hydropower-1.pdf|pp=451, 462, 488|in=IPCC|year=2011
}}</ref>

Hydropower ranks among the energy sources with the lowest levels of greenhouse gas emissions per unit of energy produced, but levels of emissions vary enormously between projects.<ref name="AnnexIII_IPCC">{{citec |last1=Schlömer |first1=S.|first2=T.|last2=Bruckner|first3=L.|last3=Fulton|first4=E.|last4=Hertwich|display-authors=etal|year=2014|url=https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf |chapter=Annex III: Technology-specific cost and performance parameters|in=IPCC|page=1335}}</ref> The highest emissions tend to occur with large dams in tropical regions.<ref>{{Cite journal|last1=Almeida |first1=Rafael M.|last2=Shi|first2=Qinru|last3=Gomes-Selman|first3=Jonathan M.|last4=Wu|first4=Xiaojian |last5=Xue|first5=Yexiang|last6=Angarita|first6=Hector|last7=Barros|first7=Nathan|last8=Forsberg |first8=Bruce R.|last9=García-Villacorta|first9=Roosevelt|last10=Hamilton |first10=Stephen K.|last11=Melack |first11=John M.|display-authors=4|date=2019|title=Reducing greenhouse gas emissions of Amazon hydropower with strategic dam planning|journal=Nature Communications|volume=10|issue=1|pages=4281 |issn=2041-1723 |bibcode=2019NatCo..10.4281A|doi=10.1038/s41467-019-12179-5|pmc=6753097|pmid=31537792}}</ref> These emissions are produced when the biological matter that becomes submerged in the reservoir's flooding decomposes and releases carbon dioxide and methane. [[Deforestation]] and climate change can reduce energy generation from hydroelectric dams.<ref name=":15">{{Cite journal|last1=Moran|first1=Emilio F.|last2=Lopez |first2=Maria Claudia |last3=Moore|first3=Nathan|last4=Müller|first4=Norbert|last5=Hyndman|first5=David W. |display-authors=4|date=2018|title=Sustainable hydropower in the 21st century |journal=[[Proceedings of the National Academy of Sciences]] |volume=115|issue=47|pages=11891–11898|doi=10.1073/pnas.1809426115|issn=0027-8424|pmc=6255148|pmid=30397145|bibcode=2018PNAS..11511891M |doi-access=free}}</ref> Depending on location, large dams can displace residents and cause significant local environmental damage; potential [[dam failure]] could place the surrounding population at risk.<ref name=":15" />

====Geothermal====
{{Main|Geothermal power|Geothermal heating}}
[[File:Larderello Cooling Towers.jpg|thumb|Cooling towers at a geothermal power plant in [[Larderello]], Italy|alt=3 enormous waisted vertical concrete cylinders, one emitting a wisp of steam, dwarf a building in the foreground]]
[[Geothermal energy]] is produced by tapping into deep underground heat<ref name="László 1981 248–249">{{cite journal|last=László|first=Erika|year=1981|title=Geothermal Energy: An Old Ally|journal=[[Ambio]]|volume=10|issue=5|pages=248–249|jstor=4312703}}</ref> and harnessing it to generate electricity or to heat water and buildings. The use of geothermal energy is concentrated in regions where heat extraction is economical: a combination is needed of high temperatures, heat flow, and [[Permeability (Earth sciences)|permeability]] (the ability of the rock to allow fluids to pass through).{{Sfn|REN21|2020|p=97}} Power is produced from the steam created in underground reservoirs.<ref>{{Cite web|date=19 October 2009|title=Geothermal Energy Information and Facts|url=https://www.nationalgeographic.com/environment/article/geothermal-energy|url-status=dead|access-date=8 August 2021|publisher=[[National Geographic]]|archive-date=8 August 2021|archive-url=https://web.archive.org/web/20210808194416/https://www.nationalgeographic.com/environment/article/geothermal-energy}}</ref> Geothermal energy provided less than 1% of [[global energy consumption]] in 2020.<ref name=":8" />

Geothermal energy is a renewable resource because thermal energy is constantly replenished from neighbouring hotter regions and the [[radioactive decay]] of [[Naturally occurring radioactive material|naturally occurring isotopes]].{{Sfn|Soysal|Soysal|pp=222, 228|2020}} On average, the greenhouse gas emissions of geothermal-based electricity are less than 5% that of coal-based electricity.<ref name='AnnexIII_IPCC'/> Geothermal energy carries a risk of inducing earthquakes, needs effective protection to avoid water pollution, and releases toxic emissions which can be captured.{{Sfn|Soysal|Soysal|2020|pp=228–229}}

====Bioenergy====
{{Main|Bioenergy}}
{{Further|Sustainable biofuel}}
[[File:Kenyan farmer with a biogas lamp provided by USAID 2013.jpg|thumb|right|alt=Man lighting a lamp hung from the ceiling|Kenyan dairy farmer lighting a biogas lamp. [[Biogas]] produced from [[biomass]] is a renewable energy source that can be burned for cooking or light.]]
[[File:Faz S Sofia canavial 090607 REFON.JPG|thumb|right|alt=A green field of plants looking like metre high grass, surrounded by woodland with urban buildings on the far horizon|A [[Sustainable biofuel#Sugarcane in Brazil|sugarcane plantation]] to produce [[Ethanol fuel|ethanol]] in Brazil]]
Biomass is renewable organic material that comes from plants and animals.<ref>{{Cite web|date=8 June 2021|title=Biomass explained|url=https://www.eia.gov/energyexplained/biomass/|url-status=live|access-date=13 September 2021|publisher=[[US Energy Information Administration]]|archive-date=15 September 2021|archive-url=https://web.archive.org/web/20210915223913/https://www.eia.gov/energyexplained/biomass/}}</ref> It can either be burned to produce heat and electricity or be converted into [[biofuels]] such as [[biodiesel]] and ethanol, which can be used to power vehicles.<ref>{{Cite journal|last=Kopetz|first=Heinz|date=2013 |title=Build a biomass energy market|journal=[[Nature (journal)|Nature]]|volume=494|issue=7435|pages=29–31 |doi=10.1038/494029a|pmid=23389528|issn=1476-4687|doi-access=free}}</ref><ref>{{Cite journal|last=Demirbas |first=Ayhan|date=2008|title=Biofuels sources, biofuel policy, biofuel economy and global biofuel projections|url=https://www.sciencedirect.com/science/article/pii/S0196890408000770|journal=[[Energy Conversion and Management]]|volume=49|issue=8|pages=2106–2116 |doi=10.1016/j.enconman.2008.02.020 |issn=0196-8904|access-date=11 February 2021|url-status=live|archive-date=18 March 2013|archive-url=https://web.archive.org/web/20130318032539/http://www.sciencedirect.com/science/article/pii/S0196890408000770}}</ref> 

The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown.<ref name=":0">{{Cite journal|last1=Correa|first1=Diego F.|last2=Beyer|first2=Hawthorne L. |last3=Fargione |first3=Joseph E.|last4=Hill|first4=Jason D.|last5=Possingham|first5=Hugh P.|last6=Thomas-Hall|first6=Skye R.|last7=Schenk|first7=Peer M.|display-authors=4|date=2019|title=Towards the implementation of sustainable biofuel production systems|journal=[[Renewable and Sustainable Energy Reviews]]|volume=107|pages=250–263|doi=10.1016/j.rser.2019.03.005|s2cid=117472901|issn=1364-0321 |url=https://www.sciencedirect.com/science/article/pii/S136403211930139X |access-date=7 February 2021 |url-status=live|archive-date=17 July 2021|archive-url=https://web.archive.org/web/20210717132735/https://www.sciencedirect.com/science/article/abs/pii/S136403211930139X}}</ref> For example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow.<ref>{{Cite web|last=Daley |first=Jason|date=24 April 2018|title=The EPA Declared That Burning Wood Is Carbon Neutral. It's Actually a Lot More Complicated|url=https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/|url-status=live|access-date=14 September 2021|website=[[Smithsonian Magazine]]|archive-date=30 June 2021|archive-url=https://web.archive.org/web/20210630153427/https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/}}</ref> However, the establishment and cultivation of bioenergy crops can [[Land use, land-use change, and forestry|displace natural ecosystems]], [[soil retrogression and degradation|degrade soils]], and consume water resources and synthetic fertilisers.{{sfn|Tester|2012|p=512}}{{sfn|Smil|2017a|p=162}} Approximately one-third of all wood used for traditional heating and cooking in tropical areas is harvested unsustainably.{{sfn|World Health Organization|2016|p=73}} Bioenergy feedstocks typically require significant amounts of energy to harvest, dry, and transport; the energy usage for these processes may emit greenhouse gases. In some cases, the impacts of [[Indirect land use change impacts of biofuels|land-use change]], cultivation, and processing can result in higher overall carbon emissions for bioenergy compared to using fossil fuels.{{sfn|Smil|2017a|p=162}}{{sfn|IPCC|2014|p=616}} 

Use of farmland for growing biomass can result in [[food vs. fuel|less land being available for growing food]]. In the United States, around 10% of motor gasoline has been replaced by [[Corn ethanol|corn-based ethanol]], which requires a significant proportion of the harvest.<ref>{{Cite web|date=18 June 2020 |title=Biofuels explained: Ethanol|url=https://www.eia.gov/energyexplained/biofuels/ethanol.php|access-date=16 May 2021|publisher=[[US Energy Information Administration]]|archive-date=14 May 2021|archive-url=https://web.archive.org/web/20210514154634/https://www.eia.gov/energyexplained/biofuels/ethanol.php|url-status=live}}</ref><ref>{{Cite web|last=Foley|first=Jonathan |date=5 March 2013|title=It's Time to Rethink America's Corn System|url=https://www.scientificamerican.com/article/time-to-rethink-corn/|url-status=live |access-date=16 May 2021|website=[[Scientific American]]|archive-date=3 January 2020|archive-url=https://web.archive.org/web/20200103212244/https://www.scientificamerican.com/article/time-to-rethink-corn/}}</ref> In Malaysia and Indonesia, clearing forests to produce [[palm oil]] for biodiesel has led to [[Social and environmental impact of palm oil|serious social and environmental effects]], as these forests are critical [[carbon sinks]] and [[habitat]]s for diverse species.<ref>{{Cite journal|last1=Ayompe |first1=Lacour M. |last2=Schaafsma|first2=M.|last3=Egoh|first3=Benis N.|date=1 January 2021|title=Towards sustainable palm oil production: The positive and negative impacts on ecosystem services and human wellbeing |journal=[[Journal of Cleaner Production]]|volume=278|pages=123914|doi=10.1016/j.jclepro.2020.123914|s2cid=224853908 |issn=0959-6526|doi-access=free}}</ref><ref>{{Cite news|last=Lustgarten|first=Abrahm|date=20 November 2018|title=Palm Oil Was Supposed to Help Save the Planet. Instead It Unleashed a Catastrophe.|work=[[The New York Times]]|issn=0362-4331 |url=https://www.nytimes.com/2018/11/20/magazine/palm-oil-borneo-climate-catastrophe.html |access-date=15 May 2019|url-status=live|archive-date=17 May 2019|archive-url=https://web.archive.org/web/20190517044504/https://www.nytimes.com/2018/11/20/magazine/palm-oil-borneo-climate-catastrophe.html}}</ref> Since [[photosynthesis]] captures only a small fraction of the energy in sunlight, producing a given amount of bioenergy requires a large amount of land compared to other renewable energy sources.{{sfn|Smil|2017a|p=161}}

[[Second-generation biofuels]] which are produced from non-food plants or waste reduce competition with food production, but may have other negative effects including trade-offs with conservation areas and local air pollution.<ref name=":0" /> Relatively sustainable sources of biomass include [[Algae fuel|algae]], waste, and crops grown on soil unsuitable for food production.<ref name=":0" /> 

[[Carbon capture and storage]] technology can be used to capture emissions from bioenergy power plants. This process is known as [[bioenergy with carbon capture and storage]] (BECCS) and can result in net [[carbon dioxide removal]] from the atmosphere. However, BECCS can also result in net positive emissions depending on how the biomass material is grown, harvested, and transported. Deployment of BECCS at scales described in some climate change mitigation pathways would require converting large amounts of cropland.{{sfn|National Academies of Sciences, Engineering, and Medicine|2019|p=3}}

====Marine energy====
{{Main|Marine energy}}
Marine energy has the smallest share of the energy market. It includes [[Ocean Thermal Energy Conversion|OTEC]], [[tidal power]], which is approaching maturity, and [[wave power]], which is earlier in its development. Two tidal barrage systems in France and in South Korea make up 90% of global production. While single marine energy devices pose little risk to the environment, the impacts of larger devices are less well known.{{Sfn|REN21|2021|pp=113–116}}

===Non-renewable energy sources===
====Fossil fuel switching and mitigation==== <!-- This section is transcribed to [[climate change mitigation]], please keep that in mind if you change the section heading -->
Switching from [[coal]] to [[natural gas]] has advantages in terms of [[sustainability]]. For a given unit of energy produced, the [[Life-cycle greenhouse gas emissions of energy sources|life-cycle greenhouse-gas emissions]] of natural gas are around 40 times the emissions of wind or nuclear energy but are much less than coal. Burning natural gas produces around half the emissions of coal when used to generate electricity and around two-thirds the emissions of coal when used to produce heat.<ref name="IEA gas">{{cite web|date=July 2019|title=The Role of Gas: Key Findings|url=https://www.iea.org/publications/roleofgas/|access-date=4 October 2019|publisher=[[International Energy Agency|IEA]]|url-status=live|archive-date=1 September 2019|archive-url=https://web.archive.org/web/20190901022422/https://www.iea.org/publications/roleofgas/}}</ref>  Natural gas combustion also produces less air pollution than coal.<ref>{{Cite web|title=Natural gas and the environment |url=https://www.eia.gov/energyexplained/natural-gas/natural-gas-and-the-environment.php|url-status=live |access-date=28 March 2021|publisher=[[US Energy Information Administration]]|archive-date=2 April 2021 |archive-url=https://web.archive.org/web/20210402225017/https://www.eia.gov/energyexplained/natural-gas/natural-gas-and-the-environment.php}}</ref> However, natural gas is a potent greenhouse gas in itself, and [[Fugitive gas emissions|leaks during extraction and transportation]] can negate the advantages of switching away from coal.<ref name=":27">{{Cite web |last=Storrow |first=Benjamin |title=Methane Leaks Erase Some of the Climate Benefits of Natural Gas |url=https://www.scientificamerican.com/article/methane-leaks-erase-some-of-the-climate-benefits-of-natural-gas/ |access-date=31 May 2023 |website=Scientific American |language=en}}</ref> The technology to curb [[methane leaks]] is widely available but it is not always used.<ref name=":27" /> 

Switching from coal to natural gas reduces emissions in the short term and thus contributes to [[climate change mitigation]]. However, in the long term it does not provide a path to [[net-zero emissions]]. Developing natural gas infrastructure risks [[carbon lock-in]] and [[stranded assets]], where new fossil infrastructure either commits to decades of carbon emissions, or has to be written off before it makes a profit.<ref name="nytimes coal fades">{{cite web |last=Plumer|first=Brad|date=26 June 2019|title=As Coal Fades in the U.S., Natural Gas Becomes the Climate Battleground|url=https://www.nytimes.com/2019/06/26/climate/natural-gas-renewables-fight.html |access-date=4 October 2019|work=[[The New York Times]]|archive-date=23 September 2019|url-status=live|archive-url=https://web.archive.org/web/20190923092305/https://www.nytimes.com/2019/06/26/climate/natural-gas-renewables-fight.html}}</ref><ref>{{Cite journal|last1=Gürsan|first1=C.|last2=de Gooyert|first2=V. |date=2021|title=The systemic impact of a transition fuel: Does natural gas help or hinder the energy transition?|journal=[[Renewable and Sustainable Energy Reviews]]|volume=138|pages=110552|doi=10.1016/j.rser.2020.110552|s2cid=228885573 |issn=1364-0321|doi-access=free|hdl=2066/228782|hdl-access=free}}</ref>

The greenhouse gas emissions of fossil fuel and biomass power plants can be significantly reduced through carbon capture and storage (CCS). Most studies use a working assumption that CCS can capture 85–90% of the [[carbon dioxide]] ({{CO2}}) emissions from a power plant.<ref>{{Cite journal|last=Budinis|first=Sarah |date=1 November 2018|title=An assessment of CCS costs, barriers and potential|journal=[[Energy Strategy Reviews]]|volume=22|pages=61–81 |doi=10.1016/j.esr.2018.08.003|issn=2211-467X|doi-access=free}}</ref><ref>{{Cite web|date=7 January 2021|title=Zero-emission carbon capture and storage in power plants using higher capture rates |url=https://www.iea.org/articles/zero-emission-carbon-capture-and-storage-in-power-plants-using-higher-capture-rates|url-status=live|access-date=14 March 2021|publisher=[[International Energy Agency|IEA]]|archive-url=https://web.archive.org/web/20210330093543/https://www.iea.org/articles/zero-emission-carbon-capture-and-storage-in-power-plants-using-higher-capture-rates|archive-date=30 March 2021}}</ref> Even if 90% of emitted {{CO2}} is captured from a coal-fired power plant, its uncaptured emissions would still be many times greater than the emissions of nuclear, solar or wind energy per unit of electricity produced.<ref name=cleanest>{{Cite web|last=Ritchie |first=Hannah|date=10 February 2020|title=What are the safest and cleanest sources of energy?|url=https://ourworldindata.org/safest-sources-of-energy|url-status=live|access-date=14 March 2021|website=[[Our World in Data]]|archive-date=29 November 2020|archive-url=https://web.archive.org/web/20201129205209/https://ourworldindata.org/safest-sources-of-energy}}</ref><ref>{{Cite web|last=Evans|first=Simon|date=8 December 2017|title=Solar, wind and nuclear have 'amazingly low' carbon footprints, study finds|url=https://www.carbonbrief.org/solar-wind-nuclear-amazingly-low-carbon-footprints|url-status=live|access-date=15 March 2021|work=[[Carbon Brief]]|archive-date=16 March 2021 |archive-url=https://web.archive.org/web/20210316102518/https://www.carbonbrief.org/solar-wind-nuclear-amazingly-low-carbon-footprints}}</ref> Since coal plants using CCS would be less efficient, they would require more coal and thus increase the pollution associated with mining and transporting coal.{{sfn|IPCC|2018|loc=5.4.1.2}} The CCS process is expensive, with costs depending considerably on the location's proximity to suitable geology for [[Carbon sequestration|carbon dioxide storage]].<ref name=":11">{{Cite web|last=Evans|first=Simon|date=27 August 2020|title=Wind and solar are 30–50% cheaper than thought, admits UK government|url=https://www.carbonbrief.org/wind-and-solar-are-30-50-cheaper-than-thought-admits-uk-government|access-date=30 September 2020|url-status=live|archive-date=23 September 2020|archive-url=https://web.archive.org/web/20200923025247/https://www.carbonbrief.org/wind-and-solar-are-30-50-cheaper-than-thought-admits-uk-government|website=[[Carbon Brief]]}}</ref><ref>{{Cite web|last=Malischek |first=Raimund|title=CCUS in Power|url=https://www.iea.org/reports/about-ccus|access-date=30 September 2020|publisher=[[International Energy Agency|IEA]]}}</ref> Deployment of this technology is still very limited, with only 21 large-scale CCS plants in operation worldwide as of 2020.<ref>{{Cite web|last=Deign|first=Jason|date=7 December 2020|title=Carbon Capture: Silver Bullet or Mirage?|website=[[Greentech Media]]|url=https://www.greentechmedia.com/articles/read/no-clearer-if-carbon-capture-is-silver-bullet-or-mirage|access-date=14 February 2021|url-status=live|archive-url=https://web.archive.org/web/20210119013833/https://www.greentechmedia.com/articles/read/no-clearer-if-carbon-capture-is-silver-bullet-or-mirage|archive-date=19 January 2021}}</ref>

====Nuclear power====
{{Main|Nuclear power debate|Nuclear renaissance}}
[[File:Elec-fossil-nuclear-renewables.svg|thumb|upright=1.35|alt=Chart showing the proportion of electricity produced by fossil fuels, nuclear, and renewables from 1985 to 2020|Since 1985, the proportion of electricity generated from low-carbon sources has increased only slightly. Advances in deploying renewables have been mostly offset by declining shares of nuclear power.<ref>{{Cite web|last=Roser |first=Max|date=10 December 2020|title=The world's energy problem|url=https://ourworldindata.org/worlds-energy-problem |url-status=live|access-date=21 July 2021|website=[[Our World in Data]]|archive-date=21 July 2021|archive-url=https://web.archive.org/web/20210721202510/https://ourworldindata.org/worlds-energy-problem}}</ref>]]
[[Nuclear power]] has been used since the 1950s as a low-carbon source of [[Base load|baseload]] electricity.<ref>{{Cite web|last=Rhodes|first=Richard|date=19 July 2018|title=Why Nuclear Power Must Be Part of the Energy Solution |website=[[Yale Environment 360]]|publisher=[[Yale School of the Environment]] |url=https://e360.yale.edu/features/why-nuclear-power-must-be-part-of-the-energy-solution-environmentalists-climate|url-status=live|access-date=24 July 2021|archive-date=9 August 2021|archive-url=https://web.archive.org/web/20210809182424/https://e360.yale.edu/features/why-nuclear-power-must-be-part-of-the-energy-solution-environmentalists-climate}}</ref> Nuclear power plants in over 30 countries generate about 10% of global electricity.<ref>{{Cite web|last=|first=|date=June 2021|title=Nuclear Power in the World Today|publisher=[[World Nuclear Association]]|url=https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx|url-status=live|archive-url=https://web.archive.org/web/20210716094103/https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx|archive-date=16 July 2021|access-date=19 July 2021}}</ref> As of 2019, nuclear generated over a quarter of all [[low-carbon power|low-carbon energy]], making it the second largest source after hydropower.<ref name=":8">{{cite journal|url=https://ourworldindata.org/energy-mix |last1=Ritchie|first1=Hannah|last2=Roser|first2=Max|title=Energy mix|year=2020|journal=[[Our World in Data]]|url-status=live|access-date=9 July 2021 |archive-date=2 July 2021|archive-url=https://web.archive.org/web/20210702082157/https://ourworldindata.org/energy-mix}}</ref>

Nuclear power's lifecycle greenhouse gas emissions—including the mining and processing of [[uranium]]—are similar to the emissions from renewable energy sources.<ref name="AnnexIII_IPCC"/> Nuclear power uses little [[Surface power density|land per unit of energy]] produced, compared to the major renewables.  Additionally, Nuclear power does not create local air pollution.<ref>{{Cite web |last=Bailey |first=Ronald |date=10 May 2023 |title=New study: Nuclear power is humanity's greenest energy option |url=https://reason.com/2023/05/10/new-study-nuclear-power-is-humanitys-greenest-energy-option/ |access-date=22 May 2023 |website=Reason.com |language=en-US}}</ref><ref>{{cite journal|title=Nuclear Energy|url=https://ourworldindata.org/nuclear-energy |last1=Ritchie|first1=Hannah|last2=Roser|first2=Max|access-date=19 July 2021|year=2020|journal=[[Our World in Data]]|archive-url=https://web.archive.org/web/20210720063014/https://ourworldindata.org/nuclear-energy |archive-date=20 July 2021|url-status=live}}</ref> Although the [[uranium ore]] used to fuel nuclear fission plants is a non-renewable resource, enough exists to provide a supply for hundreds to thousands of years.{{sfn|MacKay|2008|p=[https://withouthotair.com/c24/page_162.shtml 162]}}<ref>{{Citec|last1=Gill |first1=Matthew|last2=Livens |first2=Francis|last3=Peakman|first3=Aiden|in=Letcher|year=2020 |chapter=Nuclear Fission|page=135}}</ref> However, uranium resources that can be accessed in an economically feasible manner, at the present state, are limited and uranium production could hardly keep up during the expansion phase.<ref>{{Cite journal|first1=Nikolaus|last1=Muellner|first2=Nikolaus|last2=Arnold |first3=Klaus|last3=Gufler|first4=Wolfgang|last4=Kromp|first5=Wolfgang |last5=Renneberg|first6=Wolfgang |last6=Liebert|date=2021|journal=Energy Policy|volume=155|at=112363|title=Nuclear energy - The solution to climate change?|doi=10.1016/j.enpol.2021.112363|s2cid=236254316|doi-access=free}}</ref> Climate change mitigation pathways consistent with ambitious goals typically see an increase in power supply from nuclear.{{sfn|IPCC|2018|loc=2.4.2.1}}

There is controversy over whether nuclear power is sustainable, in part due to concerns around [[nuclear waste]], [[nuclear proliferation|nuclear weapon proliferation]], and [[Nuclear accident|accidents]].<ref name=":14" /> Radioactive nuclear waste must be managed for thousands of years<ref name=":14">{{Citec |last1=Gill|first1=Matthew|last2=Livens|first2=Francis|last3=Peakman|first3=Aiden|in=Letcher|year=2020|pages=147–149|chapter=Nuclear Fission}}</ref> and nuclear power plants create [[fissile material]] that can be used for weapons.<ref name=":14" />  For each unit of energy produced, nuclear energy has caused far fewer [[Nuclear and radiation accidents and incidents|accidental]] and pollution-related deaths than fossil fuels, and the historic fatality rate of nuclear is comparable to renewable sources.<ref name=cleanest/> [[Public opinion on nuclear issues|Public opposition to nuclear energy]] often makes nuclear plants politically difficult to implement.<ref name=":14" /> 

Reducing the time and the cost of building new nuclear plants have been goals for decades but [[Economics of nuclear power plants|costs remain high]] and timescales long.<ref>{{cite news|last1=Timmer|first1=John |date=21 November 2020|title=Why are nuclear plants so expensive? Safety's only part of the story|website=[[Ars Technica]]|url=https://arstechnica.com/science/2020/11/why-are-nuclear-plants-so-expensive-safetys-only-part-of-the-story/|access-date=17 March 2021|url-status=live|archive-date=28 April 2021|archive-url=https://web.archive.org/web/20210428140032/https://arstechnica.com/science/2020/11/why-are-nuclear-plants-so-expensive-safetys-only-part-of-the-story/}}</ref> Various new forms of nuclear energy are in development, hoping to address the drawbacks of conventional plants. [[Fast breeder]] reactors are capable of [[Nuclear reprocessing|recycling nuclear waste]] and therefore can significantly reduce the amount of waste that requires [[Deep geological repository|geological disposal]], but have not yet been deployed on a large-scale commercial basis.<ref>{{Cite report|title=Technical assessment of nuclear energy with respect to the 'do no significant harm' criteria of Regulation (EU) 2020/852 ('Taxonomy Regulation') |url=https://ec.europa.eu/info/sites/default/files/business_economy_euro/banking_and_finance/documents/210329-jrc-report-nuclear-energy-assessment_en.pdf|publisher=[[European Commission Joint Research Centre]] |date=2021|page=53|archive-date=26 April 2021|archive-url=https://web.archive.org/web/20210426095255/https://ec.europa.eu/info/sites/default/files/business_economy_euro/banking_and_finance/documents/210329-jrc-report-nuclear-energy-assessment_en.pdf|url-status=live}}</ref> [[Thorium-based nuclear power|Nuclear power based on thorium]] (rather than uranium) may be able to provide higher energy security for countries that do not have a large supply of uranium.<ref>{{Citec |last1=Gill|first1=Matthew|last2=Livens |first2=Francis|last3=Peakman|first3=Aiden|in=Letcher|year=2020 |pages=146–147|chapter=Nuclear Fission}}</ref> [[Small modular reactors]] may have several advantages over current large reactors: It should be possible to build them faster and their modularization would allow for cost reductions via [[learning-by-doing]].<ref>{{citec|last1=Locatelli|first1=Giorgio|last2=Mignacca |first2=Benito|chapter=Small Modular Nuclear Reactors|year=2020|in=Letcher |pages=151–169 |url=https://www.sciencedirect.com/science/article/pii/B9780081028865000086}}</ref>

Several countries are attempting to develop [[Fusion power|nuclear fusion]] reactors, which would generate small amounts of waste and no risk of explosions.<ref>{{Cite news|last=McGrath|first=Matt|date=6 November 2019|title=Nuclear fusion is 'a question of when, not if'|publisher=[[BBC]] |url=https://www.bbc.com/news/science-environment-50267017|url-status=live|access-date=13 February 2021 |archive-url=https://web.archive.org/web/20210125083144/https://www.bbc.com/news/science-environment-50267017|archive-date=25 January 2021}}</ref> Although fusion power has taken steps forward in the lab, the multi-decade timescale needed to bring it to commercialization and then scale means it will not contribute to a 2050 net zero goal for climate change mitigation.<ref>{{Cite news|last=Amos|first=Jonathan|date=9 February 2022|title=Major breakthrough on nuclear fusion energy|publisher=[[BBC]]|url=https://www.bbc.com/news/science-environment-60312633|url-status=live|access-date=10 February 2022|archive-date=1 March 2022|archive-url=https://web.archive.org/web/20220301030807/https://www.bbc.com/news/science-environment-60312633}}</ref>

==Energy system transformation==
{{Main|Energy transition}}
[[File:2018- Energy transition investment versus fossil fuel investment.svg|thumb|[[Bloomberg L.P.#New Energy Finance|Bloomberg NEF]] reported that in 2022,  global energy transition investment equaled fossil fuels investment for the first time.<ref name=BloombergNEF_20230210>{{cite news |title=Energy Transition Investment Now On Par with Fossil Fuel |url=https://about.bnef.com/blog/energy-transition-investment-now-on-par-with-fossil-fuel/ |publisher=Bloomberg NEF (New Energy Finance) |date=10 February 2023 |archive-url=https://web.archive.org/web/20230327065546/https://about.bnef.com/blog/energy-transition-investment-now-on-par-with-fossil-fuel/ |archive-date=27 March 2023 |url-status=live }}</ref>]]
The emissions reductions necessary to keep global warming below 2{{Nbsp}}°C will require a system-wide transformation of the way energy is produced, distributed, stored, and consumed.{{sfn|United Nations Environment Programme|2019|p=46}} For a society to replace one form of energy with another, multiple technologies and behaviours in the energy system must change. For example, transitioning from oil to solar power as the energy source for cars requires the generation of solar electricity, modifications to the electrical grid to accommodate fluctuations in solar panel output or the introduction of variable battery chargers and higher overall demand, adoption of [[electric cars]], and networks of [[Electric vehicle charging network|electric vehicle charging]] facilities and repair shops.{{sfn|Jaccard|2020|loc=[https://www.cambridge.org/core/books/citizens-guide-to-climate-success/renewables-have-won/F64DF99C3ED79CEA29C6EE2A59E71AB3/core-reader Chapter 11 – "Renewables Have Won"]|pp=202–203}}   

Many climate change mitigation pathways envision three main aspects of a low-carbon energy system: 

* The use of low-emission energy sources to produce electricity
* [[Electrification]] – that is increased use of electricity instead of directly burning fossil fuels
* Accelerated adoption of energy efficiency measures{{sfn|IPCC|2014|loc=7.11.3}}

Some energy-intensive technologies and processes are difficult to electrify, including aviation, shipping, and steelmaking. There are several options for reducing the emissions from these sectors: biofuels and synthetic [[carbon-neutral fuels]] can power many vehicles that are designed to burn fossil fuels, however biofuels cannot be sustainably produced in the quantities needed and synthetic fuels are currently very expensive.{{sfn|IEA|2021|pp=106–110}} For some applications, the most prominent alternative to electrification is to develop a system based on sustainably-produced [[hydrogen fuel]].<ref name=":18" />    

Full decarbonisation of the global energy system is expected to take several decades and can mostly be achieved with existing technologies.{{sfn|Jaccard|2020|loc=[https://www.cambridge.org/core/books/citizens-guide-to-climate-success/renewables-have-won/F64DF99C3ED79CEA29C6EE2A59E71AB3/core-reader Chapter 11 – "Renewables Have Won"]|p=203}} The IEA states that further innovation in the energy sector, such as in battery technologies and carbon-neutral fuels, is needed to reach net-zero emissions by 2050.{{sfn|IEA|2021|p=15}} Developing new technologies requires research and development, [[technology demonstration|demonstration]], and [[experience curve|cost reductions via deployment]].{{sfn|IEA|2021|p=15}} The transition to a zero-carbon energy system will bring strong [[Co-benefits of climate change mitigation|co-benefits]] for human health: The [[World Health Organization]] estimates that efforts to limit global warming to 1.5&nbsp;°C could save millions of lives each year from reductions to air pollution alone.{{sfn|World Health Organization|2018|loc=Executive Summary}}<ref name="Vandyck_et_al_2018">{{cite journal|last1=Vandyck|first1=T.|last2=Keramidas|first2=K.|last3=Kitous|first3=A.|last4=Spadaro|first4=J.V.|display-authors=etal|year=2018|title=Air quality co-benefits for human health and agriculture counterbalance costs to meet Paris Agreement pledges.|journal=[[Nature Communications]]|volume=9|issue=1|pages=4939|doi=10.1038/s41467-018-06885-9|pmc=6250710|pmid=30467311|bibcode=2018NatCo...9.4939V}}</ref> With good planning and management, pathways exist to provide universal [[Rural electrification|access to electricity]] and [[clean cooking]] by 2030 in ways that are consistent with climate goals.{{sfn|United Nations Environment Programme|2019|pp=46–55}}<ref>{{harvnb|IPCC|2018|p=97}}</ref> Historically, several countries have made rapid economic gains through coal usage.{{sfn|United Nations Environment Programme|2019|pp=46–55}} However, there remains a window of opportunity for many poor countries and regions to "[[Leapfrogging|leapfrog]]" fossil fuel dependency by developing their energy systems based on renewables, given adequate international investment and knowledge transfer.{{sfn|United Nations Environment Programme|2019|pp=46–55}}

===Integrating variable energy sources===
[[File:SoSie+SoSchiff Ansicht.jpg|thumb|alt=Short terraces of houses, with their entire sloping roofs covered with solar panels| Buildings in the [[Solar Settlement at Schlierberg]], Germany, produce more energy than they consume. They incorporate rooftop solar panels and are built for maximum energy efficiency.<ref>{{Cite journal|last=Hopwood|first=David|date=2007|title=Blueprint for sustainability?: What lessons can we learn from Freiburg's inclusive approach to sustainable development?|url=https://www.sciencedirect.com/science/article/pii/S1471084607700689|journal=[[Refocus]]|volume=8|issue=3|pages=54–57|doi=10.1016/S1471-0846(07)70068-9|issn=1471-0846|access-date=17 October 2021|archive-date=2 November 2021|archive-url=https://web.archive.org/web/20211102023331/https://www.sciencedirect.com/science/article/abs/pii/S1471084607700689|url-status=live}}</ref>]]
To deliver reliable electricity from [[variable renewable energy]] sources such as wind and solar, electrical power systems require flexibility.{{sfn|United Nations Environment Programme|2019|p=47}} Most [[electrical grid]]s were constructed for non-intermittent energy sources such as coal-fired power plants.<ref>{{Cite web|title=Introduction to System Integration of Renewables |url=https://www.iea.org/reports/introduction-to-system-integration-of-renewables|publisher=[[International Energy Agency|IEA]]|access-date=30 May 2020|archive-date=15 May 2020|archive-url=https://web.archive.org/web/20200515213454/https://www.iea.org/reports/introduction-to-system-integration-of-renewables|url-status=dead}}</ref> As larger amounts of solar and wind energy are integrated into the grid, changes have to be made to the energy system to ensure that the supply of electricity is matched to demand.<ref name=":13">{{Cite journal|last1=Blanco|first1=Herib|last2=Faaij|first2=André|date=2018|title=A review at the role of storage in energy systems with a focus on Power to Gas and long-term storage|journal=[[Renewable and Sustainable Energy Reviews]]|volume=81|pages=1049–1086|doi=10.1016/j.rser.2017.07.062|issn=1364-0321|doi-access=free|url=https://pure.rug.nl/ws/files/47678895/A_review_at_the_role_of_storage_in_energy_systems.pdf}}</ref> In 2019, these sources generated 8.5% of worldwide electricity, a share that has grown rapidly.<ref name=":4" />

There are various ways to make the electricity system more flexible. In many places, wind and solar generation are complementary on a daily and a seasonal scale: there is more wind during the night and in winter when solar energy production is low.<ref name=":13" /> Linking different geographical regions through [[High-voltage direct current|long-distance transmission lines]] allows for further cancelling out of variability.{{Sfn|REN21|2020|p=177}} Energy demand can be shifted in time through [[energy demand management]] and the use of [[smart grids]], matching the times when variable energy production is highest. With [[grid energy storage]], energy produced in excess can be released when needed.<ref name=":13" /> Further flexibility could be provided from [[sector coupling]], that is coupling the electricity sector to the heat and mobility sector via [[power-to-heat]]-systems and electric vehicles.<ref>{{Cite journal|last1=Bloess|first1=Andreas|last2=Schill|first2=Wolf-Peter|last3=Zerrahn|first3=Alexander|date=2018|title=Power-to-heat for renewable energy integration: A review of technologies, modeling approaches, and flexibility potentials|journal=[[Applied Energy]]|volume=212|pages=1611–1626|doi=10.1016/j.apenergy.2017.12.073|s2cid=116132198 |doi-access=free|bibcode=2018ApEn..212.1611B |hdl=10419/200120|hdl-access=free}}</ref>

Building overcapacity for wind and solar generation can help ensure that enough electricity is produced even during poor weather. In optimal weather, energy generation may have to be [[Curtailment (electricity)|curtailed]] if excess electricity cannot be used or stored. The final demand-supply mismatch may be covered by using [[Dispatchable generation|dispatchable energy sources]] such as hydropower, bioenergy, or natural gas.{{Sfn|IEA|2020|p=109}}

====Energy storage====
{{Main|Energy storage|Grid energy storage}}
[[File:1 MW 4 MWh Turner Energy Storage Project in Pullman, WA.jpg|thumb|Battery storage facility|alt=Photo with a set of white containers]]Energy storage helps overcome barriers to intermittent renewable energy and is an important aspect of a sustainable energy system.<ref name=":16">{{Cite journal|last1=Koohi-Fayegh|first1=S.|last2=Rosen|first2=M.A.|date=2020|title=A review of energy storage types, applications and recent developments|url=https://www.sciencedirect.com/science/article/pii/S2352152X19306012|journal=[[Journal of Energy Storage]]|volume=27|pages=101047|doi=10.1016/j.est.2019.101047|s2cid=210616155|issn=2352-152X|access-date=28 November 2020|archive-date=17 July 2021|archive-url=https://web.archive.org/web/20210717132743/https://www.sciencedirect.com/science/article/abs/pii/S2352152X19306012|url-status=live}}</ref> The most commonly used and available storage method is [[pumped-storage hydroelectricity]], which requires locations with large differences in height and access to water.<ref name=":16" /> [[Battery storage|Batteries]], especially [[Lithium-ion battery|lithium-ion batteries]], are also deployed widely.<ref>{{Cite web|last=Katz|first=Cheryl|date=17 December 2020|title=The batteries that could make fossil fuels obsolete|url=https://www.bbc.com/future/article/20201217-renewable-power-the-worlds-largest-battery|url-status=live|archive-url=https://web.archive.org/web/20210111075439/https://www.bbc.com/future/article/20201217-renewable-power-the-worlds-largest-battery|archive-date=11 January 2021|access-date=10 January 2021|publisher=[[BBC]]}}</ref>  Batteries typically store electricity for short periods; research is ongoing into technology with sufficient capacity to last through seasons.<ref>{{Cite journal|last1=Herib|first1=Blanco|last2=André|first2=Faaij|date=2018|title=A review at the role of storage in energy systems with a focus on Power to Gas and long-term storage|journal=[[Renewable and Sustainable Energy Reviews]]|volume=81|pages=1049–1086|doi=10.1016/j.rser.2017.07.062|issn=1364-0321|doi-access=free|url=https://pure.rug.nl/ws/files/47678895/A_review_at_the_role_of_storage_in_energy_systems.pdf}}</ref> Costs of utility-scale batteries in the US have fallen by around 70% since 2015, however the cost and low [[energy density]] of batteries makes them impractical for the very large energy storage needed to balance inter-seasonal  variations in energy production.<ref name=":2">{{Cite book|date=19 May 2021|title=Climate change: science and solutions|url=https://royalsociety.org/topics-policy/projects/climate-change-science-solutions/|chapter=Climate change and batteries: the search for future power storage solutions|chapter-url=https://royalsociety.org/-/media/policy/projects/climate-change-science-solutions/climate-science-solutions-batteries.pdf|url-status=live|access-date=15 October 2021|publisher=[[The Royal Society]]|archive-date=16 October 2021|archive-url=https://web.archive.org/web/20211016023551/https://royalsociety.org/topics-policy/projects/climate-change-science-solutions/}}</ref> Pumped hydro storage and [[power-to-gas]] (converting electricity to gas and back) with capacity for multi-month usage has been implemented in some locations.<ref>{{Cite journal|last1=Hunt|first1=Julian D.|last2=Byers|first2=Edward|last3=Wada|first3=Yoshihide|last4=Parkinson|first4=Simon|last5=Gernaat|first5=David E. H. J.|last6=Langan|first6=Simon|last7=van Vuuren|first7=Detlef P.|last8=Riahi|first8=Keywan|display-authors=4|date=2020|title=Global resource potential of seasonal pumped hydropower storage for energy and water storage|journal=[[Nature Communications]]|volume=11|issue=1|pages=947|doi=10.1038/s41467-020-14555-y|pmid=32075965|pmc=7031375|bibcode=2020NatCo..11..947H|issn=2041-1723|doi-access=free}}</ref><ref>{{Cite web|last=Balaraman|first=Kavya|date=12 October 2020|title=To batteries and beyond: With seasonal storage potential, hydrogen offers 'a different ballgame entirely'|url=https://www.utilitydive.com/news/to-batteries-and-beyond-with-seasonal-storage-potential-hydrogen-offers/584959/|url-status=live|archive-url=https://web.archive.org/web/20210118052735/https://www.utilitydive.com/news/to-batteries-and-beyond-with-seasonal-storage-potential-hydrogen-offers/584959/|archive-date=18 January 2021|access-date=10 January 2021|website=Utility Dive}}</ref>

=== Electrification ===
{{main|Electrification}}

[[File:Heat Pump.jpg|thumb|alt=Photograph two fans, the outdoor section of a heat pump|The outdoor section of a [[heat pump]]. In contrast to oil and gas boilers, they use electricity and are highly efficient. As such, electrification of heating can significantly reduce emissions.<ref>{{Cite web|last=Cole|first=Laura|date=15 November 2020|title=How to cut carbon out of your heating|url=https://www.bbc.com/future/article/20201116-climate-change-how-to-cut-the-carbon-emissions-from-heating|url-status=live|access-date=31 August 2021|publisher=[[BBC]]|archive-date=27 August 2021|archive-url=https://web.archive.org/web/20210827063629/https://www.bbc.com/future/article/20201116-climate-change-how-to-cut-the-carbon-emissions-from-heating}}</ref>  ]]
Compared to the rest of the energy system, emissions can be reduced much faster in the electricity sector.{{sfn|IPCC|2014|loc=7.11.3}} As of 2019, 37% of global electricity is produced from low-carbon sources (renewables and nuclear energy). Fossil fuels, primarily coal, produce the rest of the electricity supply.<ref>{{Cite journal|last1=Ritchie|first1=Hannah|last2=Roser|first2=Max|date=2020|title=Electricity Mix |url=https://ourworldindata.org/electricity-mix|journal=[[Our World in Data]]|access-date=16 October 2021|archive-date=13 October 2021|archive-url=https://web.archive.org/web/20211013212634/https://ourworldindata.org/electricity-mix|url-status=live}}</ref> One of the easiest and fastest ways to reduce greenhouse gas emissions is to phase out coal-fired power plants and increase renewable electricity generation.{{sfn|IPCC|2014|loc=7.11.3}}  

Climate change mitigation pathways envision extensive electrification—the use of electricity as a substitute for the direct burning of fossil fuels for heating buildings and for transport.{{sfn|IPCC|2014|loc=7.11.3}} Ambitious climate policy would see a doubling of energy share consumed as electricity by 2050, from 20% in 2020.{{sfn|IPCC|2018|loc=2.4.2.2}} 

One of the challenges in providing universal access to electricity is distributing power to rural areas. Off-grid and [[Mini-grids|mini-grid]] systems based on renewable energy, such as small solar PV installations that generate and store enough electricity for a village, are important solutions.{{sfn|IEA|2021|pp=167–169}} Wider access to reliable electricity would lead to less use of [[kerosene lighting]] and diesel generators, which are currently common in the developing world.{{sfn|United Nations Development Programme|2016|p=30}} 

Infrastructure for generating and storing renewable electricity requires minerals and metals, such as [[cobalt]] and [[lithium]] for batteries and [[copper]] for solar panels.<ref name=":19">{{Cite journal|last=Herrington|first=Richard|date=2021|title=Mining our green future|journal=[[Nature Reviews Materials]]|volume=6|issue=6|pages=456–458|bibcode=2021NatRM...6..456H|doi=10.1038/s41578-021-00325-9|issn=2058-8437|doi-access=free}}</ref> Recycling can meet some of this demand if product lifecycles are well-designed, however achieving net zero emissions would still require major increases in mining for 17 types of metals and minerals.<ref name=":19" /> A small group of countries or companies sometimes dominate the markets for these commodities, raising geopolitical concerns.<ref name=":20">{{Citec|last=Mudd|first=Gavin M.|year=2020|in=Letcher|pp=723–724|chapter=Metals and Elements Needed to Support Future Energy Systems}}</ref> Most of the world's cobalt, for instance, is [[Mining industry of the Democratic Republic of the Congo|mined in the Democratic Republic of the Congo]], a politically unstable region where mining is often associated with human rights risks.<ref name=":19" /> More diverse geographical sourcing may ensure a more flexible and less brittle [[supply chain]].<ref>{{Cite journal|last=Babbitt|first=Callie W.|date=2020|title=Sustainability perspectives on lithium-ion batteries|journal=[[Clean Technologies and Environmental Policy]]|volume=22|issue=6|pages=1213–1214|doi=10.1007/s10098-020-01890-3|issn=1618-9558|doi-access=free|bibcode=2020CTEP...22.1213B |s2cid=220351269}}</ref>

===Hydrogen===
{{Main|Hydrogen economy}}

Hydrogen gas is widely discussed in the context of energy, as an energy carrier with potential to reduce greenhouse gas emissions.{{sfn|IPCC AR6 WG3|2022|pp=91-92}}<ref>{{Cite web |last1=Evans |first1=Simon |last2=Gabbatiss |first2=Josh |date=30 November 2020 |title=In-depth Q&A: Does the world need hydrogen to solve climate change? |url=https://www.carbonbrief.org/in-depth-qa-does-the-world-need-hydrogen-to-solve-climate-change |url-status=live |archive-url=https://web.archive.org/web/20201201155033/https://www.carbonbrief.org/in-depth-qa-does-the-world-need-hydrogen-to-solve-climate-change |archive-date=1 December 2020 |access-date=1 December 2020 |website=[[Carbon Brief]]}}</ref> This requires hydrogen to be produced cleanly, in quantities to supply in sectors and applications where cheaper and more energy efficient [[Climate change mitigation|mitigation]] alternatives are limited. These applications include heavy industry and long-distance transport.{{sfn|IPCC AR6 WG3|2022|pp=91-92}}

Hydrogen can be deployed as an energy source in [[fuel cells]] to produce electricity, or via combustion to generate heat.<ref name=":0422">{{Cite journal |last=Lewis |first=Alastair C. |date=10 June 2021 |title=Optimising air quality co-benefits in a hydrogen economy: a case for hydrogen-specific standards for NO x emissions |journal=Environmental Science: Atmospheres |language=en |volume=1 |issue=5 |pages=201–207 |doi=10.1039/D1EA00037C|doi-access=free }}{{Creative Commons text attribution notice|cc=by3|url=|authors=|vrt=|from this source=yes}}</ref> When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapour.<ref name=":0422" /> Combustion of hydrogen can lead to the thermal formation of harmful [[NOx|nitrogen oxides]].<ref name=":0422" /> The overall lifecycle emissions of hydrogen depend on how it is produced. Nearly all of the world's current supply of hydrogen is created from fossil fuels.<ref>{{Cite news|last1=Reed|first1=Stanley|last2=Ewing|first2=Jack|date=13 July 2021|title=Hydrogen Is One Answer to Climate Change. Getting It Is the Hard Part.|work=[[The New York Times]]|url=https://www.nytimes.com/2021/07/13/business/hydrogen-climate-change.html|access-date=14 July 2021|issn=0362-4331|archive-date=14 July 2021|archive-url=https://web.archive.org/web/20210714190628/https://www.nytimes.com/2021/07/13/business/hydrogen-climate-change.html|url-status=live}}</ref><ref>{{harvnb|IRENA|2019|p=9}}.</ref> The main method is [[steam methane reforming]], in which hydrogen is produced from a chemical reaction between steam and [[methane]], the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide.<ref name=":7">{{Cite web|last1=Bonheure|first1=Mike|last2=Vandewalle|first2=Laurien A.|last3=Marin|first3=Guy B.|last4=Van Geem|first4=Kevin M.|date=March 2021|title=Dream or Reality? Electrification of the Chemical Process Industries|url=https://www.aiche-cep.com/cepmagazine/march_2021/MobilePagedArticle.action?articleId=1663852|url-status=live|archive-url=https://web.archive.org/web/20210717132733/https://www.aiche-cep.com/cepmagazine/march_2021/MobilePagedArticle.action?articleId=1663852|archive-date=17 July 2021|access-date=6 July 2021|website=CEP Magazine|publisher=[[American Institute of Chemical Engineers]]}}</ref> While [[carbon capture and storage]] (CCS) could remove a large fraction of these emissions, the overall carbon footprint of hydrogen from natural gas is difficult to assess {{As of|2021|lc=y}}, in part because of emissions (including [[Gas venting|vented]] and [[Fugitive gas emissions|fugitive]] [[methane]]) created in the production of the natural gas itself.<ref name=":25">{{Cite journal|date=2021|title=Industrial decarbonization via hydrogen: A critical and systematic review of developments, socio-technical systems and policy options|url=http://sro.sussex.ac.uk/id/eprint/108187/1/Griffiths-IDRIC-Hydrogen-Manuscript-REV1_v1.1_tracked-BKS%5B90%5D.pdf|journal=[[Energy Research & Social Science]]|volume=80|page=39|doi=10.1016/j.erss.2021.102208|issn=2214-6296|first1=Steve|last1=Griffiths|first2=Benjamin K.|last2=Sovacool|first3=Jinsoo|last3=Kim|first4=Morgan|last4=Bazilian|first5=Joao M.|last5=Uratani|display-authors=4|access-date=11 September 2021|url-access=}}</ref> 

Electricity can be used to split water molecules, producing sustainable hydrogen provided the electricity was generated sustainably. However, this [[electrolysis]] process is currently financially more expensive than creating hydrogen from methane without CCS and the efficiency of energy conversion is inherently low.<ref name=":18">{{Cite web|last1=Evans|first1=Simon|last2=Gabbatiss|first2=Josh|date=30 November 2020|title=In-depth Q&A: Does the world need hydrogen to solve climate change?|url=https://www.carbonbrief.org/in-depth-qa-does-the-world-need-hydrogen-to-solve-climate-change|access-date=1 December 2020|website=[[Carbon Brief]]|archive-date=1 December 2020|archive-url=https://web.archive.org/web/20201201155033/https://www.carbonbrief.org/in-depth-qa-does-the-world-need-hydrogen-to-solve-climate-change|url-status=live}}</ref> Hydrogen can be produced when there is a surplus of [[Variable renewable energy|variable renewable electricity]], then stored and used to generate heat or to re-generate electricity.<ref>{{Cite journal|last1=Palys|first1=Matthew J.|last2=Daoutidis|first2=Prodromos|date=2020|title=Using hydrogen and ammonia for renewable energy storage: A geographically comprehensive techno-economic study|journal=[[Computers & Chemical Engineering]]|volume=136|pages=106785|doi=10.1016/j.compchemeng.2020.106785|osti=1616471 |issn=0098-1354|doi-access=free}}</ref> It can be further transformed into liquid fuels such as [[green ammonia]] and [[green methanol]].{{Sfn|IRENA|2021|pp=12, 22}} Innovation in [[Electrolysis of water|hydrogen electrolysers]] could make large-scale production of hydrogen from electricity [[Hydrogen economy#Costs|more cost-competitive]].{{sfn|IEA|2021|pp=15, 75–76}}  

Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonisation of industry alongside other technologies, such as [[electric arc furnace]]s for steelmaking.<ref>{{Cite web |last=Kjellberg-Motton |first=Brendan |date=7 February 2022 |title=Steel decarbonisation gathers speed {{!}} Argus Media |url=https://www.argusmedia.com/en//news/2299399-steel-decarbonisation-gathers-speed |access-date=7 September 2023 |website=www.argusmedia.com |language=en}}</ref> For steelmaking, hydrogen can function as a clean energy carrier and simultaneously as a low-carbon catalyst replacing coal-derived [[coke (fuel)|coke]].<ref>{{Cite web|last1=Blank|first1=Thomas|last2=Molly|first2=Patrick|date=January 2020|title=Hydrogen's Decarbonization Impact for Industry|url=https://rmi.org/wp-content/uploads/2020/01/hydrogen_insight_brief.pdf|pages=2, 7, 8|url-status=live|archive-url=https://web.archive.org/web/20200922115313/https://rmi.org/wp-content/uploads/2020/01/hydrogen_insight_brief.pdf|archive-date=22 September 2020|access-date=|publisher=[[Rocky Mountain Institute]]}}</ref> Hydrogen used to decarbonise transportation is likely to find its largest applications in shipping, aviation and to a lesser extent heavy goods vehicles.{{sfn|IPCC AR6 WG3|2022|pp=91–92}} For light duty vehicles including passenger cars, hydrogen is far behind other [[alternative fuel vehicle]]s, especially compared with the rate of adoption of [[battery electric vehicles]], and may not play a significant role in future.<ref>{{Cite journal |last=Plötz |first=Patrick |date=31 January 2022 |title=Hydrogen technology is unlikely to play a major role in sustainable road transport |url=https://www.nature.com/articles/s41928-021-00706-6 |journal=Nature Electronics |language=en |volume=5 |issue=1 |pages=8–10 |doi=10.1038/s41928-021-00706-6 |s2cid=246465284 |issn=2520-1131}}</ref>

Disadvantages of hydrogen as an energy carrier include high costs of storage and distribution due to hydrogen's explosivity, its large volume compared to other fuels, and its tendency to make pipes brittle.<ref name=":25" />

=== Energy usage technologies ===

====Transport====
[[File:Hornby Street Separated Bike Lane.jpg|thumb|right|alt=Group of cyclists using a bike lane in Vancouver, Canada|[[Utility cycling]] infrastructure, such as this [[bike lane]] in [[Vancouver]], encourages sustainable transport.<ref>{{cite journal |last1=Fraser |first1=Simon D.S. |last2=Lock |first2=Karen |title=Cycling for transport and public health: a systematic review of the effect of the environment on cycling |journal=[[European Journal of Public Health]] |date=December 2011 |volume=21 |issue=6 |pages=738–743 |doi=10.1093/eurpub/ckq145 |pmid=20929903 |doi-access=free }}</ref>]]
{{main|Sustainable transport}}
Transport accounts for 14% of global greenhouse gas emissions,<ref>{{Cite web|date=12 January 2016|title=Global Greenhouse Gas Emissions Data|url=https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data|access-date=15 October 2021|publisher=[[United States Environmental Protection Agency]]|archive-date=5 December 2019|archive-url=https://web.archive.org/web/20191205123907/https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data|url-status=live}}</ref> but there are multiple ways to make transport more sustainable. [[Public transport]] typically emits fewer greenhouse gases per passenger than personal vehicles, since trains and buses can carry many more passengers at once.<ref>{{Cite journal|last=Bigazzi|first=Alexander|date=2019|title=Comparison of marginal and average emission factors for passenger transportation modes|url=https://www.sciencedirect.com/science/article/pii/S030626191930580X|journal=[[Applied Energy]]|volume=242|pages=1460–1466|doi=10.1016/j.apenergy.2019.03.172|bibcode=2019ApEn..242.1460B |s2cid=115682591|issn=0306-2619|access-date=8 February 2021|archive-date=17 July 2021|archive-url=https://web.archive.org/web/20210717132723/https://www.sciencedirect.com/science/article/abs/pii/S030626191930580X|url-status=live}}</ref><ref>{{Cite journal|last1=Schäfer|first1=Andreas W.|last2=Yeh|first2=Sonia|date=2020|title=A holistic analysis of passenger travel energy and greenhouse gas intensities|url=https://discovery.ucl.ac.uk/10096557/1/Energy%26GHG_Intensity.pdf|journal=[[Nature Sustainability]]|volume=3|issue=6|pages=459–462|doi=10.1038/s41893-020-0514-9|bibcode=2020NatSu...3..459S |s2cid=216032098|issn=2398-9629|via=|url-access=}}</ref> Short-distance flights can be replaced by [[high-speed rail]], which is more efficient, especially when electrified.{{sfn|United Nations Environment Programme|2020|p=xxv}}{{sfn|IEA|2021|p=137}} Promoting non-motorised transport such as walking and cycling, particularly in cities, can make transport cleaner and healthier.<ref>{{Cite journal|last1=Pucher|first1=John|last2=Buehler|first2=Ralph|date=2017|title=Cycling towards a more sustainable transport future|journal=[[Transport Reviews]]|volume=37|issue=6|pages=689–694|doi=10.1080/01441647.2017.1340234|issn=0144-1647|doi-access=free}}</ref><ref>{{Cite web|last=Smith|first=John|date=22 September 2016|title=Sustainable transport|url=https://transport.ec.europa.eu/transport-themes/sustainable-transport_en|access-date=22 October 2021|publisher=[[European Commission]]|url-status=live|archive-date=22 October 2021|archive-url=https://web.archive.org/web/20211022074150/https://transport.ec.europa.eu/transport-themes/sustainable-transport_en}}</ref> 

The [[Energy efficiency in transport|energy efficiency of cars]] has increased over time,<ref>{{Cite journal|last1=Knobloch|first1=Florian|last2=Hanssen|first2=Steef V.|last3=Lam|first3=Aileen|last4=Pollitt|first4=Hector |last5=Salas|first5=Pablo|last6=Chewpreecha|first6=Unnada |last7=Huijbregts|first7=Mark A. J.|last8=Mercure|first8=Jean-Francois|display-authors=4 |date=2020|title=Net emission reductions from electric cars and heat pumps in 59 world regions over time|journal=[[Nature Sustainability]]|volume=3|issue=6|pages=437–447|doi=10.1038/s41893-020-0488-7|pmid=32572385|issn=2398-9629|pmc=7308170|bibcode=2020NatSu...3..437K }}</ref> but shifting to [[electric vehicle]]s is an important further step towards decarbonising transport and reducing air pollution.<ref name=":17">{{Cite journal|last1=Bogdanov|first1=Dmitrii|last2=Farfan|first2=Javier|last3=Sadovskaia|first3=Kristina|last4=Aghahosseini|first4=Arman|last5=Child|first5=Michael|last6=Gulagi|first6=Ashish|last7=Oyewo|first7=Ayobami Solomon|last8=de Souza Noel Simas Barbosa|first8=Larissa|last9=Breyer|first9=Christian|display-authors=4|date=2019|title=Radical transformation pathway towards sustainable electricity via evolutionary steps|url=|journal=[[Nature Communications]]|volume=10|issue=1|pages=1077|bibcode=2019NatCo..10.1077B|doi=10.1038/s41467-019-08855-1|issn=|pmc=6403340|pmid=30842423}}</ref> A large proportion of traffic-related air pollution consists of particulate matter from road dust and the wearing-down of tyres and brake pads.<ref>{{Cite book|last1=Martini|first1=Giorgio|url=https://publications.jrc.ec.europa.eu/repository/handle/JRC89231|title=Non-exhaust traffic related emissions – Brake and tyre wear PM. EUR 26648.|last2=Grigoratos|first2=Theodoros|date=2014|publisher=[[Publications Office of the European Union]]|isbn=978-92-79-38303-8|pages=42|oclc=1044281650|archive-date=30 July 2021|archive-url=https://web.archive.org/web/20210730193639/https://publications.jrc.ec.europa.eu/repository/handle/JRC89231|url-status=live}}</ref> Substantially reducing pollution from these [[Non-tailpipe emissions|non-tailpipe]] sources cannot be achieved by electrification; it requires measures such as making vehicles lighter and driving them less.<ref>{{Cite book| url=https://www.oecd-ilibrary.org/environment/non-exhaust-particulate-emissions-from-road-transport_4a4dc6ca-en|title=Non-exhaust Particulate Emissions from Road Transport: An Ignored Environmental Policy Challenge|date=2020|publisher=[[OECD]] Publishing|isbn=978-92-64-45244-2|pages=8–9|chapter=Executive Summary|doi=10.1787/4a4dc6ca-en|s2cid=136987659|archive-date=30 July 2021|archive-url=https://web.archive.org/web/20210730195154/https://www.oecd-ilibrary.org/environment/non-exhaust-particulate-emissions-from-road-transport_4a4dc6ca-en|url-status=live}}</ref> Light-duty cars in particular are a prime candidate for decarbonization using [[Electric battery|battery technology]]. 25% of the world's [[Carbon dioxide|{{CO2}}]] emissions still originate from the transportation sector.<ref>{{Cite web |title={{CO2}} performance of new passenger cars in Europe |url=https://www.eea.europa.eu/ims/co2-performance-of-new-passenger |access-date=19 October 2022 |website=www.eea.europa.eu |language=en}}</ref>    

Long-distance freight transport and aviation are difficult sectors to electrify with current technologies, mostly because of the weight of [[Electric vehicle battery|batteries]] needed for long-distance travel, battery recharging times, and limited battery lifespans.{{sfn|IEA|2021|pp=133–137}}<ref name=":2" />  Where available, freight transport by ship [[Rail freight transport|and rail]] is generally more sustainable than by air and by road.<ref>{{Cite web|title=Rail and waterborne – best for low-carbon motorised transport|publisher=[[European Environment Agency]]|url=https://www.eea.europa.eu/publications/rail-and-waterborne-transport|access-date=15 October 2021|archive-date=9 October 2021|archive-url=https://web.archive.org/web/20211009064539/https://www.eea.europa.eu/publications/rail-and-waterborne-transport|url-status=live}}</ref> [[Hydrogen vehicles]] may be an option for larger vehicles such as lorries.<ref>{{Cite web|last=Miller|first=Joe|date=9 September 2020|title=Hydrogen takes a back seat to electric for passenger vehicles|url=https://www.ft.com/content/98a386ee-1a04-40fd-b6a4-8cf13ff1d0da|access-date=9 September 2020|website=[[Financial Times]]|archive-date=20 September 2020|archive-url=https://web.archive.org/web/20200920154027/https://www.ft.com/content/98a386ee-1a04-40fd-b6a4-8cf13ff1d0da|url-status=live}}</ref> Many of the techniques needed to lower emissions from shipping and aviation are still early in their development, with [[ammonia]] (produced from hydrogen) a promising candidate for shipping fuel.{{Sfn|IEA|2021|pp=136, 139}} [[Aviation biofuel]] may be one of the better uses of bioenergy if emissions are captured and stored during manufacture of the fuel.<ref name="Biomass in a low-carbon economy">{{Cite report|url=https://www.theccc.org.uk/publication/biomass-in-a-low-carbon-economy/|title=Biomass in a low-carbon economy|date=November 2018|publisher=UK [[Committee on Climate Change]]|page=18|access-date=28 December 2019|archive-date=28 December 2019|archive-url=https://web.archive.org/web/20191228191428/https://www.theccc.org.uk/publication/biomass-in-a-low-carbon-economy/|url-status=live}}</ref>

====Buildings and cooking====
{{Further|Renewable heat|Green building|Energy poverty and cooking}}
[[File:Aghazade mansion.jpg|thumb|alt=Building with windcatcher towers|[[Passive cooling]] features, such as these [[windcatcher]] towers in Iran, bring cool air into buildings without any use of energy.<ref>{{Cite web|last=Abdolhamidi|first=Shervin|date=27 September 2018|title=An ancient engineering feat that harnessed the wind|url=https://www.bbc.com/travel/article/20180926-an-ancient-engineering-feat-that-harnessed-the-wind|url-status=live|access-date=12 August 2021|publisher=[[BBC]]|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812203754/https://www.bbc.com/travel/article/20180926-an-ancient-engineering-feat-that-harnessed-the-wind}}</ref>]] 
[[File:Kookplaat inductie.JPG|thumb|alt=Electric induction oven|For cooking, [[Induction cooking|electric induction stoves]] are one of the most energy-efficient and safest options.{{sfn|Smith|Pillarisetti |2017|pp=145–146}}<ref>{{Cite web|publisher=[[Natural Resources Canada]]|date=16 January 2013|title=Cooking appliances|url=https://www.nrcan.gc.ca/energy-efficiency/products/product-information/appliances-for-residential-use/cooking-appliances/13987|url-status=live|access-date=30 July 2021|archive-date=30 July 2021|archive-url=https://web.archive.org/web/20210730185801/https://www.nrcan.gc.ca/energy-efficiency/products/product-information/appliances-for-residential-use/cooking-appliances/13987}}</ref>]]
Over one-third of energy use is in buildings and their construction.<ref>{{Cite web|title=Buildings|url=https://www.iea.org/topics/buildings|access-date=15 October 2021|publisher=[[International Energy Agency|IEA]]|archive-date=14 October 2021|archive-url=https://web.archive.org/web/20211014223318/https://www.iea.org/topics/buildings|url-status=live}}</ref> To heat buildings, alternatives to burning fossil fuels and biomass include electrification through [[heat pumps]] or [[Electric resistance heater|electric heaters]], [[Geothermal heating|geothermal energy]], [[central solar heating]], reuse of [[waste heat]], and [[seasonal thermal energy storage]].<ref>{{Cite journal|last1=Mortensen|first1=Anders Winther|last2=Mathiesen|first2=Brian Vad|last3=Hansen|first3=Anders Bavnhøj|last4=Pedersen|first4=Sigurd Lauge|last5=Grandal|first5=Rune Duban|last6=Wenzel|first6=Henrik|display-authors=4|date=2020|title=The role of electrification and hydrogen in breaking the biomass bottleneck of the renewable energy system – A study on the Danish energy system|journal=[[Applied Energy]]|volume=275|pages=115331|doi=10.1016/j.apenergy.2020.115331|issn=0306-2619|doi-access=free|bibcode=2020ApEn..27515331M |url=https://findresearcher.sdu.dk/ws/files/172072129/1_s2.0_S0306261920308436_main.pdf}}</ref><ref name=":12">{{Cite journal|last1=Knobloch|first1=Florian|last2=Pollitt|first2=Hector|last3=Chewpreecha|first3=Unnada|last4=Daioglou|first4=Vassilis|last5=Mercure|first5=Jean-Francois |display-authors=4|date=2019|title=Simulating the deep decarbonisation of residential heating for limiting global warming to 1.5&nbsp;°C|journal=[[Energy Efficiency (journal)|Energy Efficiency]] |volume=12|issue=2|pages=521–550|doi=10.1007/s12053-018-9710-0|issn=1570-6478|doi-access=free|s2cid=52830709|url=https://dspace.library.uu.nl/bitstream/handle/1874/375922/Knobloch2019_Article_SimulatingTheDeepDecarbonisati.pdf?sequence=1&isAllowed=y}}</ref><ref>{{Cite journal|last1=Alva|first1=Guruprasad|last2=Lin|first2=Yaxue|last3=Fang|first3=Guiyin|date=2018|title=An overview of thermal energy storage systems|url=http://www.sciencedirect.com/science/article/pii/S036054421732056X|url-status=live|journal=[[Energy (journal)|Energy]]|volume=144|pages=341–378|doi=10.1016/j.energy.2017.12.037|issn=0360-5442|access-date=28 November 2020|archive-date=17 July 2021|archive-url=https://web.archive.org/web/20210717132734/https://www.sciencedirect.com/science/article/abs/pii/S036054421732056X}}</ref> Heat pumps provide both heat and air conditioning through a single appliance.<ref>{{Cite news|last=Plumer|first=Brad|date=30 June 2021|title=Are 'Heat Pumps' the Answer to Heat Waves? Some Cities Think So.|work=[[The New York Times]]|url=https://www.nytimes.com/2021/06/30/climate/heat-pumps-climate.html|access-date=11 September 2021|issn=0362-4331|archive-date=10 September 2021|archive-url=https://web.archive.org/web/20210910154532/https://www.nytimes.com/2021/06/30/climate/heat-pumps-climate.html|url-status=live}}</ref> The IEA estimates heat pumps could provide over 90% of space and water heating requirements globally.<ref>{{cite web|last1=Abergel|first1=Thibaut|date=June 2020|title=Heat Pumps|url=https://www.iea.org/reports/heat-pumps|url-status=live|archive-url=https://web.archive.org/web/20210303162213/https://www.iea.org/reports/heat-pumps|archive-date=3 March 2021|access-date=12 April 2021|publisher=[[International Energy Agency|IEA]]}}</ref>   

A highly efficient way to heat buildings is through [[district heating]], in which heat is generated in a centralised location and then distributed to multiple buildings through [[insulated pipe]]s. Traditionally, most district heating systems have used fossil fuels, but [[District heating#Fourth generation|modern]] and [[cold district heating]] systems are designed to use high shares of renewable energy.<ref>{{Cite journal|last1=Buffa|first1=Simone|last2=Cozzini|first2=Marco|last3=D'Antoni|first3=Matteo|last4=Baratieri|first4=Marco|last5=Fedrizzi|first5=Roberto|display-authors=4|date=2019|title=5th generation district heating and cooling systems: A review of existing cases in Europe|journal=[[Renewable and Sustainable Energy Reviews]]|volume=104|pages=504–522|doi=10.1016/j.rser.2018.12.059|doi-access=free}}</ref><ref>{{Cite journal|last1=Lund|first1=Henrik|author-link=Henrik Lund (academic)|last2=Werner|first2=Sven|last3=Wiltshire|first3=Robin|last4=Svendsen|first4=Svend|last5=Thorsen|first5=Jan Eric|last6=Hvelplund|first6=Frede|last7=Mathiesen|first7=Brian Vad|display-authors=4|date=2014|title=4th Generation District Heating (4GDH)|url=https://linkinghub.elsevier.com/retrieve/pii/S0360544214002369|journal=[[Energy (journal)|Energy]]|volume=68|pages=1–11|doi=10.1016/j.energy.2014.02.089|access-date=13 June 2021|archive-date=7 March 2021|archive-url=https://web.archive.org/web/20210307230126/https://linkinghub.elsevier.com/retrieve/pii/S0360544214002369|url-status=live}}</ref> 

Cooling of buildings can be made more efficient through [[Passive solar building design|passive building design]], planning that minimises the [[urban heat island]] effect, and [[district cooling]] systems that cool multiple buildings with piped cold water.<ref>{{Cite web|publisher=[[United Nations Environment Programme]]|date=22 July 2020|title=How cities are using nature to keep heatwaves at bay|url=https://www.unep.org/news-and-stories/story/how-cities-are-using-nature-keep-heatwaves-bay|url-status=live|access-date=11 September 2021|ref=none|archive-date=11 September 2021|archive-url=https://web.archive.org/web/20210911225833/https://www.unep.org/news-and-stories/story/how-cities-are-using-nature-keep-heatwaves-bay}}</ref><ref name=":26">{{Cite web|date=23 May 2019|title=Four Things You Should Know About Sustainable Cooling|url=https://www.worldbank.org/en/news/feature/2019/05/23/four-things-you-should-know-about-sustainable-cooling|url-status=live|access-date=11 September 2021|publisher=[[World Bank]]|archive-date=11 September 2021|archive-url=https://web.archive.org/web/20210911232205/https://www.worldbank.org/en/news/feature/2019/05/23/four-things-you-should-know-about-sustainable-cooling}}</ref> [[Air conditioning]] requires large amounts of electricity and is not always affordable for poorer households.<ref name=":26" /> Some air conditioning units still use [[refrigerant]]s that are greenhouse gases, as some countries have not ratified the [[Kigali Amendment]] to only use climate-friendly refrigerants.<ref>{{Cite journal|last1=Mastrucci|first1=Alessio|last2=Byers|first2=Edward|last3=Pachauri|first3=Shonali|last4=Rao|first4=Narasimha D.|date=2019|title=Improving the SDG energy poverty targets: Residential cooling needs in the Global South|journal=[[Energy and Buildings]]|volume=186|pages=405–415|doi=10.1016/j.enbuild.2019.01.015|issn=0378-7788|doi-access=free|url=http://pure.iiasa.ac.at/id/eprint/15739/1/1-s2.0-S0378778818323958-main.pdf}}</ref>  

In developing countries where populations suffer from [[energy poverty]], polluting fuels such as wood or animal dung are often used for cooking. Cooking with these fuels is generally unsustainable, because they release harmful smoke and because harvesting wood can lead to forest degradation.<ref>{{Cite report|author1=[[World Health Organization]] |author2=[[International Energy Agency]] |author3=[[Global Alliance for Clean Cookstoves]] |author4=[[United Nations Development Programme]] |author5=Energising Development |name-list-style=and |author6=[[World Bank]] |date=2018|title=Accelerating SDG 7 Achievement Policy Brief 02: Achieving Universal Access to Clean and Modern Cooking Fuels, Technologies and Services|publisher=[[United Nations]]|url=https://sustainabledevelopment.un.org/content/documents/17465PB2.pdf|url-status=live|archive-url=https://web.archive.org/web/20210318023046/https://sustainabledevelopment.un.org/content/documents/17465PB2.pdf|archive-date=18 March 2021|page=3}}</ref> The universal adoption of clean cooking facilities, which are already ubiquitous in rich countries,{{sfn|Smith|Pillarisetti|2017|pp=145–146}} would dramatically improve health and have minimal negative effects on climate.{{sfn|World Health Organization|2016|p=75}}{{sfn|IPCC|2014|p=29}} Clean cooking facilities, e.g. cooking facilities that produce less indoor soot, typically use natural gas, [[liquefied petroleum gas]] (both of which consume oxygen and produce carbon-dioxide) or electricity as the energy source; biogas systems are a promising alternative in some contexts.{{sfn|Smith|Pillarisetti|2017|pp=145–146}} [[Improved cookstoves]] that burn biomass more efficiently than traditional stoves are an interim solution where transitioning to clean cooking systems is difficult.{{sfn|World Health Organization|2016|p=12}}

====Industry====
Over one-third of energy use is by industry. Most of that energy is deployed in thermal processes: generating heat, drying, and [[refrigeration]]. The share of renewable energy in industry was 14.5% in 2017—mostly low-temperature heat supplied by bioenergy and electricity. The most energy-intensive activities in industry have the lowest shares of renewable energy, as they face limitations in generating heat at temperatures over {{convert|200|C|sigfig=2}}.{{Sfn|REN21|2020|p=40}}

For some industrial processes, commercialisation of technologies that have not yet been built or operated at full scale will be needed to eliminate greenhouse gas emissions.{{Sfn|IEA|2020|p=135}} [[Steelmaking]], for instance, is difficult to electrify because it traditionally uses [[Coke (fuel)|coke]], which is derived from coal, both to create very high-temperature heat and as an ingredient in the steel itself.{{sfn|United Nations Environment Programme|2019|p=50}} The production of plastic, cement, and fertilisers also requires significant amounts of energy, with limited possibilities available to decarbonise.<ref>{{Cite journal|last1=Åhman|first1=Max|last2=Nilsson|first2=Lars J.|last3=Johansson|first3=Bengt|date=2017|title=Global climate policy and deep decarbonization of energy-intensive industries|journal=[[Climate Policy (journal)|Climate Policy]]|volume=17|issue=5|pages=634–649|doi=10.1080/14693062.2016.1167009|issn=1469-3062|doi-access=free|bibcode=2017CliPo..17..634A }}</ref> A switch to a [[circular economy]] would make industry more sustainable as it involves recycling more and thereby using less energy compared to investing energy to mine and refine new [[raw materials]].{{sfn|United Nations Environment Programme|2019|p=xxiii}}

==Government policies==
{{Further|Politics of climate change|Energy policy}}
{{quote box
| halign = left
| quote = "Bringing new energy technologies to market can often take several decades, but the imperative of reaching net‐zero emissions globally by 2050 means that progress has to be much faster. Experience has shown that the role of government is crucial in shortening the time needed to bring new technology to market and to diffuse it widely."
| author = [[International Energy Agency]] (2021){{sfn|IEA|2021|p=186}}
| width = 25%
}}
Well-designed government policies that promote energy system transformation can lower greenhouse gas emissions and improve air quality simultaneously, and in many cases can also increase energy security and lessen the financial burden of using energy.{{sfn|United Nations Environment Programme|2019|pp=39–45}} 

[[Environmental regulations]] have been used since the 1970s to promote more sustainable use of energy.{{sfn|Jaccard|2020|loc=[https://www.cambridge.org/core/books/citizens-guide-to-climate-success/we-must-price-carbon-emissions/66AEBB8BE9A7F7760DC1BCE3A9C50748 Chapter 6 – We Must Price Carbon Emissions"]|p=109}} Some governments have committed to dates for [[Coal phase-out|phasing out coal-fired power plants]] and ending new [[fossil fuel exploration]]. Governments can require that new cars produce zero emissions, or new buildings are heated by electricity instead of gas.{{sfn|United Nations Environment Programme|2019|pp=28–36}} [[Renewable portfolio standard]]s in several countries require utilities to increase the percentage of electricity they generate from renewable sources.<ref>{{cite web|last=Ciucci|first=M.|date=February 2020|title=Renewable Energy|url=https://www.europarl.europa.eu/factsheets/en/sheet/70/renewable-energy|url-status=live|archive-url=https://web.archive.org/web/20200604182037/https://www.europarl.europa.eu/factsheets/en/sheet/70/renewable-energy|archive-date=4 June 2020|access-date=3 June 2020|publisher=[[European Parliament]]|ref={{harvid|European Parliament, February|2020}}}}</ref><ref>{{cite web|date=17 April 2020|title=State Renewable Portfolio Standards and Goals|url=https://www.ncsl.org/research/energy/renewable-portfolio-standards.aspx|url-status=live|archive-url=https://web.archive.org/web/20200603174312/https://www.ncsl.org/research/energy/renewable-portfolio-standards.aspx|archive-date=3 June 2020|access-date=3 June 2020|publisher=[[National Conference of State Legislators]]|ref={{harvid|National Conference of State Legislators, 17 April|2020}}}}</ref>

Governments can accelerate energy system transformation by leading the development of infrastructure such as long-distance electrical transmission lines, smart grids, and hydrogen pipelines.{{sfn|IEA|2021|pp=14–25}}  In transport, appropriate infrastructure and incentives can make travel more efficient and less car-dependent.{{sfn|United Nations Environment Programme|2019|pp=39–45}} [[Urban planning]] that discourages [[Urban sprawl|sprawl]] can reduce energy use in local transport and buildings while enhancing quality of life.{{sfn|United Nations Environment Programme|2019|pp=39–45}} Government-funded research, procurement, and incentive policies have historically been critical to the development and maturation of clean energy technologies, such as solar and lithium batteries.{{sfn|IEA|2021|pp=184–187}} In the IEA's scenario for a net zero-emission energy system by 2050, public funding is rapidly mobilised to bring a range of newer technologies to the demonstration phase and to encourage deployment.{{sfn|IEA|2021|p=16}}

[[File:MicrocityCarSharingHangzhou.jpg|thumb|alt=Photograph of a row of cars plugged into squat metal boxes under a roof| Several countries and the European Union have committed to dates for all new cars to be [[zero-emissions vehicle]]s.{{sfn|United Nations Environment Programme|2019|pp=28–36}}]]
[[Carbon pricing]] (such as a tax on {{CO2}} emissions) gives industries and consumers an incentive to reduce emissions while letting them choose how to do so. For example, they can shift to low-emission energy sources, improve energy efficiency, or reduce their use of energy-intensive products and services.{{sfn|Jaccard|2020|pp=106–109|loc=[https://www.cambridge.org/core/books/citizens-guide-to-climate-success/we-must-price-carbon-emissions/66AEBB8BE9A7F7760DC1BCE3A9C50748 Chapter 6 – "We Must Price Carbon Emissions"]}} Carbon pricing has encountered strong [[Politics of climate change|political pushback]] in some jurisdictions, whereas energy-specific policies tend to be politically safer.<ref name="Plumer">{{Cite news|last=Plumer|first=Brad|date=8 October 2018|title=New U.N. Climate Report Says Put a High Price on Carbon |work=[[The New York Times]]|issn=0362-4331 |url=https://www.nytimes.com/2018/10/08/climate/carbon-tax-united-nations-report-nordhaus.html|access-date=4 October 2019|url-status=live|archive-date=27 September 2019 |archive-url=https://web.archive.org/web/20190927002827/https://www.nytimes.com/2018/10/08/climate/carbon-tax-united-nations-report-nordhaus.html}}</ref><ref>{{Cite journal|last=Green|first=Jessica F.|date=2021 |title=Does carbon pricing reduce emissions? A review of ex-post analyses |journal=[[Environmental Research Letters]]|volume=16|issue=4|pages=043004|doi=10.1088/1748-9326/abdae9|bibcode=2021ERL....16d3004G |s2cid=234254992|issn=1748-9326|doi-access=free}}</ref> Most studies indicate that to limit global warming to 1.5{{Nbsp}}°C, carbon pricing would need to be complemented by stringent energy-specific policies.{{sfn|IPCC|2018|loc=2.5.2.1}} As of 2019, the price of carbon in most regions is too low to achieve the goals of the Paris Agreement.<ref>
{{cite report |ref={{harvid|World Bank, June|2019}} |title=State and Trends of Carbon Pricing 2019 |url=http://documents.worldbank.org/curated/en/191801559846379845/pdf/State-and-Trends-of-Carbon-Pricing-2019.pdf |date=June 2019 |publisher=[[World Bank]] |doi=10.1596/978-1-4648-1435-8 |hdl=10986/29687 |hdl-access=free |archive-date=6 May 2020 |archive-url=https://web.archive.org/web/20200506210943/http://documents.worldbank.org/curated/en/191801559846379845/pdf/State-and-Trends-of-Carbon-Pricing-2019.pdf |url-status=live|pages=8–11 |isbn=978-1-4648-1435-8 }}
</ref> [[Carbon tax]]es provide a source of revenue that can be used to lower other taxes<ref>{{Cite web|last=|first=|date=|title=Revenue-Neutral Carbon Tax {{!}} Canada|url=https://unfccc.int/climate-action/momentum-for-change/financing-for-climate-friendly/revenue-neutral-carbon-tax|url-status=live |archive-url=https://web.archive.org/web/20191028052504/https://unfccc.int/climate-action/momentum-for-change/financing-for-climate-friendly/revenue-neutral-carbon-tax|archive-date=28 October 2019|access-date=28 October 2019|publisher=[[United Nations Framework Convention on Climate Change]]}}</ref> or help lower-income households afford higher energy costs.<ref>{{Cite news |last=Carr|first=Mathew|date=10 October 2018|title=How High Does Carbon Need to Be? Somewhere From $20–$27,000|work=[[Bloomberg News|Bloomberg]] |url=https://www.bloomberg.com/news/articles/2018-10-10/how-much-does-carbon-need-to-cost-somewhere-from-20-to-27-000|url-status=live|access-date=4 October 2019|archive-date=5 August 2019|archive-url=https://web.archive.org/web/20190805224854/https://www.bloomberg.com/news/articles/2018-10-10/how-much-does-carbon-need-to-cost-somewhere-from-20-to-27-000}}</ref> Some governments, such as the EU and the UK, are exploring the use of [[carbon border adjustments]].<ref>{{Cite web|title=EAC launches new inquiry weighing up carbon border tax measures |date=24 September 2021|publisher=[[UK Parliament]] |url=https://committees.parliament.uk/committee/62/environmental-audit-committee/news/157728/eac-launches-new-inquiry-weighing-up-carbon-border-tax-measures/|access-date=14 October 2021|archive-date=24 September 2021|archive-url=https://web.archive.org/web/20210924120030/https://committees.parliament.uk/committee/62/environmental-audit-committee/news/157728/eac-launches-new-inquiry-weighing-up-carbon-border-tax-measures/|url-status=live}}</ref> These place [[tariff]]s on imports from countries with less stringent climate policies, to ensure that industries subject to internal carbon prices remain competitive.<ref>{{Cite news|last=Plumer |first=Brad|date=14 July 2021|title=Europe Is Proposing a Border Carbon Tax. What Is It and How Will It Work?|work=[[The New York Times]]|url=https://www.nytimes.com/2021/07/14/climate/carbon-border-tax.html|access-date=10 September 2021 |issn=0362-4331|archive-date=10 September 2021|archive-url=https://web.archive.org/web/20210910225727/https://www.nytimes.com/2021/07/14/climate/carbon-border-tax.html|url-status=live}}</ref><ref>{{Cite news|last=Bharti |first=Bianca|date=12 August 2021|title=Taxing imports of heavy carbon emitters is gaining momentum – and it could hurt Canadian industry: Report|work=[[Financial Post]]|url=https://financialpost.com/news/economy/border-carbon-adjustments-canada-eu-import-carbon-tax|access-date=3 October 2021|archive-date=3 October 2021|archive-url=https://web.archive.org/web/20211003181112/https://financialpost.com/news/economy/border-carbon-adjustments-canada-eu-import-carbon-tax|url-status=live}}</ref> 

The scale and pace of policy reforms that have been initiated as of 2020 are far less than needed to fulfil the climate goals of the Paris Agreement.{{sfn|United Nations Environment Programme|2020|p=vii}}{{sfn|IEA|2021|p=13}} In addition to domestic policies, greater international cooperation is required to accelerate innovation and to assist poorer countries in establishing a sustainable path to full energy access.{{sfn|IEA|2021|pp=14–18}}

Countries may support renewables to create jobs.{{Sfn|IRENA|IEA|REN21|2018|p=19}} The [[International Labour Organization]] estimates that efforts to limit global warming to 2&nbsp;°C would result in net job creation in most sectors of the economy.<ref name=":21">{{Cite web|date=14 May 2018|title=24&nbsp;million jobs to open up in the green economy|url=http://www.ilo.org/global/about-the-ilo/newsroom/news/WCMS_628644/lang--en/index.htm|url-status=live|archive-url=https://web.archive.org/web/20210602213559/http://www.ilo.org/global/about-the-ilo/newsroom/news/WCMS_628644/lang--en/index.htm|archive-date=2 June 2021|access-date=30 May 2021|publisher=[[International Labour Organization]]}}</ref> It predicts that 24&nbsp;million new jobs would be created by 2030 in areas such as renewable electricity generation, improving energy-efficiency in buildings, and the transition to electric vehicles. Six million jobs would be lost, in sectors such as mining and fossil fuels.<ref name=":21" /> Governments can make the transition to sustainable energy more politically and socially feasible by ensuring a [[just transition]] for workers and regions that depend on the fossil fuel industry, to ensure they have alternative economic opportunities.{{sfn|United Nations Environment Programme|2019|pp=46–55}}

==Finance==
{{Further|Climate finance}}
[[File:20210119 Renewable energy investment - 2004- BloombergNEF.svg |thumb|upright=1.35|alt=Graph of global investment for renewable energy, electrified heat and transport, and other non-fossil-fuel energy sources |Electrified transport and renewable energy are key areas of investment for the [[renewable energy transition]].<ref name=BloombergNEF_20230126>{{cite news |last1=Catsaros |first1=Oktavia |title=Global Low-Carbon Energy Technology Investment Surges Past $1 Trillion for the First Time |url=https://about.bnef.com/blog/global-low-carbon-energy-technology-investment-surges-past-1-trillion-for-the-first-time/ |publisher=Bloomberg NEF (New Energy Finance) |date=26 January 2023 |archive-url=https://web.archive.org/web/20230522001857/https://about.bnef.com/blog/global-low-carbon-energy-technology-investment-surges-past-1-trillion-for-the-first-time/ |archive-date=22 May 2023 |at=Figure 1 |quote=Defying supply chain disruptions and macroeconomic headwinds, 2022 energy transition investment jumped 31% to draw level with fossil fuels |url-status=live }}</ref>]]
Raising enough money for innovation and investment is a prerequisite for the energy transition.<ref name=":22">{{Cite journal|last1=Mazzucato|first1=Mariana|last2=Semieniuk|first2=Gregor|date=2018|title=Financing renewable energy: Who is financing what and why it matters|journal=[[Technological Forecasting and Social Change]]|volume=127|pages=8–22|doi=10.1016/j.techfore.2017.05.021|issn=0040-1625|doi-access=free|url=https://discovery.ucl.ac.uk/10044043/1/1-s2.0-S0040162517306820-main.pdf}}</ref> The IPCC estimates that to limit global warming to 1.5&nbsp;°C, US$2.4&nbsp;trillion would need to be invested in the energy system each year between 2016 and 2035. Most studies project that these costs, equivalent to 2.5% of world GDP, would be small compared to the economic and health benefits.{{sfn|United Nations Development Programme|United Nations Framework Convention on Climate Change|2019|page=24}} Average annual investment in low-carbon energy technologies and energy efficiency would need to be six times more by 2050 compared to 2015.{{sfn|IPCC|2018|page=96}} Underfunding is particularly acute in the least developed countries, which are not attractive to the private sector.{{Sfn|IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization|2021|pp=129, 132}} 

The [[United Nations Framework Convention on Climate Change]] estimates that climate financing totalled $681&nbsp;billion in 2016.{{sfn|United Nations Framework Convention on Climate Change|2018|p=54}} Most of this is private-sector investment in renewable energy deployment, public-sector investment in sustainable transport, and private-sector investment in energy efficiency.{{sfn|United Nations Framework Convention on Climate Change|2018|p=9}} The Paris Agreement includes a pledge of an extra $100&nbsp;billion per year from developed countries to poor countries, to do climate change mitigation and adaptation. However, this goal has not been met and measurement of progress has been hampered by unclear accounting rules.<ref>{{Cite journal|last1=Roberts|first1=J. Timmons|last2=Weikmans|first2=Romain|last3=Robinson|first3=Stacy-ann|last4=Ciplet|first4=David|last5=Khan|first5=Mizan|last6=Falzon|first6=Danielle|display-authors=4|date=2021|title=Rebooting a failed promise of climate finance|journal=[[Nature Climate Change]]|volume=11|issue=3|pages=180–182|bibcode=2021NatCC..11..180R|doi=10.1038/s41558-021-00990-2|issn=1758-6798|doi-access=free|url=https://dipot.ulb.ac.be/dspace/bitstream/2013/319545/3/Rebootingclimatefinance.pdf}}</ref><ref>{{Cite news|last=Radwanski|first=Adam|date=29 September 2021|title=Opinion: As pivotal climate summit approaches, Canada at centre of efforts to repair broken trust among poorer countries|work=[[The Globe and Mail]]|url=https://www.theglobeandmail.com/business/commentary/article-as-pivotal-climate-summit-approaches-canada-at-centre-of-efforts-to/|access-date=30 September 2021|archive-date=30 September 2021|archive-url=https://web.archive.org/web/20210930050603/https://www.theglobeandmail.com/business/commentary/article-as-pivotal-climate-summit-approaches-canada-at-centre-of-efforts-to/|url-status=live}}</ref> If energy-intensive businesses like chemicals, fertilizers, ceramics, steel, and non-ferrous metals invest significantly in R&D, its usage in industry might amount to between 5% and 20% of all energy used.<ref name=":78">{{Cite web |title=Here are the clean energy innovations that will beat climate change |url=https://www.eib.org/en/essays/green-energy-innovation |access-date=26 September 2022 |website=European Investment Bank |language=en}}</ref><ref>{{Cite web |title=Home |url=https://www.oecd-ilibrary.org/sites/5d01a32d-en/index.html?itemId=/content/component/5d01a32d-en |access-date=19 October 2022 |website=www.oecd-ilibrary.org |language=en}}</ref>

Fossil fuel funding and [[energy subsidy#Fossil fuel subsidies|subsidies]] are a significant barrier to the energy transition.<ref>{{Cite web|last1=Bridle|first1=Richard|last2=Sharma|first2=Shruti|last3=Mostafa|first3=Mostafa|last4=Geddes|first4=Anna|date=June 2019|title=Fossil Fuel to Clean Energy Subsidy Swaps: How to pay for an energy revolution|url=https://www.iisd.org/sites/default/files/publications/fossil-fuel-clean-energy-subsidy-swap.pdf|url-status=live|archive-url=https://web.archive.org/web/20191117055218/https://www.iisd.org/sites/default/files/publications/fossil-fuel-clean-energy-subsidy-swap.pdf|archive-date=17 November 2019|access-date=|publisher=[[International Institute for Sustainable Development]]|page=iv}}</ref><ref name=":22" /> Direct global fossil fuel subsidies were $319&nbsp;billion in 2017. This rises to $5.2&nbsp;trillion when indirect costs are priced in, like the effects of air pollution.<ref name="Watts_et_al_2019">{{cite journal|last1=Watts|first1=N.|last2=Amann|first2=M.|last3=Arnell|first3=N.|last4=Ayeb-Karlsson|first4=S.|display-authors=etal|year=2019|title=The 2019 report of The Lancet Countdown on health and climate change: ensuring that the health of a child born today is not defined by a changing climate.|url=http://sro.sussex.ac.uk/id/eprint/88053/4/__smbhome.uscs.susx.ac.uk_tjk30_Documents_The%202019%20Report%20of%20the%20Lancet%20Countdown%20-%20revised.pdf|journal=[[The Lancet]]|volume=394|issue=10211|pages=1836–1878|doi=10.1016/S0140-6736(19)32596-6|pmid=31733928|s2cid=207976337|access-date=3 November 2021|url-access=}}</ref> Ending these could lead to a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths.{{Sfn|United Nations Development Programme|2020|page=10}} Funding for clean energy has been largely unaffected by the [[COVID-19 pandemic]], and pandemic-related economic stimulus packages offer possibilities for a [[green recovery]].<ref>{{Cite journal|last1=Kuzemko|first1=Caroline|last2=Bradshaw|first2=Michael|last3=Bridge|first3=Gavin|last4=Goldthau|first4=Andreas|last5=Jewell|first5=Jessica|display-authors=4|date=2020|title=Covid-19 and the politics of sustainable energy transitions|url=|journal=[[Energy Research & Social Science]]|volume=68|pages=101685|doi=10.1016/j.erss.2020.101685|issn=2214-6296|pmc=7330551|pmid=32839704}}</ref>{{Sfn|IRENA|2021|p=5}}

==References==

{{Reflist}}

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{{refend}}

==External links==
{{Spoken Wikipedia|date=10 January 2022|En-Sustainable_energy-article.ogg}}

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*'''''<small>{{portal-inline|Renewable energy}}</small>'''''
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{{DEFAULTSORT:Sustainable Energy}}
[[Category:Sustainable energy| ]]
[[Category:Climate change mitigation]]
[[Category:Climate change policy]]
[[Category:Emissions reduction]]
[[Category:Energy economics]]
[[Category:Environmental impact of the energy industry]]
[[Category:Sustainable development]]