Sustainable energy

"Green power" redirects here. For other uses, see Green power (disambiguation).

Sustainable energy examples: Concentrated solar power with molten salt heat storage in Spain; wind energy in South Africa; electrified public transport in Singapore; and clean cooking in Ethiopia.

Energy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs."<ref name="FOOTNOTEKutscherMilfordKreith20195–6">Kutscher, Milford & Kreith 2019, pp. 5–6.</ref><ref>Zhang, Wei; Li, Binshuai; Xue, Rui; Wang, Chengcheng; Cao, Wei (2021). "A systematic bibliometric review of clean energy transition: Implications for low-carbon development". PLOS ONE. 16 (12): e0261091. Bibcode:2021PLoSO..1661091Z. doi:10.1371/journal.pone.0261091. PMC 8641874. PMID 34860855.</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, hydroelectric power, 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 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 accidents. Switching from coal to natural gas has environmental benefits, including a lower 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 fuels provide 85% of the world's energy consumption, and the energy system is responsible for 76% of global greenhouse gas emissions. Around 790 million people in developing countries lack access to electricity, and 2.6 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 million deaths each year. Therefore, the transition to a low-carbon energy system would have strong 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 2 °C (3.6 °F). These pathways include phasing out coal-fired power plants, producing more electricity from clean sources such as wind and solar, and shifting towards using 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 hydrogen fuel produced from low-emission energy sources. To accommodate larger shares of variable renewable energy, electrical grids require flexibility through infrastructure such as 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 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 1.5 °C (2.7 °F). 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 pricing, renewable portfolio standards, 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.

Definitions and background

"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."

UN Secretary-General Ban Ki-moon<ref name="FOOTNOTEUnited Nations Development Programme20165">United Nations Development Programme 2016, p. 5.</ref>

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".<ref name="FOOTNOTEKutscherMilfordKreith20195–6">Kutscher, Milford & Kreith 2019, pp. 5–6.</ref> This description of sustainable development has since been referenced in many definitions and explanations of sustainable energy.<ref name="FOOTNOTEKutscherMilfordKreith20195–6">Kutscher, Milford & Kreith 2019, pp. 5–6.</ref><ref name=":OU">"Definitions: energy, sustainability and the future". The Open University. Archived from the original on 27 January 2021. Retrieved 30 December 2020.</ref><ref name="FOOTNOTEGolus̆inPopovDodić20138">Golus̆in, Popov & Dodić 2013, p. 8.</ref><ref name=":Galarraga">Template:Citec</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>Gunnarsdottir, I.; Davidsdottir, B.; Worrel, E.; Sigurgeirsdottir, S. (2021). "Sustainable energy development: History of the concept and emerging themes". Renewable and Sustainable Energy Reviews. 141: 110770. doi:10.1016/j.rser.2021.110770. ISSN 1364-0321. S2CID 233585148. Archived from the original on 15 August 2021. Retrieved 15 August 2021.</ref>

The environmental dimension of sustainability includes greenhouse gas emissions, impacts on biodiversity and ecosystems, hazardous waste and toxic emissions,<ref name=":ECE">UNECE 2020, pp. 3–4</ref> water consumption,<ref name="FOOTNOTEKutscherMilfordKreith20191–2">Kutscher, Milford & Kreith 2019, pp. 1–2.</ref> 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>Vera, Ivan; Langlois, Lucille (2007). "Energy indicators for sustainable development". Energy. 32 (6): 875–882. doi:10.1016/j.energy.2006.08.006. ISSN 0360-5442. Archived from the original on 15 August 2021. Retrieved 15 August 2021.</ref><ref name="FOOTNOTEKutscherMilfordKreith20193–5">Kutscher, Milford & Kreith 2019, pp. 3–5.</ref> Social issues include access to affordable and reliable energy for all people, workers' rights, and land rights.<ref name=":Galarraga" /><ref name=":ECE" />

Environmental impacts

A woman in rural Rajasthan, India, collects firewood. The use of wood and other polluting fuels for cooking causes millions of deaths each year from 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.<ref name="FOOTNOTEUnited Nations Environment Programme201946">United Nations Environment Programme 2019, p. 46.</ref> Energy production and consumption are responsible for 76% of annual human-caused greenhouse gas emissions as of 2018.<ref name=":23">"Global Historical Emissions". Climate Watch. Archived from the original on 4 June 2021. Retrieved 19 August 2021.</ref><ref>Ge, Mengpin; Friedrich, Johannes; Vigna, Leandro (August 2021). "4 Charts Explain Greenhouse Gas Emissions by Countries and Sectors". World Resources Institute. Archived from the original on 19 August 2021. Retrieved 19 August 2021.</ref> The 2015 international Paris Agreement on climate change aims to limit global warming to well below 2 °C (3.6 °F) and preferably to 1.5 °C (2.7 °F); achieving this goal will require that emissions be reduced as soon as possible and reach net-zero by mid-century.<ref>"The Paris Agreement". United Nations Framework Convention on Climate Change. Archived from the original on 19 March 2021. Retrieved 18 September 2021.</ref>

The burning of fossil fuels and biomass is a major source of air pollution,<ref>Watts, Nick; Amann, Markus; Arnell, Nigel; Ayeb-Karlsson, Sonja; et al. (2021). "The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises" (PDF). The Lancet. 397 (10269): 151. doi:10.1016/S0140-6736(20)32290-X. ISSN 0140-6736. PMID 33278353.</ref><ref>"Every breath you take: The staggering, true cost of air pollution". United Nations Development Programme. 4 June 2019. Archived from the original on 20 April 2021. Retrieved 4 May 2021.</ref> which causes an estimated 7 million deaths each year, with the greatest attributable disease burden seen in low and middle-income countries.<ref>"New WHO Global Air Quality Guidelines aim to save millions of lives from air pollution". World Health Organization. 22 September 2021. Archived from the original on 23 September 2021. Retrieved 16 October 2021.</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>"Acid Rain and Water". United States Geological Survey. Archived from the original on 27 June 2021. Retrieved 14 October 2021.</ref> Air pollution is the second-leading cause of death from non-infectious disease.<ref name="FOOTNOTEWorld Health Organization201816">World Health Organization 2018, p. 16.</ref> An estimated 99% of the world's population lives with levels of air pollution that exceed the World Health Organization recommended limits.<ref>"Ambient (outdoor) air pollution". World Health Organization. 22 September 2021. Archived from the original on 8 October 2021. Retrieved 22 October 2021.</ref>

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 million deaths annually,<ref>Ritchie, Hannah; Roser, Max (2019). "Access to Energy". Our World in Data. Archived from the original on 1 April 2021. Retrieved 1 April 2021.</ref><ref name="FOOTNOTEWorld Health Organization201816">World Health Organization 2018, p. 16.</ref> and also contributes significantly to outdoor air pollution.<ref name="FOOTNOTEWorld Health Organization2016vii–xiv">World Health Organization 2016, pp. vii–xiv.</ref> Health effects are concentrated among women, who are likely to be responsible for cooking, and young children.<ref name="FOOTNOTEWorld Health Organization2016vii–xiv">World Health Organization 2016, pp. vii–xiv.</ref>

Environmental impacts extend beyond the by-products of combustion. Oil spills at sea harm marine life and may cause fires which release toxic emissions.<ref name="FOOTNOTESoysalSoysal2020118">Soysal & Soysal 2020, p. 118.</ref> 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.<ref name="FOOTNOTESoysalSoysal2020470–472">Soysal & Soysal 2020, pp. 470–472.</ref> Excessive harvesting of wood and other combustible material for burning can cause serious local environmental damage, including desertification.<ref name="FOOTNOTETester2012504">Tester 2012, p. 504.</ref>

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">Life Cycle Assessment of Electricity Generation Options (Report). United Nations Economic Commission for Europe. p. 59. Archived from the original on 15 November 2021. Retrieved 24 November 2021.</ref>

Sustainable development goals

Further information: Energy poverty and Energy poverty and cooking

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>Kessides, Ioannis N.; Toman, Michael (28 July 2011). "The Global Energy Challenge". World Bank. Archived from the original on 25 July 2019. Retrieved 27 September 2019.</ref> Reliable and affordable energy, particularly electricity, is essential for health care, education, and economic development.<ref name="FOOTNOTEMorrisMensah-KutinGreeneDiam-valla201524–27">Morris et al. 2015, pp. 24–27.</ref> As of 2020, 790 million people in developing countries do not have access to electricity, and around 2.6 billion rely on burning polluting fuels for cooking.<ref name=":3">"Access to clean cooking". SDG7: Data and Projections. IEA. October 2020. Archived from the original on 6 December 2019. Retrieved 31 March 2021.</ref><ref name="FOOTNOTEIEA2021167">IEA 2021, p. 167.</ref>

Improving energy access in the least-developed countries and making energy cleaner are key to achieving most of the United Nations 2030 Sustainable Development Goals,<ref>Sarkodie, Samuel Asumadu (20 July 2022). "Winners and losers of energy sustainability—Global assessment of the Sustainable Development Goals". Science of the Total Environment. 831. 154945. Bibcode:2022ScTEn.831o4945S. doi:10.1016/j.scitotenv.2022.154945. hdl:11250/3023660. ISSN 0048-9697. PMID 35367559. S2CID 247881708.</ref> which cover issues ranging from climate action to gender equality.<ref name="Welcome to the United Nations 2018">Deputy Secretary-General (6 June 2018). "Sustainable Development Goal 7 on Reliable, Modern Energy 'Golden Thread' Linking All Other Targets, Deputy-Secretary-General Tells High-Level Panel" (Press release). United Nations. Archived from the original on 17 May 2021. Retrieved 19 March 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 facilities by 2030.<ref name=":5">"Goal 7: Ensure access to affordable, reliable, sustainable and modern energy for all". SDG Tracker. Archived from the original on 2 February 2021. Retrieved 12 March 2021.</ref>

Energy conservation

Main articles: Energy conservation and Efficient energy use

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>"Energy use per person". Our World in Data. Archived from the original on 28 November 2020. Retrieved 16 July 2021.</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>"Europe 2030: Energy saving to become "first fuel"". EU Science Hub. European Commission. 25 February 2016. Archived from the original on 18 September 2021. Retrieved 18 September 2021.</ref><ref>Motherway, Brian (19 December 2019). "Energy efficiency is the first fuel, and demand for it needs to grow". IEA. Archived from the original on 18 September 2021. Retrieved 18 September 2021.</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>"Energy Efficiency 2018: Analysis and outlooks to 2040". IEA. October 2018. Archived from the original on 29 September 2020.</ref>

Energy can be conserved by increasing the technical efficiency of appliances, vehicles, industrial processes, and buildings.<ref>Fernandez Pales, Araceli; Bouckaert, Stéphanie; Abergel, Thibaut; Goodson, Timothy (10 June 2021). "Net zero by 2050 hinges on a global push to increase energy efficiency". IEA. Archived from the original on 20 July 2021. Retrieved 19 July 2021.</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.<ref name="FOOTNOTEIEA202168–69">IEA 2021, pp. 68–69.</ref> Government policies to improve efficiency can include building codes, performance standards, carbon pricing, and the development of energy-efficient infrastructure to encourage changes in transport modes.<ref name="FOOTNOTEIEA202168–69">IEA 2021, pp. 68–69.</ref><ref>Mundaca, Luis; Ürge-Vorsatz, Diana; Wilson, Charlie (2019). "Demand-side approaches for limiting global warming to 1.5 °C" (PDF). Energy Efficiency. 12 (2): 343–362. doi:10.1007/s12053-018-9722-9. ISSN 1570-6478. 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.<ref name="FOOTNOTEIEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization202112">IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization 2021, p. 12.</ref> In 2010, global energy intensity was 5.6 megajoules (1.6 kWh) per US dollar of GDP.<ref name="FOOTNOTEIEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization202112">IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization 2021, p. 12.</ref> United Nations goals call for energy intensity to decrease by 2.6% each year between 2010 and 2030.<ref name="FOOTNOTEIEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization202111">IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization 2021, p. 11.</ref> In recent years this target has not been met. For instance, between 2017 and 2018, energy intensity decreased by only 1.1%.<ref name="FOOTNOTEIEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization202111">IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization 2021, p. 11.</ref> Efficiency improvements often lead to a rebound effect in which consumers use the money they save to buy more energy-intensive goods and services.<ref>Brockway, Paul; Sorrell, Steve; Semieniuk, Gregor; Heun, Matthew K.; et al. (2021). "Energy efficiency and economy-wide rebound effects: A review of the evidence and its implications" (PDF). Renewable and Sustainable Energy Reviews. 141: 110781. doi:10.1016/j.rser.2021.110781. ISSN 1364-0321. S2CID 233554220.</ref> For example, recent technical efficiency improvements in transport and buildings have been largely offset by trends in consumer behaviour, such as selecting larger vehicles and homes.<ref name=":6">"Energy Efficiency 2019". IEA. November 2019. Archived from the original on 13 October 2020. Retrieved 21 September 2020.</ref>

Sustainable energy sources

Renewable energy sources

Main article: Renewable energy

In 2023, electricity generation from wind and solar sources was projected to exceed 30% by 2030.<ref name=RMI_20230613>Bond, Kingsmill; Butler-Sloss, Sam; Lovins, Amory; Speelman, Laurens; Topping, Nigel (13 June 2023). "Report / 2023 / X-Change: Electricity / On track for disruption". Rocky Mountain Institute. Archived from the original on 13 July 2023.</ref>

Renewable energy capacity has steadily grown, led by solar photovoltaic power.<ref name=IEA_202306>Source for data beginning in 2017: "Renewable Energy Market Update Outlook for 2023 and 2024" (PDF). IEA.org. International Energy Agency (IEA). June 2023. p. 19. Archived (PDF) from the original on 11 July 2023. IEA. CC BY 4.0. ● Source for data through 2016: "Renewable Energy Market Update / Outlook for 2021 and 2022" (PDF). IEA.org. International Energy Agency. May 2021. p. 8. Archived (PDF) from the original on 25 March 2023. IEA. Licence: CC BY 4.0</ref>

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>"World Energy Investment 2023 / Overview and key findings". International Energy Agency (IEA). 25 May 2023. Archived from the original on 31 May 2023. Global energy investment in clean energy and in fossil fuels, 2015-2023 (chart) — From pages 8 and 12 of World Energy Investment 2023 (archive).</ref>

Renewable energy sources are essential to sustainable energy, as they generally strengthen energy security and emit far fewer greenhouse gases than fossil fuels.<ref name="FOOTNOTEIEA20073">IEA 2007, p. 3.</ref> 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>Santangeli, Andrea; Toivonen, Tuuli; Pouzols, Federico Montesino; Pogson, Mark; et al. (2016). "Global change synergies and trade-offs between renewable energy and biodiversity". GCB Bioenergy. 8 (5): 941–951. Bibcode:2016GCBBi...8..941S. doi:10.1111/gcbb.12299. hdl:2164/6138. ISSN 1757-1707.</ref><ref>Rehbein, Jose A.; Watson, James E.M.; Lane, Joe L.; Sonter, Laura J.; et al. (2020). "Renewable energy development threatens many globally important biodiversity areas" (PDF). Global Change Biology. 26 (5): 3040–3051. Bibcode:2020GCBio..26.3040R. doi:10.1111/gcb.15067. ISSN 1365-2486. PMID 32133726. S2CID 212418220.</ref>

Hydropower is the largest source of renewable electricity while solar and wind energy are growing rapidly. Photovoltaic solar and onshore wind are the cheapest forms of new power generation capacity in most countries.<ref>Ritchie, Hannah (2019). "Renewable Energy". Our World in Data. Archived from the original on 4 August 2020. Retrieved 31 July 2020.</ref><ref name="IEA Renewables 2020">Renewables 2020 Analysis and forecast to 2025 (PDF) (Report). IEA. 2020. p. 12. Archived from the original on 26 April 2021.</ref> For more than half of the 770 million people who currently lack access to electricity, decentralised renewable energy such as solar-powered mini-grids is likely the cheapest method of providing it by 2030.<ref name=":1">"Access to electricity". SDG7: Data and Projections. IEA. 2020. Archived from the original on 13 May 2021. Retrieved 5 May 2021.</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">"Infrastructure Solutions: The power of purchase agreements". European Investment Bank. Retrieved 1 September 2022.</ref><ref>"Renewable Power – Analysis". IEA. Retrieved 1 September 2022.</ref><ref>"Global Electricity Review 2022". Ember. 29 March 2022. Retrieved 1 September 2022.</ref><ref>"Renewable Energy and Electricity | Sustainable Energy | Renewable Energy - World Nuclear Association". world-nuclear.org. Retrieved 1 September 2022.</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

A photovoltaic power station in California, United States

Main articles: Solar power and Solar water heating

The Sun is Earth's primary source of energy, a clean and abundantly available resource in many regions.<ref name="FOOTNOTESoysalSoysal2020406">Soysal & Soysal 2020, p. 406.</ref> In 2019, solar power provided around 3% of global electricity,<ref name=":4">"Wind & Solar Share in Electricity Production Data". Global Energy Statistical Yearbook 2021. Enerdata. Archived from the original on 19 July 2019. Retrieved 13 June 2021.</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 solar parks. Costs of solar photovoltaic cells have dropped rapidly, driving strong growth in worldwide capacity.<ref name="FOOTNOTEKutscherMilfordKreith201934–35">Kutscher, Milford & Kreith 2019, pp. 34–35.</ref> The cost of electricity from new solar farms is competitive with, or in many places, cheaper than electricity from existing coal plants.<ref name=":10">"Levelized Cost of Energy and of Storage". Lazard. 19 October 2020. Archived from the original on 25 February 2021. Retrieved 26 February 2021.</ref> Various projections of future energy use identify solar PV as one of the main sources of energy generation in a sustainable mix.<ref>Victoria, Marta; Haegel, Nancy; Peters, Ian Marius; Sinton, Ron; et al. (2021). "Solar photovoltaics is ready to power a sustainable future". Joule. 5 (5): 1041–1056. doi:10.1016/j.joule.2021.03.005. ISSN 2542-4351. OSTI 1781630.</ref><ref name="FOOTNOTEIRENA202119, 22">IRENA 2021, pp. 19, 22.</ref>

Most components of solar panels can be easily recycled, but this is not always done in the absence of regulation.<ref>Goetz, Katelyn P.; Taylor, Alexander D.; Hofstetter, Yvonne J.; Vaynzof, Yana (2020). "Sustainability in Perovskite Solar Cells". ACS Applied Materials & Interfaces. 13 (1): 1–17. doi:10.1021/acsami.0c17269. ISSN 1944-8244. PMID 33372760. S2CID 229714294.</ref> Panels typically contain heavy metals, so they pose environmental risks if put in landfills.<ref>Xu, Yan; Li, Jinhui; Tan, Quanyin; Peters, Anesia Lauren; et al. (2018). "Global status of recycling waste solar panels: A review". Waste Management. 75: 450–458. Bibcode:2018WaMan..75..450X. doi:10.1016/j.wasman.2018.01.036. ISSN 0956-053X. PMID 29472153. Archived from the original on 28 June 2021. Retrieved 28 June 2021.</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>Tian, Xueyu; Stranks, Samuel D.; You, Fengqi (2020). "Life cycle energy use and environmental implications of high-performance perovskite tandem solar cells". Science Advances. 6 (31): eabb0055. Bibcode:2020SciA....6...55T. doi:10.1126/sciadv.abb0055. ISSN 2375-2548. PMC 7399695. PMID 32937582. 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 power generation, as some of the heat is typically stored to enable electricity to be generated when needed.<ref name="FOOTNOTEKutscherMilfordKreith201935–36">Kutscher, Milford & Kreith 2019, pp. 35–36.</ref><ref>"Solar energy". International Renewable Energy Agency. Archived from the original on 13 May 2021. Retrieved 5 June 2021.</ref> In addition to electricity production, solar energy is used more directly; solar thermal heating systems are used for hot water production, heating buildings, drying, and desalination.<ref name="FOOTNOTEREN212020124">REN21 2020, p. 124.</ref>

Wind power

Main articles: Wind power and Environmental impact of wind power

Wind turbines in Xinjiang, China

Wind has been an important driver of development over millennia, providing mechanical energy for industrial processes, water pumps, and sailing ships.<ref name="FOOTNOTESoysalSoysal2020366">Soysal & Soysal 2020, p. 366.</ref> 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>"What are the advantages and disadvantages of offshore wind farms?". American Geosciences Institute. 12 May 2016. Archived from the original on 18 September 2021. Retrieved 18 September 2021.</ref>

Onshore wind farms, often built in wild or rural areas, have a visual impact on the landscape.<ref name="FOOTNOTESzarka2007176">Szarka 2007, p. 176.</ref> While collisions with wind turbines kill both bats and to a lesser extent birds, these impacts are lower than from other infrastructure such as windows and transmission lines.<ref>Wang, Shifeng; Wang, Sicong (2015). "Impacts of wind energy on environment: A review". Renewable and Sustainable Energy Reviews. 49: 437–443. doi:10.1016/j.rser.2015.04.137. ISSN 1364-0321. Archived from the original on 4 June 2021. Retrieved 15 June 2021.</ref><ref name="FOOTNOTESoysalSoysal2020215">Soysal & Soysal 2020, p. 215.</ref> 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.<ref name="FOOTNOTESoysalSoysal2020213">Soysal & Soysal 2020, p. 213.</ref> Little energy is needed for wind turbine construction compared to the energy produced by the wind power plant itself.<ref>Huang, Yu-Fong; Gan, Xing-Jia; Chiueh, Pei-Te (2017). "Life cycle assessment and net energy analysis of offshore wind power systems". Renewable Energy. 102: 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>Belton, Padraig (7 February 2020). "What happens to all the old wind turbines?". BBC. Archived from the original on 23 February 2021. Retrieved 27 February 2021.</ref>

Hydropower

Main article: Hydroelectricity

Guri Dam, a hydroelectric dam in Venezuela

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.<ref name="FOOTNOTESmil2017b286">Smil 2017b, p. 286.</ref><ref name="FOOTNOTEREN21202121">REN21 2021, p. 21.</ref>

In conventional hydropower, a reservoir is created behind a dam. Conventional hydropower plants provide a highly flexible, 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>Template:Citec</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">Template:Citec</ref> The highest emissions tend to occur with large dams in tropical regions.<ref>Almeida, Rafael M.; Shi, Qinru; Gomes-Selman, Jonathan M.; Wu, Xiaojian; et al. (2019). "Reducing greenhouse gas emissions of Amazon hydropower with strategic dam planning". Nature Communications. 10 (1): 4281. Bibcode:2019NatCo..10.4281A. doi:10.1038/s41467-019-12179-5. ISSN 2041-1723. 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">Moran, Emilio F.; Lopez, Maria Claudia; Moore, Nathan; Müller, Norbert; et al. (2018). "Sustainable hydropower in the 21st century". Proceedings of the National Academy of Sciences. 115 (47): 11891–11898. Bibcode:2018PNAS..11511891M. doi:10.1073/pnas.1809426115. ISSN 0027-8424. PMC 6255148. PMID 30397145.</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 articles: Geothermal power and Geothermal heating

Cooling towers at a geothermal power plant in Larderello, Italy

Geothermal energy is produced by tapping into deep underground heat<ref name="László 1981 248–249">László, Erika (1981). "Geothermal Energy: An Old Ally". Ambio. 10 (5): 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 (the ability of the rock to allow fluids to pass through).<ref name="FOOTNOTEREN21202097">REN21 2020, p. 97.</ref> Power is produced from the steam created in underground reservoirs.<ref>"Geothermal Energy Information and Facts". National Geographic. 19 October 2009. Archived from the original on 8 August 2021. Retrieved 8 August 2021.</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 isotopes.<ref name="FOOTNOTESoysalSoysal2020222, 228">Soysal & Soysal 2020, pp. 222, 228.</ref> 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.<ref name="FOOTNOTESoysalSoysal2020228–229">Soysal & Soysal 2020, pp. 228–229.</ref>

Bioenergy

Main article: Bioenergy

Further information: Sustainable biofuel

Kenyan dairy farmer lighting a biogas lamp. Biogas produced from biomass is a renewable energy source that can be burned for cooking or light.

A sugarcane plantation to produce ethanol in Brazil

Biomass is renewable organic material that comes from plants and animals.<ref>"Biomass explained". US Energy Information Administration. 8 June 2021. Archived from the original on 15 September 2021. Retrieved 13 September 2021.</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>Kopetz, Heinz (2013). "Build a biomass energy market". Nature. 494 (7435): 29–31. doi:10.1038/494029a. ISSN 1476-4687. PMID 23389528.</ref><ref>Demirbas, Ayhan (2008). "Biofuels sources, biofuel policy, biofuel economy and global biofuel projections". Energy Conversion and Management. 49 (8): 2106–2116. doi:10.1016/j.enconman.2008.02.020. ISSN 0196-8904. Archived from the original on 18 March 2013. Retrieved 11 February 2021.</ref>

The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown.<ref name=":0">Correa, Diego F.; Beyer, Hawthorne L.; Fargione, Joseph E.; Hill, Jason D.; et al. (2019). "Towards the implementation of sustainable biofuel production systems". Renewable and Sustainable Energy Reviews. 107: 250–263. doi:10.1016/j.rser.2019.03.005. ISSN 1364-0321. S2CID 117472901. Archived from the original on 17 July 2021. Retrieved 7 February 2021.</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>Daley, Jason (24 April 2018). "The EPA Declared That Burning Wood Is Carbon Neutral. It's Actually a Lot More Complicated". Smithsonian Magazine. Archived from the original on 30 June 2021. Retrieved 14 September 2021.</ref> However, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers.<ref name="FOOTNOTETester2012512">Tester 2012, p. 512.</ref><ref name="FOOTNOTESmil2017a162">Smil 2017a, p. 162.</ref> Approximately one-third of all wood used for traditional heating and cooking in tropical areas is harvested unsustainably.<ref name="FOOTNOTEWorld Health Organization201673">World Health Organization 2016, p. 73.</ref> 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 land-use change, cultivation, and processing can result in higher overall carbon emissions for bioenergy compared to using fossil fuels.<ref name="FOOTNOTESmil2017a162">Smil 2017a, p. 162.</ref><ref name="FOOTNOTEIPCC2014616">IPCC 2014, p. 616.</ref>

Use of farmland for growing biomass can result in less land being available for growing food. In the United States, around 10% of motor gasoline has been replaced by corn-based ethanol, which requires a significant proportion of the harvest.<ref>"Biofuels explained: Ethanol". US Energy Information Administration. 18 June 2020. Archived from the original on 14 May 2021. Retrieved 16 May 2021.</ref><ref>Foley, Jonathan (5 March 2013). "It's Time to Rethink America's Corn System". Scientific American. Archived from the original on 3 January 2020. Retrieved 16 May 2021.</ref> In Malaysia and Indonesia, clearing forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for diverse species.<ref>Ayompe, Lacour M.; Schaafsma, M.; Egoh, Benis N. (1 January 2021). "Towards sustainable palm oil production: The positive and negative impacts on ecosystem services and human wellbeing". Journal of Cleaner Production. 278: 123914. doi:10.1016/j.jclepro.2020.123914. ISSN 0959-6526. S2CID 224853908.</ref><ref>Lustgarten, Abrahm (20 November 2018). "Palm Oil Was Supposed to Help Save the Planet. Instead It Unleashed a Catastrophe". The New York Times. ISSN 0362-4331. Archived from the original on 17 May 2019. Retrieved 15 May 2019.</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.<ref name="FOOTNOTESmil2017a161">Smil 2017a, p. 161.</ref>

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, 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.<ref name="FOOTNOTENational Academies of Sciences, Engineering, and Medicine20193">National Academies of Sciences, Engineering, and Medicine 2019, p. 3.</ref>

Marine energy

Main article: Marine energy

Marine energy has the smallest share of the energy market. It includes 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.<ref name="FOOTNOTEREN212021113–116">REN21 2021, pp. 113–116.</ref>

Non-renewable energy sources

Fossil fuel switching and mitigation

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 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">"The Role of Gas: Key Findings". IEA. July 2019. Archived from the original on 1 September 2019. Retrieved 4 October 2019.</ref> Natural gas combustion also produces less air pollution than coal.<ref>"Natural gas and the environment". US Energy Information Administration. Archived from the original on 2 April 2021. Retrieved 28 March 2021.</ref> However, natural gas is a potent greenhouse gas in itself, and leaks during extraction and transportation can negate the advantages of switching away from coal.<ref name=":27">Storrow, Benjamin. "Methane Leaks Erase Some of the Climate Benefits of Natural Gas". Scientific American. Retrieved 31 May 2023.</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">Plumer, Brad (26 June 2019). "As Coal Fades in the U.S., Natural Gas Becomes the Climate Battleground". The New York Times. Archived from the original on 23 September 2019. Retrieved 4 October 2019.</ref><ref>Gürsan, C.; de Gooyert, V. (2021). "The systemic impact of a transition fuel: Does natural gas help or hinder the energy transition?". Renewable and Sustainable Energy Reviews. 138: 110552. doi:10.1016/j.rser.2020.110552. hdl:2066/228782. ISSN 1364-0321. S2CID 228885573.</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>Budinis, Sarah (1 November 2018). "An assessment of CCS costs, barriers and potential". Energy Strategy Reviews. 22: 61–81. doi:10.1016/j.esr.2018.08.003. ISSN 2211-467X.</ref><ref>"Zero-emission carbon capture and storage in power plants using higher capture rates". IEA. 7 January 2021. Archived from the original on 30 March 2021. Retrieved 14 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>Ritchie, Hannah (10 February 2020). "What are the safest and cleanest sources of energy?". Our World in Data. Archived from the original on 29 November 2020. Retrieved 14 March 2021.</ref><ref>Evans, Simon (8 December 2017). "Solar, wind and nuclear have 'amazingly low' carbon footprints, study finds". Carbon Brief. Archived from the original on 16 March 2021. Retrieved 15 March 2021.</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.<ref name="FOOTNOTEIPCC20185.4.1.2">IPCC 2018, 5.4.1.2.</ref> The CCS process is expensive, with costs depending considerably on the location's proximity to suitable geology for carbon dioxide storage.<ref name=":11">Evans, Simon (27 August 2020). "Wind and solar are 30–50% cheaper than thought, admits UK government". Carbon Brief. Archived from the original on 23 September 2020. Retrieved 30 September 2020.</ref><ref>Malischek, Raimund. "CCUS in Power". IEA. Retrieved 30 September 2020.</ref> Deployment of this technology is still very limited, with only 21 large-scale CCS plants in operation worldwide as of 2020.<ref>Deign, Jason (7 December 2020). "Carbon Capture: Silver Bullet or Mirage?". Greentech Media. Archived from the original on 19 January 2021. Retrieved 14 February 2021.</ref>

Nuclear power

Main articles: Nuclear power debate and Nuclear renaissance

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>Roser, Max (10 December 2020). "The world's energy problem". Our World in Data. Archived from the original on 21 July 2021. Retrieved 21 July 2021.</ref>

Nuclear power has been used since the 1950s as a low-carbon source of baseload electricity.<ref>Rhodes, Richard (19 July 2018). "Why Nuclear Power Must Be Part of the Energy Solution". Yale Environment 360. Yale School of the Environment. Archived from the original on 9 August 2021. Retrieved 24 July 2021.</ref> Nuclear power plants in over 30 countries generate about 10% of global electricity.<ref>"Nuclear Power in the World Today". World Nuclear Association. June 2021. Archived from the original on 16 July 2021. Retrieved 19 July 2021.</ref> As of 2019, nuclear generated over a quarter of all low-carbon energy, making it the second largest source after hydropower.<ref name=":8">Ritchie, Hannah; Roser, Max (2020). "Energy mix". Our World in Data. Archived from the original on 2 July 2021. Retrieved 9 July 2021.</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 land per unit of energy produced, compared to the major renewables. Additionally, Nuclear power does not create local air pollution.<ref>Bailey, Ronald (10 May 2023). "New study: Nuclear power is humanity's greenest energy option". Reason.com. Retrieved 22 May 2023.</ref><ref>Ritchie, Hannah; Roser, Max (2020). "Nuclear Energy". Our World in Data. Archived from the original on 20 July 2021. Retrieved 19 July 2021.</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.<ref name="FOOTNOTEMacKay2008[httpswithouthotaircomc24page_162shtml 162]">MacKay 2008, p. 162.</ref><ref>Template:Citec</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>Muellner, Nikolaus; Arnold, Nikolaus; Gufler, Klaus; Kromp, Wolfgang; Renneberg, Wolfgang; Liebert, Wolfgang (2021). "Nuclear energy - The solution to climate change?". Energy Policy. 155. 112363. doi:10.1016/j.enpol.2021.112363. S2CID 236254316.</ref> Climate change mitigation pathways consistent with ambitious goals typically see an increase in power supply from nuclear.<ref name="FOOTNOTEIPCC20182.4.2.1">IPCC 2018, 2.4.2.1.</ref>

There is controversy over whether nuclear power is sustainable, in part due to concerns around nuclear waste, nuclear weapon proliferation, and accidents.<ref name=":14" /> Radioactive nuclear waste must be managed for thousands of years<ref name=":14">Template:Citec</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 accidental and pollution-related deaths than fossil fuels, and the historic fatality rate of nuclear is comparable to renewable sources.<ref name=cleanest/> 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 costs remain high and timescales long.<ref>Timmer, John (21 November 2020). "Why are nuclear plants so expensive? Safety's only part of the story". Ars Technica. Archived from the original on 28 April 2021. Retrieved 17 March 2021.</ref> Various new forms of nuclear energy are in development, hoping to address the drawbacks of conventional plants. Fast breeder reactors are capable of recycling nuclear waste and therefore can significantly reduce the amount of waste that requires geological disposal, but have not yet been deployed on a large-scale commercial basis.<ref>Technical assessment of nuclear energy with respect to the 'do no significant harm' criteria of Regulation (EU) 2020/852 ('Taxonomy Regulation') (PDF) (Report). European Commission Joint Research Centre. 2021. p. 53. Archived (PDF) from the original on 26 April 2021.</ref> 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>Template:Citec</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>Template:Citec</ref>

Several countries are attempting to develop nuclear fusion reactors, which would generate small amounts of waste and no risk of explosions.<ref>McGrath, Matt (6 November 2019). "Nuclear fusion is 'a question of when, not if'". BBC. Archived from the original on 25 January 2021. Retrieved 13 February 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>Amos, Jonathan (9 February 2022). "Major breakthrough on nuclear fusion energy". BBC. Archived from the original on 1 March 2022. Retrieved 10 February 2022.</ref>

Energy system transformation

Main article: Energy transition

Bloomberg NEF reported that in 2022, global energy transition investment equaled fossil fuels investment for the first time.<ref name=BloombergNEF_20230210>"Energy Transition Investment Now On Par with Fossil Fuel". Bloomberg NEF (New Energy Finance). 10 February 2023. Archived from the original on 27 March 2023.</ref>

The emissions reductions necessary to keep global warming below 2 °C will require a system-wide transformation of the way energy is produced, distributed, stored, and consumed.<ref name="FOOTNOTEUnited Nations Environment Programme201946">United Nations Environment Programme 2019, p. 46.</ref> 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 facilities and repair shops.<ref name="FOOTNOTEJaccard2020202–203[httpswwwcambridgeorgcorebookscitizens-guide-to-climate-successrenewables-have-wonF64DF99C3ED79CEA29C6EE2A59E71AB3core-reader Chapter 11 – "Renewables Have Won"]">Jaccard 2020, pp. 202–203, Chapter 11 – "Renewables Have Won".</ref>

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<ref name="FOOTNOTEIPCC20147.11.3">IPCC 2014, 7.11.3.</ref>

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.<ref name="FOOTNOTEIEA2021106–110">IEA 2021, pp. 106–110.</ref> 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.<ref name="FOOTNOTEJaccard2020203[httpswwwcambridgeorgcorebookscitizens-guide-to-climate-successrenewables-have-wonF64DF99C3ED79CEA29C6EE2A59E71AB3core-reader Chapter 11 – "Renewables Have Won"]">Jaccard 2020, p. 203, Chapter 11 – "Renewables Have Won".</ref> 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.<ref name="FOOTNOTEIEA202115">IEA 2021, p. 15.</ref> Developing new technologies requires research and development, demonstration, and cost reductions via deployment.<ref name="FOOTNOTEIEA202115">IEA 2021, p. 15.</ref> The transition to a zero-carbon energy system will bring strong co-benefits for human health: The World Health Organization estimates that efforts to limit global warming to 1.5 °C could save millions of lives each year from reductions to air pollution alone.<ref name="FOOTNOTEWorld Health Organization2018Executive Summary">World Health Organization 2018, Executive Summary.</ref><ref name="Vandyck_et_al_2018">Vandyck, T.; Keramidas, K.; Kitous, A.; Spadaro, J.V.; et al. (2018). "Air quality co-benefits for human health and agriculture counterbalance costs to meet Paris Agreement pledges". Nature Communications. 9 (1): 4939. Bibcode:2018NatCo...9.4939V. doi:10.1038/s41467-018-06885-9. PMC 6250710. PMID 30467311.</ref> With good planning and management, pathways exist to provide universal access to electricity and clean cooking by 2030 in ways that are consistent with climate goals.<ref name="FOOTNOTEUnited Nations Environment Programme201946–55">United Nations Environment Programme 2019, pp. 46–55.</ref><ref>IPCC 2018, p. 97</ref> Historically, several countries have made rapid economic gains through coal usage.<ref name="FOOTNOTEUnited Nations Environment Programme201946–55">United Nations Environment Programme 2019, pp. 46–55.</ref> However, there remains a window of opportunity for many poor countries and regions to "leapfrog" fossil fuel dependency by developing their energy systems based on renewables, given adequate international investment and knowledge transfer.<ref name="FOOTNOTEUnited Nations Environment Programme201946–55">United Nations Environment Programme 2019, pp. 46–55.</ref>

Integrating variable energy sources

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>Hopwood, David (2007). "Blueprint for sustainability?: What lessons can we learn from Freiburg's inclusive approach to sustainable development?". Refocus. 8 (3): 54–57. doi:10.1016/S1471-0846(07)70068-9. ISSN 1471-0846. Archived from the original on 2 November 2021. Retrieved 17 October 2021.</ref>

To deliver reliable electricity from variable renewable energy sources such as wind and solar, electrical power systems require flexibility.<ref name="FOOTNOTEUnited Nations Environment Programme201947">United Nations Environment Programme 2019, p. 47.</ref> Most electrical grids were constructed for non-intermittent energy sources such as coal-fired power plants.<ref>"Introduction to System Integration of Renewables". IEA. Archived from the original on 15 May 2020. Retrieved 30 May 2020.</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">Blanco, Herib; Faaij, André (2018). "A review at the role of storage in energy systems with a focus on Power to Gas and long-term storage" (PDF). Renewable and Sustainable Energy Reviews. 81: 1049–1086. doi:10.1016/j.rser.2017.07.062. ISSN 1364-0321.</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 long-distance transmission lines allows for further cancelling out of variability.<ref name="FOOTNOTEREN212020177">REN21 2020, p. 177.</ref> 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>Bloess, Andreas; Schill, Wolf-Peter; Zerrahn, Alexander (2018). "Power-to-heat for renewable energy integration: A review of technologies, modeling approaches, and flexibility potentials". Applied Energy. 212: 1611–1626. Bibcode:2018ApEn..212.1611B. doi:10.1016/j.apenergy.2017.12.073. hdl:10419/200120. S2CID 116132198.</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 curtailed if excess electricity cannot be used or stored. The final demand-supply mismatch may be covered by using dispatchable energy sources such as hydropower, bioenergy, or natural gas.<ref name="FOOTNOTEIEA2020109">IEA 2020, p. 109.</ref>

Energy storage

Main articles: Energy storage and Grid energy storage

Battery storage facility

Energy storage helps overcome barriers to intermittent renewable energy and is an important aspect of a sustainable energy system.<ref name=":16">Koohi-Fayegh, S.; Rosen, M.A. (2020). "A review of energy storage types, applications and recent developments". Journal of Energy Storage. 27: 101047. doi:10.1016/j.est.2019.101047. ISSN 2352-152X. S2CID 210616155. Archived from the original on 17 July 2021. Retrieved 28 November 2020.</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" /> Batteries, especially lithium-ion batteries, are also deployed widely.<ref>Katz, Cheryl (17 December 2020). "The batteries that could make fossil fuels obsolete". BBC. Archived from the original on 11 January 2021. Retrieved 10 January 2021.</ref> Batteries typically store electricity for short periods; research is ongoing into technology with sufficient capacity to last through seasons.<ref>Herib, Blanco; André, Faaij (2018). "A review at the role of storage in energy systems with a focus on Power to Gas and long-term storage" (PDF). Renewable and Sustainable Energy Reviews. 81: 1049–1086. doi:10.1016/j.rser.2017.07.062. ISSN 1364-0321.</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">"Climate change and batteries: the search for future power storage solutions" (PDF). Climate change: science and solutions. The Royal Society. 19 May 2021. Archived from the original on 16 October 2021. Retrieved 15 October 2021.</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>Hunt, Julian D.; Byers, Edward; Wada, Yoshihide; Parkinson, Simon; et al. (2020). "Global resource potential of seasonal pumped hydropower storage for energy and water storage". Nature Communications. 11 (1): 947. Bibcode:2020NatCo..11..947H. doi:10.1038/s41467-020-14555-y. ISSN 2041-1723. PMC 7031375. PMID 32075965.</ref><ref>Balaraman, Kavya (12 October 2020). "To batteries and beyond: With seasonal storage potential, hydrogen offers 'a different ballgame entirely'". Utility Dive. Archived from the original on 18 January 2021. Retrieved 10 January 2021.</ref>

Electrification

Main article: Electrification

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>Cole, Laura (15 November 2020). "How to cut carbon out of your heating". BBC. Archived from the original on 27 August 2021. Retrieved 31 August 2021.</ref>

Compared to the rest of the energy system, emissions can be reduced much faster in the electricity sector.<ref name="FOOTNOTEIPCC20147.11.3">IPCC 2014, 7.11.3.</ref> 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>Ritchie, Hannah; Roser, Max (2020). "Electricity Mix". Our World in Data. Archived from the original on 13 October 2021. Retrieved 16 October 2021.</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.<ref name="FOOTNOTEIPCC20147.11.3">IPCC 2014, 7.11.3.</ref>

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.<ref name="FOOTNOTEIPCC20147.11.3">IPCC 2014, 7.11.3.</ref> Ambitious climate policy would see a doubling of energy share consumed as electricity by 2050, from 20% in 2020.<ref name="FOOTNOTEIPCC20182.4.2.2">IPCC 2018, 2.4.2.2.</ref>

One of the challenges in providing universal access to electricity is distributing power to rural areas. Off-grid and 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.<ref name="FOOTNOTEIEA2021167–169">IEA 2021, pp. 167–169.</ref> Wider access to reliable electricity would lead to less use of kerosene lighting and diesel generators, which are currently common in the developing world.<ref name="FOOTNOTEUnited Nations Development Programme201630">United Nations Development Programme 2016, p. 30.</ref>

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">Herrington, Richard (2021). "Mining our green future". Nature Reviews Materials. 6 (6): 456–458. Bibcode:2021NatRM...6..456H. doi:10.1038/s41578-021-00325-9. ISSN 2058-8437.</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">Template:Citec</ref> Most of the world's cobalt, for instance, is 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>Babbitt, Callie W. (2020). "Sustainability perspectives on lithium-ion batteries". Clean Technologies and Environmental Policy. 22 (6): 1213–1214. Bibcode:2020CTEP...22.1213B. doi:10.1007/s10098-020-01890-3. ISSN 1618-9558. S2CID 220351269.</ref>

Hydrogen

Main article: Hydrogen economy

Hydrogen gas is widely discussed in the context of energy, as an energy carrier with potential to reduce greenhouse gas emissions.<ref name="FOOTNOTEIPCC AR6 WG3202291–92">IPCC AR6 WG3 2022, pp. 91–92.</ref><ref>Evans, Simon; Gabbatiss, Josh (30 November 2020). "In-depth Q&A: Does the world need hydrogen to solve climate change?". Carbon Brief. Archived from the original on 1 December 2020. Retrieved 1 December 2020.</ref> This requires hydrogen to be produced cleanly, in quantities to supply in sectors and applications where cheaper and more energy efficient mitigation alternatives are limited. These applications include heavy industry and long-distance transport.<ref name="FOOTNOTEIPCC AR6 WG3202291–92">IPCC AR6 WG3 2022, pp. 91–92.</ref>

Hydrogen can be deployed as an energy source in fuel cells to produce electricity, or via combustion to generate heat.<ref name=":0422">Lewis, Alastair C. (10 June 2021). "Optimising air quality co-benefits in a hydrogen economy: a case for hydrogen-specific standards for NO x emissions". Environmental Science: Atmospheres. 1 (5): 201–207. doi:10.1039/D1EA00037C. This article incorporates text from this source, which is available under the CC BY 3.0 license.</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 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>Reed, Stanley; Ewing, Jack (13 July 2021). "Hydrogen Is One Answer to Climate Change. Getting It Is the Hard Part". The New York Times. ISSN 0362-4331. Archived from the original on 14 July 2021. Retrieved 14 July 2021.</ref><ref>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">Bonheure, Mike; Vandewalle, Laurien A.; Marin, Guy B.; Van Geem, Kevin M. (March 2021). "Dream or Reality? Electrification of the Chemical Process Industries". CEP Magazine. American Institute of Chemical Engineers. Archived from the original on 17 July 2021. Retrieved 6 July 2021.</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, in part because of emissions (including vented and fugitive methane) created in the production of the natural gas itself.<ref name=":25">Griffiths, Steve; Sovacool, Benjamin K.; Kim, Jinsoo; Bazilian, Morgan; et al. (2021). "Industrial decarbonization via hydrogen: A critical and systematic review of developments, socio-technical systems and policy options" (PDF). Energy Research & Social Science. 80: 39. doi:10.1016/j.erss.2021.102208. ISSN 2214-6296. Retrieved 11 September 2021.</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">Evans, Simon; Gabbatiss, Josh (30 November 2020). "In-depth Q&A: Does the world need hydrogen to solve climate change?". Carbon Brief. Archived from the original on 1 December 2020. Retrieved 1 December 2020.</ref> Hydrogen can be produced when there is a surplus of variable renewable electricity, then stored and used to generate heat or to re-generate electricity.<ref>Palys, Matthew J.; Daoutidis, Prodromos (2020). "Using hydrogen and ammonia for renewable energy storage: A geographically comprehensive techno-economic study". Computers & Chemical Engineering. 136: 106785. doi:10.1016/j.compchemeng.2020.106785. ISSN 0098-1354. OSTI 1616471.</ref> It can be further transformed into liquid fuels such as green ammonia and green methanol.<ref name="FOOTNOTEIRENA202112, 22">IRENA 2021, pp. 12, 22.</ref> Innovation in hydrogen electrolysers could make large-scale production of hydrogen from electricity more cost-competitive.<ref name="FOOTNOTEIEA202115, 75–76">IEA 2021, pp. 15, 75–76.</ref>

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 furnaces for steelmaking.<ref>Kjellberg-Motton, Brendan (7 February 2022). "Steel decarbonisation gathers speed | Argus Media". www.argusmedia.com. Retrieved 7 September 2023.</ref> For steelmaking, hydrogen can function as a clean energy carrier and simultaneously as a low-carbon catalyst replacing coal-derived coke.<ref>Blank, Thomas; Molly, Patrick (January 2020). "Hydrogen's Decarbonization Impact for Industry" (PDF). Rocky Mountain Institute. pp. 2, 7, 8. Archived (PDF) from the original on 22 September 2020.</ref> Hydrogen used to decarbonise transportation is likely to find its largest applications in shipping, aviation and to a lesser extent heavy goods vehicles.<ref name="FOOTNOTEIPCC AR6 WG3202291–92">IPCC AR6 WG3 2022, pp. 91–92.</ref> For light duty vehicles including passenger cars, hydrogen is far behind other alternative fuel vehicles, especially compared with the rate of adoption of battery electric vehicles, and may not play a significant role in future.<ref>Plötz, Patrick (31 January 2022). "Hydrogen technology is unlikely to play a major role in sustainable road transport". Nature Electronics. 5 (1): 8–10. doi:10.1038/s41928-021-00706-6. ISSN 2520-1131. S2CID 246465284.</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

Utility cycling infrastructure, such as this bike lane in Vancouver, encourages sustainable transport.<ref>Fraser, Simon D.S.; Lock, Karen (December 2011). "Cycling for transport and public health: a systematic review of the effect of the environment on cycling". European Journal of Public Health. 21 (6): 738–743. doi:10.1093/eurpub/ckq145. PMID 20929903.</ref>

Main article: Sustainable transport

Transport accounts for 14% of global greenhouse gas emissions,<ref>"Global Greenhouse Gas Emissions Data". United States Environmental Protection Agency. 12 January 2016. Archived from the original on 5 December 2019. Retrieved 15 October 2021.</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>Bigazzi, Alexander (2019). "Comparison of marginal and average emission factors for passenger transportation modes". Applied Energy. 242: 1460–1466. Bibcode:2019ApEn..242.1460B. doi:10.1016/j.apenergy.2019.03.172. ISSN 0306-2619. S2CID 115682591. Archived from the original on 17 July 2021. Retrieved 8 February 2021.</ref><ref>Schäfer, Andreas W.; Yeh, Sonia (2020). "A holistic analysis of passenger travel energy and greenhouse gas intensities" (PDF). Nature Sustainability. 3 (6): 459–462. Bibcode:2020NatSu...3..459S. doi:10.1038/s41893-020-0514-9. ISSN 2398-9629. S2CID 216032098.</ref> Short-distance flights can be replaced by high-speed rail, which is more efficient, especially when electrified.<ref name="FOOTNOTEUnited Nations Environment Programme2020xxv">United Nations Environment Programme 2020, p. xxv.</ref><ref name="FOOTNOTEIEA2021137">IEA 2021, p. 137.</ref> Promoting non-motorised transport such as walking and cycling, particularly in cities, can make transport cleaner and healthier.<ref>Pucher, John; Buehler, Ralph (2017). "Cycling towards a more sustainable transport future". Transport Reviews. 37 (6): 689–694. doi:10.1080/01441647.2017.1340234. ISSN 0144-1647.</ref><ref>Smith, John (22 September 2016). "Sustainable transport". European Commission. Archived from the original on 22 October 2021. Retrieved 22 October 2021.</ref>

The energy efficiency of cars has increased over time,<ref>Knobloch, Florian; Hanssen, Steef V.; Lam, Aileen; Pollitt, Hector; et al. (2020). "Net emission reductions from electric cars and heat pumps in 59 world regions over time". Nature Sustainability. 3 (6): 437–447. Bibcode:2020NatSu...3..437K. doi:10.1038/s41893-020-0488-7. ISSN 2398-9629. PMC 7308170. PMID 32572385.</ref> but shifting to electric vehicles is an important further step towards decarbonising transport and reducing air pollution.<ref name=":17">Bogdanov, Dmitrii; Farfan, Javier; Sadovskaia, Kristina; Aghahosseini, Arman; et al. (2019). "Radical transformation pathway towards sustainable electricity via evolutionary steps". Nature Communications. 10 (1): 1077. Bibcode:2019NatCo..10.1077B. doi:10.1038/s41467-019-08855-1. 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>Martini, Giorgio; Grigoratos, Theodoros (2014). Non-exhaust traffic related emissions – Brake and tyre wear PM. EUR 26648. Publications Office of the European Union. p. 42. ISBN 978-92-79-38303-8. OCLC 1044281650. Archived from the original on 30 July 2021.</ref> Substantially reducing pollution from these non-tailpipe sources cannot be achieved by electrification; it requires measures such as making vehicles lighter and driving them less.<ref>"Executive Summary". Non-exhaust Particulate Emissions from Road Transport: An Ignored Environmental Policy Challenge. OECD Publishing. 2020. pp. 8–9. doi:10.1787/4a4dc6ca-en. ISBN 978-92-64-45244-2. S2CID 136987659. Archived from the original on 30 July 2021.</ref> Light-duty cars in particular are a prime candidate for decarbonization using battery technology. 25% of the world's CO₂ emissions still originate from the transportation sector.<ref>"CO₂ performance of new passenger cars in Europe". www.eea.europa.eu. Retrieved 19 October 2022.</ref>

Long-distance freight transport and aviation are difficult sectors to electrify with current technologies, mostly because of the weight of batteries needed for long-distance travel, battery recharging times, and limited battery lifespans.<ref name="FOOTNOTEIEA2021133–137">IEA 2021, pp. 133–137.</ref><ref name=":2" /> Where available, freight transport by ship and rail is generally more sustainable than by air and by road.<ref>"Rail and waterborne – best for low-carbon motorised transport". European Environment Agency. Archived from the original on 9 October 2021. Retrieved 15 October 2021.</ref> Hydrogen vehicles may be an option for larger vehicles such as lorries.<ref>Miller, Joe (9 September 2020). "Hydrogen takes a back seat to electric for passenger vehicles". Financial Times. Archived from the original on 20 September 2020. Retrieved 9 September 2020.</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.<ref name="FOOTNOTEIEA2021136, 139">IEA 2021, pp. 136, 139.</ref> 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">Biomass in a low-carbon economy (Report). UK Committee on Climate Change. November 2018. p. 18. Archived from the original on 28 December 2019. Retrieved 28 December 2019.</ref>

Buildings and cooking

Further information: Renewable heat, Green building, and Energy poverty and cooking

Passive cooling features, such as these windcatcher towers in Iran, bring cool air into buildings without any use of energy.<ref>Abdolhamidi, Shervin (27 September 2018). "An ancient engineering feat that harnessed the wind". BBC. Archived from the original on 12 August 2021. Retrieved 12 August 2021.</ref>

For cooking, electric induction stoves are one of the most energy-efficient and safest options.<ref name="FOOTNOTESmithPillarisetti2017145–146">Smith & Pillarisetti 2017, pp. 145–146.</ref><ref>"Cooking appliances". Natural Resources Canada. 16 January 2013. Archived from the original on 30 July 2021. Retrieved 30 July 2021.</ref>

Over one-third of energy use is in buildings and their construction.<ref>"Buildings". IEA. Archived from the original on 14 October 2021. Retrieved 15 October 2021.</ref> To heat buildings, alternatives to burning fossil fuels and biomass include electrification through heat pumps or electric heaters, geothermal energy, central solar heating, reuse of waste heat, and seasonal thermal energy storage.<ref>Mortensen, Anders Winther; Mathiesen, Brian Vad; Hansen, Anders Bavnhøj; Pedersen, Sigurd Lauge; et al. (2020). "The role of electrification and hydrogen in breaking the biomass bottleneck of the renewable energy system – A study on the Danish energy system" (PDF). Applied Energy. 275: 115331. Bibcode:2020ApEn..27515331M. doi:10.1016/j.apenergy.2020.115331. ISSN 0306-2619.</ref><ref name=":12">Knobloch, Florian; Pollitt, Hector; Chewpreecha, Unnada; Daioglou, Vassilis; et al. (2019). "Simulating the deep decarbonisation of residential heating for limiting global warming to 1.5 °C" (PDF). Energy Efficiency. 12 (2): 521–550. doi:10.1007/s12053-018-9710-0. ISSN 1570-6478. S2CID 52830709.</ref><ref>Alva, Guruprasad; Lin, Yaxue; Fang, Guiyin (2018). "An overview of thermal energy storage systems". Energy. 144: 341–378. doi:10.1016/j.energy.2017.12.037. ISSN 0360-5442. Archived from the original on 17 July 2021. Retrieved 28 November 2020.</ref> Heat pumps provide both heat and air conditioning through a single appliance.<ref>Plumer, Brad (30 June 2021). "Are 'Heat Pumps' the Answer to Heat Waves? Some Cities Think So". The New York Times. ISSN 0362-4331. Archived from the original on 10 September 2021. Retrieved 11 September 2021.</ref> The IEA estimates heat pumps could provide over 90% of space and water heating requirements globally.<ref>Abergel, Thibaut (June 2020). "Heat Pumps". IEA. Archived from the original on 3 March 2021. Retrieved 12 April 2021.</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 pipes. Traditionally, most district heating systems have used fossil fuels, but modern and cold district heating systems are designed to use high shares of renewable energy.<ref>Buffa, Simone; Cozzini, Marco; D'Antoni, Matteo; Baratieri, Marco; et al. (2019). "5th generation district heating and cooling systems: A review of existing cases in Europe". Renewable and Sustainable Energy Reviews. 104: 504–522. doi:10.1016/j.rser.2018.12.059.</ref><ref>Lund, Henrik; Werner, Sven; Wiltshire, Robin; Svendsen, Svend; et al. (2014). "4th Generation District Heating (4GDH)". Energy. 68: 1–11. doi:10.1016/j.energy.2014.02.089. Archived from the original on 7 March 2021. Retrieved 13 June 2021.</ref>

Cooling of buildings can be made more efficient through passive building design, planning that minimises the urban heat island effect, and district cooling systems that cool multiple buildings with piped cold water.<ref>"How cities are using nature to keep heatwaves at bay". United Nations Environment Programme. 22 July 2020. Archived from the original on 11 September 2021. Retrieved 11 September 2021.</ref><ref name=":26">"Four Things You Should Know About Sustainable Cooling". World Bank. 23 May 2019. Archived from the original on 11 September 2021. Retrieved 11 September 2021.</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 refrigerants that are greenhouse gases, as some countries have not ratified the Kigali Amendment to only use climate-friendly refrigerants.<ref>Mastrucci, Alessio; Byers, Edward; Pachauri, Shonali; Rao, Narasimha D. (2019). "Improving the SDG energy poverty targets: Residential cooling needs in the Global South" (PDF). Energy and Buildings. 186: 405–415. doi:10.1016/j.enbuild.2019.01.015. ISSN 0378-7788.</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>World Health Organization; International Energy Agency; Global Alliance for Clean Cookstoves; United Nations Development Programme; Energising Development; and World Bank (2018). Accelerating SDG 7 Achievement Policy Brief 02: Achieving Universal Access to Clean and Modern Cooking Fuels, Technologies and Services (PDF) (Report). United Nations. p. 3. Archived (PDF) from the original on 18 March 2021.</ref> The universal adoption of clean cooking facilities, which are already ubiquitous in rich countries,<ref name="FOOTNOTESmithPillarisetti2017145–146">Smith & Pillarisetti 2017, pp. 145–146.</ref> would dramatically improve health and have minimal negative effects on climate.<ref name="FOOTNOTEWorld Health Organization201675">World Health Organization 2016, p. 75.</ref><ref name="FOOTNOTEIPCC201429">IPCC 2014, p. 29.</ref> 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.<ref name="FOOTNOTESmithPillarisetti2017145–146">Smith & Pillarisetti 2017, pp. 145–146.</ref> Improved cookstoves that burn biomass more efficiently than traditional stoves are an interim solution where transitioning to clean cooking systems is difficult.<ref name="FOOTNOTEWorld Health Organization201612">World Health Organization 2016, p. 12.</ref>

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 200 °C (390 °F).<ref name="FOOTNOTEREN21202040">REN21 2020, p. 40.</ref>

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.<ref name="FOOTNOTEIEA2020135">IEA 2020, p. 135.</ref> Steelmaking, for instance, is difficult to electrify because it traditionally uses coke, which is derived from coal, both to create very high-temperature heat and as an ingredient in the steel itself.<ref name="FOOTNOTEUnited Nations Environment Programme201950">United Nations Environment Programme 2019, p. 50.</ref> The production of plastic, cement, and fertilisers also requires significant amounts of energy, with limited possibilities available to decarbonise.<ref>Åhman, Max; Nilsson, Lars J.; Johansson, Bengt (2017). "Global climate policy and deep decarbonization of energy-intensive industries". Climate Policy. 17 (5): 634–649. Bibcode:2017CliPo..17..634A. doi:10.1080/14693062.2016.1167009. ISSN 1469-3062.</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.<ref name="FOOTNOTEUnited Nations Environment Programme2019xxiii">United Nations Environment Programme 2019, p. xxiii.</ref>

Government policies

Further information: Politics of climate change and Energy policy

"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."

International Energy Agency (2021)<ref name="FOOTNOTEIEA2021186">IEA 2021, p. 186.</ref>

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.<ref name="FOOTNOTEUnited Nations Environment Programme201939–45">United Nations Environment Programme 2019, pp. 39–45.</ref>

Environmental regulations have been used since the 1970s to promote more sustainable use of energy.<ref name="FOOTNOTEJaccard2020109[httpswwwcambridgeorgcorebookscitizens-guide-to-climate-successwe-must-price-carbon-emissions66AEBB8BE9A7F7760DC1BCE3A9C50748 Chapter 6 – We Must Price Carbon Emissions"]">Jaccard 2020, p. 109, Chapter 6 – We Must Price Carbon Emissions".</ref> Some governments have committed to dates for 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.<ref name="FOOTNOTEUnited Nations Environment Programme201928–36">United Nations Environment Programme 2019, pp. 28–36.</ref> Renewable portfolio standards in several countries require utilities to increase the percentage of electricity they generate from renewable sources.<ref>Ciucci, M. (February 2020). "Renewable Energy". European Parliament. Archived from the original on 4 June 2020. Retrieved 3 June 2020.</ref><ref>"State Renewable Portfolio Standards and Goals". National Conference of State Legislators. 17 April 2020. Archived from the original on 3 June 2020. Retrieved 3 June 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.<ref name="FOOTNOTEIEA202114–25">IEA 2021, pp. 14–25.</ref> In transport, appropriate infrastructure and incentives can make travel more efficient and less car-dependent.<ref name="FOOTNOTEUnited Nations Environment Programme201939–45">United Nations Environment Programme 2019, pp. 39–45.</ref> Urban planning that discourages sprawl can reduce energy use in local transport and buildings while enhancing quality of life.<ref name="FOOTNOTEUnited Nations Environment Programme201939–45">United Nations Environment Programme 2019, pp. 39–45.</ref> 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.<ref name="FOOTNOTEIEA2021184–187">IEA 2021, pp. 184–187.</ref> 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.<ref name="FOOTNOTEIEA202116">IEA 2021, p. 16.</ref>

Several countries and the European Union have committed to dates for all new cars to be zero-emissions vehicles.<ref name="FOOTNOTEUnited Nations Environment Programme201928–36">United Nations Environment Programme 2019, pp. 28–36.</ref>

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.<ref name="FOOTNOTEJaccard2020106–109[httpswwwcambridgeorgcorebookscitizens-guide-to-climate-successwe-must-price-carbon-emissions66AEBB8BE9A7F7760DC1BCE3A9C50748 Chapter 6 – "We Must Price Carbon Emissions"]">Jaccard 2020, pp. 106–109, Chapter 6 – "We Must Price Carbon Emissions".</ref> Carbon pricing has encountered strong political pushback in some jurisdictions, whereas energy-specific policies tend to be politically safer.<ref name="Plumer">Plumer, Brad (8 October 2018). "New U.N. Climate Report Says Put a High Price on Carbon". The New York Times. ISSN 0362-4331. Archived from the original on 27 September 2019. Retrieved 4 October 2019.</ref><ref>Green, Jessica F. (2021). "Does carbon pricing reduce emissions? A review of ex-post analyses". Environmental Research Letters. 16 (4): 043004. Bibcode:2021ERL....16d3004G. doi:10.1088/1748-9326/abdae9. ISSN 1748-9326. S2CID 234254992.</ref> Most studies indicate that to limit global warming to 1.5 °C, carbon pricing would need to be complemented by stringent energy-specific policies.<ref name="FOOTNOTEIPCC20182.5.2.1">IPCC 2018, 2.5.2.1.</ref> As of 2019, the price of carbon in most regions is too low to achieve the goals of the Paris Agreement.<ref> State and Trends of Carbon Pricing 2019 (PDF) (Report). World Bank. June 2019. pp. 8–11. doi:10.1596/978-1-4648-1435-8. hdl:10986/29687. ISBN 978-1-4648-1435-8. Archived (PDF) from the original on 6 May 2020. </ref> Carbon taxes provide a source of revenue that can be used to lower other taxes<ref>"Revenue-Neutral Carbon Tax | Canada". United Nations Framework Convention on Climate Change. Archived from the original on 28 October 2019. Retrieved 28 October 2019.</ref> or help lower-income households afford higher energy costs.<ref>Carr, Mathew (10 October 2018). "How High Does Carbon Need to Be? Somewhere From $20–$27,000". Bloomberg. Archived from the original on 5 August 2019. Retrieved 4 October 2019.</ref> Some governments, such as the EU and the UK, are exploring the use of carbon border adjustments.<ref>"EAC launches new inquiry weighing up carbon border tax measures". UK Parliament. 24 September 2021. Archived from the original on 24 September 2021. Retrieved 14 October 2021.</ref> These place tariffs on imports from countries with less stringent climate policies, to ensure that industries subject to internal carbon prices remain competitive.<ref>Plumer, Brad (14 July 2021). "Europe Is Proposing a Border Carbon Tax. What Is It and How Will It Work?". The New York Times. ISSN 0362-4331. Archived from the original on 10 September 2021. Retrieved 10 September 2021.</ref><ref>Bharti, Bianca (12 August 2021). "Taxing imports of heavy carbon emitters is gaining momentum – and it could hurt Canadian industry: Report". Financial Post. Archived from the original on 3 October 2021. Retrieved 3 October 2021.</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.<ref name="FOOTNOTEUnited Nations Environment Programme2020vii">United Nations Environment Programme 2020, p. vii.</ref><ref name="FOOTNOTEIEA202113">IEA 2021, p. 13.</ref> 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.<ref name="FOOTNOTEIEA202114–18">IEA 2021, pp. 14–18.</ref>

Countries may support renewables to create jobs.<ref name="FOOTNOTEIRENAIEAREN21201819">IRENA, IEA & REN21 2018, p. 19.</ref> The International Labour Organization estimates that efforts to limit global warming to 2 °C would result in net job creation in most sectors of the economy.<ref name=":21">"24 million jobs to open up in the green economy". International Labour Organization. 14 May 2018. Archived from the original on 2 June 2021. Retrieved 30 May 2021.</ref> It predicts that 24 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.<ref name="FOOTNOTEUnited Nations Environment Programme201946–55">United Nations Environment Programme 2019, pp. 46–55.</ref>

Finance

Further information: Climate finance

Electrified transport and renewable energy are key areas of investment for the renewable energy transition.<ref name=BloombergNEF_20230126>Catsaros, Oktavia (26 January 2023). "Global Low-Carbon Energy Technology Investment Surges Past $1 Trillion for the First Time". Bloomberg NEF (New Energy Finance). Figure 1. Archived from the original on 22 May 2023. Defying supply chain disruptions and macroeconomic headwinds, 2022 energy transition investment jumped 31% to draw level with fossil fuels</ref>

Raising enough money for innovation and investment is a prerequisite for the energy transition.<ref name=":22">Mazzucato, Mariana; Semieniuk, Gregor (2018). "Financing renewable energy: Who is financing what and why it matters" (PDF). Technological Forecasting and Social Change. 127: 8–22. doi:10.1016/j.techfore.2017.05.021. ISSN 0040-1625.</ref> The IPCC estimates that to limit global warming to 1.5 °C, US$2.4 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.<ref name="FOOTNOTEUnited Nations Development ProgrammeUnited Nations Framework Convention on Climate Change201924">United Nations Development Programme & United Nations Framework Convention on Climate Change 2019, p. 24.</ref> Average annual investment in low-carbon energy technologies and energy efficiency would need to be six times more by 2050 compared to 2015.<ref name="FOOTNOTEIPCC201896">IPCC 2018, p. 96.</ref> Underfunding is particularly acute in the least developed countries, which are not attractive to the private sector.<ref name="FOOTNOTEIEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization2021129, 132">IEA, IRENA, United Nations Statistics Division, World Bank, World Health Organization 2021, pp. 129, 132.</ref>

The United Nations Framework Convention on Climate Change estimates that climate financing totalled $681 billion in 2016.<ref name="FOOTNOTEUnited Nations Framework Convention on Climate Change201854">United Nations Framework Convention on Climate Change 2018, p. 54.</ref> Most of this is private-sector investment in renewable energy deployment, public-sector investment in sustainable transport, and private-sector investment in energy efficiency.<ref name="FOOTNOTEUnited Nations Framework Convention on Climate Change20189">United Nations Framework Convention on Climate Change 2018, p. 9.</ref> The Paris Agreement includes a pledge of an extra $100 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>Roberts, J. Timmons; Weikmans, Romain; Robinson, Stacy-ann; Ciplet, David; et al. (2021). "Rebooting a failed promise of climate finance" (PDF). Nature Climate Change. 11 (3): 180–182. Bibcode:2021NatCC..11..180R. doi:10.1038/s41558-021-00990-2. ISSN 1758-6798.</ref><ref>Radwanski, Adam (29 September 2021). "Opinion: As pivotal climate summit approaches, Canada at centre of efforts to repair broken trust among poorer countries". The Globe and Mail. Archived from the original on 30 September 2021. Retrieved 30 September 2021.</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">"Here are the clean energy innovations that will beat climate change". European Investment Bank. Retrieved 26 September 2022.</ref><ref>"Home". www.oecd-ilibrary.org. Retrieved 19 October 2022.</ref>

Fossil fuel funding and subsidies are a significant barrier to the energy transition.<ref>Bridle, Richard; Sharma, Shruti; Mostafa, Mostafa; Geddes, Anna (June 2019). "Fossil Fuel to Clean Energy Subsidy Swaps: How to pay for an energy revolution" (PDF). International Institute for Sustainable Development. p. iv. Archived (PDF) from the original on 17 November 2019.</ref><ref name=":22" /> Direct global fossil fuel subsidies were $319 billion in 2017. This rises to $5.2 trillion when indirect costs are priced in, like the effects of air pollution.<ref name="Watts_et_al_2019">Watts, N.; Amann, M.; Arnell, N.; Ayeb-Karlsson, S.; et al. (2019). "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" (PDF). The Lancet. 394 (10211): 1836–1878. doi:10.1016/S0140-6736(19)32596-6. PMID 31733928. S2CID 207976337. Retrieved 3 November 2021.</ref> Ending these could lead to a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths.<ref name="FOOTNOTEUnited Nations Development Programme202010">United Nations Development Programme 2020, p. 10.</ref> 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>Kuzemko, Caroline; Bradshaw, Michael; Bridge, Gavin; Goldthau, Andreas; et al. (2020). "Covid-19 and the politics of sustainable energy transitions". Energy Research & Social Science. 68: 101685. doi:10.1016/j.erss.2020.101685. ISSN 2214-6296. PMC 7330551. PMID 32839704.</ref><ref name="FOOTNOTEIRENA20215">IRENA 2021, p. 5.</ref>

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