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[[File:Change in Average Temperature With Fahrenheit.svg|thumb|upright=1.35|alt=The global map shows sea temperature rises of 0.5 to 1 degree Celsius; land temperature rises of 1 to 2 degrees Celsius; and Arctic temperature rises of up to 4 degrees Celsius.|Changes in [[surface air temperature]] over the past 50 years.<ref>{{Cite web |title=GISS Surface Temperature Analysis (v4) |url=https://data.giss.nasa.gov/gistemp/maps/index_v4.html |access-date=12 January 2024 |website=NASA}}</ref> The [[Arctic]] has warmed the most, and temperatures on land have generally increased more than [[sea surface temperature]]s.]]
[[File:Change in Average Temperature With Fahrenheit.svg|thumb|upright=1.35|alt=The global map shows sea temperature rises of 0.5 to 1 degree Celsius; land temperature rises of 1 to 2 degrees Celsius; and Arctic temperature rises of up to 4 degrees Celsius.|Changes in [[surface air temperature]] over the past 50 years.<ref>{{Cite web |title=GISS Surface Temperature Analysis (v4) |url=https://data.giss.nasa.gov/gistemp/maps/index_v4.html |access-date=12 January 2024 |website=NASA}}</ref> The [[Arctic]] has warmed the most, and temperatures on land have generally increased more than [[sea surface temperature]]s.]]
[[File:Global Temperature And Forces With Fahrenheit.svg|thumb|upright=1.35|Earth's average surface air temperature has increased almost 1.5{{nbsp}}°C (about{{nbsp}}2.5 °F) since the [[Industrial Revolution]]. Natural forces cause some variability, but the 20-year average shows the progressive influence of human activity.<ref>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|loc=SPM-7}}</ref>]]
[[File:Global Temperature And Forces With Fahrenheit.svg|thumb|upright=1.35|Earth's average surface air temperature has increased almost 1.5{{nbsp}}°C (about{{nbsp}}2.5&nbsp;°F) since the [[Industrial Revolution]]. Natural forces cause some variability, but the 20-year average shows the progressive influence of human activity.<ref>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|loc=SPM-7}}</ref>]]
<!--Please do not change the content in the lead section without first proposing the change on the talk page, and please limit overall length to under 500 words.-->
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Present-day '''climate change''' includes both '''global warming'''—the ongoing increase in [[Global surface temperature|global average temperature]]—and its wider effects on [[Climate system|Earth's climate]]. [[Climate variability and change|Climate change in a broader sense]] also includes previous long-term changes to Earth's climate. The current rise in global temperatures is [[Scientific consensus on climate change|driven by human activities]], especially [[fossil fuel]] burning since the [[Industrial Revolution]].<ref>{{harvnb|Forster|Smith|Walsh|Lamb|2024|p=2626}}: "The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced."</ref><ref name=Lynas_2021>{{cite journal |last1=Lynas |first1=Mark |last2=Houlton |first2=Benjamin Z. |last3=Perry |first3=Simon |title=Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature |journal=[[Environmental Research Letters]] |date=19 October 2021 |volume=16 |issue=11 |page=114005 |doi=10.1088/1748-9326/ac2966 |bibcode=2021ERL....16k4005L |s2cid=239032360 |doi-access=free |issn = 1748-9326}}</ref> Fossil fuel use, [[Deforestation and climate change|deforestation]], and some [[Greenhouse gas emissions from agriculture|agricultural]] and [[Environmental impact of concrete|industrial]] practices release [[greenhouse gas]]es.<ref name="Our World in Data-2020">{{harvnb|Our World in Data, 18 September|2020}}</ref> These gases [[greenhouse effect|absorb some of the heat]] that the Earth [[Thermal radiation|radiates]] after it warms from [[sunlight]], warming the lower atmosphere. [[Carbon dioxide]], the primary greenhouse gas driving global warming, [[Carbon dioxide in Earth's atmosphere|has grown by about 50%]] and is at levels unseen for millions of years.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=67}}: "Concentrations of {{CO2}}, methane ({{CH4}}), and nitrous oxide ({{N2O}}) have increased to levels unprecedented in at least 800,000 years, and there is high confidence that current {{CO2}} concentrations have not been experienced for at least 2 million years."</ref>
Present-day '''climate change''' includes both '''global warming'''—the ongoing increase in [[Global surface temperature|global average temperature]]—and its wider effects on [[Climate system|Earth's climate]]. [[Climate variability and change|Climate change in a broader sense]] also includes previous long-term changes to Earth's climate. The current rise in global temperatures is [[Scientific consensus on climate change|driven by human activities]], especially [[fossil fuel]] burning since the [[Industrial Revolution]].<ref>{{harvnb|Forster|Smith|Walsh|Lamb|2024|p=2626}}: "The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced."</ref><ref name=Lynas_2021>{{cite journal |last1=Lynas |first1=Mark |last2=Houlton |first2=Benjamin Z. |last3=Perry |first3=Simon |title=Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature |journal=[[Environmental Research Letters]] |date=19 October 2021 |volume=16 |issue=11 |page=114005 |doi=10.1088/1748-9326/ac2966 |bibcode=2021ERL....16k4005L |s2cid=239032360 |doi-access=free |issn = 1748-9326}}</ref> Fossil fuel use, [[Deforestation and climate change|deforestation]], and some [[Greenhouse gas emissions from agriculture|agricultural]] and [[Environmental impact of concrete|industrial]] practices release [[greenhouse gas]]es.<ref name="Our World in Data-2020">{{harvnb|Our World in Data, 18 September|2020}}</ref> These gases [[greenhouse effect|absorb some of the heat]] that the Earth [[Thermal radiation|radiates]] after it warms from [[sunlight]], warming the lower atmosphere. [[Carbon dioxide]], the primary greenhouse gas driving global warming, [[Carbon dioxide in Earth's atmosphere|has grown by about 50%]] and is at levels not seen for millions of years.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=67}}: "Concentrations of {{CO2}}, methane ({{CH4}}), and nitrous oxide ({{N2O}}) have increased to levels unprecedented in at least 800,000 years, and there is high confidence that current {{CO2}} concentrations have not been experienced for at least 2 million years."</ref>


Climate change has an increasingly large [[Effects of climate change|impact on the environment]]. [[Desertification|Deserts are expanding]], while [[heat wave]]s and [[wildfire]]s are becoming more common.<ref>
Climate change has an increasingly large [[Effects of climate change|impact on the environment]]. [[Desertification|Deserts are expanding]], while [[heat wave]]s and [[Wildfire#Climate change effects|wildfire]]s are becoming more common.<ref>
* {{harvnb|IPCC SRCCL|2019|p=7}}: "Since the pre-industrial period, the land surface air temperature has risen nearly twice as much as the global average temperature (high confidence). Climate change... contributed to desertification and land degradation in many regions (high confidence)."
* {{harvnb|IPCC SRCCL|2019|p=7}}: "Since the pre-industrial period, the land surface air temperature has risen nearly twice as much as the global average temperature (high confidence). Climate change... contributed to desertification and land degradation in many regions (high confidence)."
* {{harvnb|IPCC AR6 WG2 SPM|2022|p=9}}: "Observed increases in areas burned by wildfires have been attributed to human-induced climate change in some regions (medium to high confidence)"</ref> [[polar amplification|Amplified warming in the Arctic]] has contributed to thawing [[permafrost]], [[retreat of glaciers since 1850|retreat of glaciers]] and [[Arctic sea ice decline|sea ice decline]].<ref>{{harvnb|IPCC SROCC|2019|p=16}}: "Over the last decades, global warming has led to widespread shrinking of the cryosphere, with mass loss from ice sheets and glaciers (very high confidence), reductions in snow cover (high confidence) and Arctic sea ice extent and thickness (very high confidence), and increased permafrost temperature (very high confidence)."</ref> Higher temperatures are also causing [[Tropical cyclones and climate change|more intense storms]], droughts, and other [[Extreme weather|weather extremes]].<ref>{{Harvnb|IPCC AR6 WG1 Ch11|2021|p=1517}}</ref> Rapid environmental change in [[Montane ecosystems|mountains]], [[coral reef]]s, and [[Climate change in the Arctic|the Arctic]] is forcing many species to relocate or [[Extinction risk from climate change|become extinct]].<ref>{{cite web|author=EPA|date=19 January 2017|title=Climate Impacts on Ecosystems|url=https://19january2017snapshot.epa.gov/climate-impacts/climate-impacts-ecosystems_.html#Extinction|url-status=live|archive-url=https://web.archive.org/web/20180127185656/https://19january2017snapshot.epa.gov/climate-impacts/climate-impacts-ecosystems_.html#Extinction|archive-date=27 January 2018|access-date=5 February 2019|quote=Mountain and arctic ecosystems and species are particularly sensitive to climate change... As ocean temperatures warm and the acidity of the ocean increases, bleaching and coral die-offs are likely to become more frequent.}}</ref> Even if efforts to minimize future warming are successful, some effects will continue for centuries. These include [[Ocean temperature#Increasing temperature due to climate change|ocean heating]], [[ocean acidification]] and [[sea level rise]].<ref>{{harvnb|IPCC SR15 Ch1|2018|p=64}}: "Sustained net zero anthropogenic emissions of {{CO2}} and declining net anthropogenic non-{{CO2}} radiative forcing over a multi-decade period would halt anthropogenic global warming over that period, although it would not halt sea level rise or many other aspects of climate system adjustment."</ref>
* {{harvnb|IPCC AR6 WG2 SPM|2022|p=9}}: "Observed increases in areas burned by wildfires have been attributed to human-induced climate change in some regions (medium to high confidence)"</ref> [[polar amplification|Amplified warming in the Arctic]] has contributed to thawing [[permafrost]], [[retreat of glaciers since 1850|retreat of glaciers]] and [[Arctic sea ice decline|sea ice decline]].<ref>{{harvnb|IPCC SROCC|2019|p=16}}: "Over the last decades, global warming has led to widespread shrinking of the cryosphere, with mass loss from ice sheets and glaciers (very high confidence), reductions in snow cover (high confidence) and Arctic sea ice extent and thickness (very high confidence), and increased permafrost temperature (very high confidence)."</ref> Higher temperatures are also causing [[Tropical cyclones and climate change|more intense storms]], droughts, and other [[Extreme weather|weather extremes]].<ref>{{Harvnb|IPCC AR6 WG1 Ch11|2021|p=1517}}</ref> Rapid environmental change in [[Montane ecosystems|mountains]], [[coral reef]]s, and [[Climate change in the Arctic|the Arctic]] is forcing many species to relocate or [[Extinction risk from climate change|become extinct]].<ref>{{cite web|author=EPA|date=19 January 2017|title=Climate Impacts on Ecosystems|url=https://19january2017snapshot.epa.gov/climate-impacts/climate-impacts-ecosystems_.html#Extinction|url-status=live|archive-url=https://web.archive.org/web/20180127185656/https://19january2017snapshot.epa.gov/climate-impacts/climate-impacts-ecosystems_.html#Extinction|archive-date=27 January 2018|access-date=5 February 2019|quote=Mountain and arctic ecosystems and species are particularly sensitive to climate change... As ocean temperatures warm and the acidity of the ocean increases, bleaching and coral die-offs are likely to become more frequent.}}</ref> Even if efforts to minimize future warming are successful, some effects will continue for centuries. These include [[Ocean temperature#Increasing temperature due to climate change|ocean heating]], [[ocean acidification]] and [[sea level rise]].<ref>{{harvnb|IPCC SR15 Ch1|2018|p=64}}: "Sustained net zero anthropogenic emissions of {{CO2}} and declining net anthropogenic non-{{CO2}} radiative forcing over a multi-decade period would halt anthropogenic global warming over that period, although it would not halt sea level rise or many other aspects of climate system adjustment."</ref>
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Many climate change impacts have been felt in recent years, with 2023 the warmest on record at +{{convert|1.48|C-change}} since regular tracking began in 1850.<ref>{{cite web |title=2023 confirmed as world's hottest year on record |url=https://www.bbc.com/news/science-environment-67861954 |publisher=[[BBC]] |first1=Mark |last1=Poynting |first2=Erwan |last2=Rivault |access-date=13 January 2024 |date=10 January 2024}}</ref><ref>{{Cite web |date=21 April 2023 |title=Human, economic, environmental toll of climate change on the rise: WMO {{!}} UN News |url=https://news.un.org/en/story/2023/04/1135852 |access-date=11 April 2024 |website=news.un.org |language=en}}</ref> Additional warming will increase these impacts and can trigger [[Tipping points in the climate system|tipping points]], such as melting all of the [[Greenland ice sheet]].<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=71}}</ref> Under the 2015 [[Paris Agreement]], nations collectively agreed to keep warming "well under 2&nbsp;°C". However, with pledges made under the Agreement, global warming would still reach about {{convert|2.8|C-change}} by the end of the century.<ref name="UNEP2024">{{harvnb|United Nations Environment Programme|2024|p=XVIII}}: "The full implementation and continuation of the level of mitigation effort implied by unconditional or conditional NDC scenarios lower these projections to 2.8&nbsp;°C (range: 1.9–3.7) and 2.6&nbsp;°C (range: 1.9–3.6), respectively. All with at least a 66 per cent chance."</ref> Limiting warming to 1.5&nbsp;°C would require halving emissions by 2030 and achieving [[Carbon neutrality|net-zero]] emissions by 2050.<ref>{{harvnb|IPCC SR15 Ch2|2018|pp=95–96}}: "In model pathways with no or limited overshoot of 1.5&nbsp;°C, global net anthropogenic {{CO2}} emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range)"</ref><ref>{{harvnb|IPCC SR15|2018|loc=SPM C.3|p=17}}: "All pathways that limit global warming to 1.5&nbsp;°C with limited or no overshoot project the use of carbon dioxide removal (CDR) on the order of 100–1000 Gt{{CO2}} over the 21st century. CDR would be used to compensate for residual emissions and, in most cases, achieve net negative emissions to return global warming to 1.5&nbsp;°C following a peak (high confidence). CDR deployment of several hundreds of Gt{{CO2}} is subject to multiple feasibility and sustainability constraints (high confidence)."</ref>
Many climate change impacts have been observed in the first decades of the 21st century, with 2023 the warmest on record at +{{convert|1.48|C-change}} since regular tracking began in 1850.<ref>{{cite web |title=2023 confirmed as world's hottest year on record |url=https://www.bbc.com/news/science-environment-67861954 |publisher=[[BBC]] |first1=Mark |last1=Poynting |first2=Erwan |last2=Rivault |access-date=13 January 2024 |date=10 January 2024}}</ref><ref>{{Cite web |date=21 April 2023 |title=Human, economic, environmental toll of climate change on the rise: WMO|url=https://news.un.org/en/story/2023/04/1135852 |access-date=11 April 2024 |publisher=United Nations |language=en}}</ref> Additional warming will increase these impacts and can trigger [[Tipping points in the climate system|tipping points]], such as melting all of the [[Greenland ice sheet]].<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=71}}</ref> Under the 2015 [[Paris Agreement]], nations collectively agreed to keep warming "well under 2&nbsp;°C". However, with pledges made under the Agreement, global warming would still reach about {{convert|2.8|C-change}} by the end of the century.<ref name="UNEP2024">{{harvnb|United Nations Environment Programme|2024|p=XVIII}}: "The full implementation and continuation of the level of mitigation effort implied by unconditional or conditional NDC scenarios lower these projections to 2.8&nbsp;°C (range: 1.9–3.7) and 2.6&nbsp;°C (range: 1.9–3.6), respectively. All with at least a 66 per cent chance."</ref> Limiting warming to 1.5&nbsp;°C would require halving emissions by 2030 and achieving [[Carbon neutrality|net-zero]] emissions by 2050.<ref>{{harvnb|IPCC SR15 Ch2|2018|pp=95–96}}: "In model pathways with no or limited overshoot of 1.5&nbsp;°C, global net anthropogenic {{CO2}} emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range)"</ref><ref>{{harvnb|IPCC SR15|2018|loc=SPM C.3|p=17}}: "All pathways that limit global warming to 1.5&nbsp;°C with limited or no overshoot project the use of carbon dioxide removal (CDR) on the order of 100–1000 Gt{{CO2}} over the 21st century. CDR would be used to compensate for residual emissions and, in most cases, achieve net negative emissions to return global warming to 1.5&nbsp;°C following a peak (high confidence). CDR deployment of several hundreds of Gt{{CO2}} is subject to multiple feasibility and sustainability constraints (high confidence)."</ref>


[[Fossil fuel phase-out|Fossil fuel use can be phased out]] by [[conserving energy]] and switching to energy sources that do not produce significant carbon pollution. These energy sources include [[wind power|wind]], [[solar power|solar]], [[Hydropower|hydro]], and [[nuclear power]].<ref>
[[Fossil fuel phase-out|Fossil fuel use can be phased out]] by [[conserving energy]] and switching to energy sources that do not produce significant carbon pollution. These energy sources include [[wind power|wind]], [[solar power|solar]], [[Hydropower|hydro]], and [[nuclear power]].<ref>
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{{Main|Climate variability and change|Temperature record of the last 2,000 years|Paleoclimatology}}
{{Main|Climate variability and change|Temperature record of the last 2,000 years|Paleoclimatology}}
[[File:Common Era Temperature.svg|thumb|upright=1.35|[[Global surface temperature]] reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue.<ref>{{harvnb|Neukom|Barboza|Erb|Shi|2019b}}.</ref> Directly observed data is in red.<ref name="nasa temperatures">{{cite web |title=Global Annual Mean Surface Air Temperature Change |url=https://data.giss.nasa.gov/gistemp/graphs_v4/ |access-date=23 February 2020 |publisher=[[NASA]]}}</ref>]]
[[File:Common Era Temperature.svg|thumb|upright=1.35|[[Global surface temperature]] reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue.<ref>{{harvnb|Neukom|Barboza|Erb|Shi|2019b}}.</ref> Directly observed data is in red.<ref name="nasa temperatures">{{cite web |title=Global Annual Mean Surface Air Temperature Change |url=https://data.giss.nasa.gov/gistemp/graphs_v4/ |access-date=23 February 2020 |publisher=[[NASA]]}}</ref>]]
Over the last few million years the climate cycled through [[Glacial period|ice ages]]. One of the hotter periods was the [[Last Interglacial]], around 125,000 years ago, where temperatures were between 0.5&nbsp;°C and 1.5&nbsp;°C warmer than before the start of global warming.{{sfn|IPCC AR6 WG1 Ch2|2021|pp=294, 296}} This period saw sea levels 5 to 10 metres higher than today. The most [[Last Glacial Maximum|recent glacial maximum]] 20,000 years ago was some 5–7&nbsp;°C colder. This period has sea levels that were over {{convert|125|m|ft}} lower than today.{{sfn|IPCC AR6 WG1 Ch2|2021|p=366}}
Over the last few million years the climate cycled through [[Glacial period|ice ages]]. One of the hotter periods was the [[Last Interglacial]], around 125,000 years ago, where temperatures were between 0.5&nbsp;°C and 1.5&nbsp;°C warmer than before the start of global warming.{{sfn|IPCC AR6 WG1 Ch2|2021|pp=294, 296}} This period saw sea levels 5 to 10 metres higher than today. The most [[Last Glacial Maximum|recent glacial maximum]] 20,000 years ago was some 5–7&nbsp;°C colder. This period has sea levels that were over {{convert|125|m|ft}} lower than today.{{sfn|IPCC AR6 WG1 Ch2|2021|p=366}}


Temperatures stabilized in the current interglacial period beginning [[holocene|11,700 years ago]].<ref>{{cite journal |last1=Marcott |first1=S. A. |last2=Shakun |first2=J. D. |last3=Clark |first3=P. U. |last4=Mix |first4=A. C. |title=A reconstruction of regional and global temperature for the past 11,300 years |journal=Science |date=2013 |volume=339 |issue=6124 |pages=1198–1201 |doi=10.1126/science.1228026|pmid=23471405 |bibcode=2013Sci...339.1198M }}</ref> This period also saw the start of agriculture.{{sfn|IPCC AR6 WG1 Ch2|2021|p=296}} Historical patterns of warming and cooling, like the [[Medieval Warm Period]] and the [[Little Ice Age]], did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions.<ref>{{harvnb|IPCC AR5 WG1 Ch5|2013|p=386}}</ref><ref>{{harvnb|Neukom|Steiger|Gómez-Navarro|Wang|2019a}}</ref> Climate information for that period comes from [[Proxy (climate)|climate proxies]], such as trees and [[ice core]]s.<ref name="SR15 Ch1 p57">{{harvnb|IPCC SR15 Ch1|2018|p=57}}: "This report adopts the 51-year reference period, 1850–1900 inclusive, assessed as an approximation of pre-industrial levels in AR5&nbsp;... Temperatures rose by 0.0&nbsp;°C–0.2&nbsp;°C from 1720–1800 to 1850–1900"</ref><ref>{{harvnb|Hawkins|Ortega|Suckling|Schurer|2017|p=1844}}</ref>
Temperatures stabilized in the current interglacial period beginning [[holocene|11,700 years ago]].<ref>{{cite journal |last1=Marcott |first1=S. A. |last2=Shakun |first2=J. D. |last3=Clark |first3=P. U. |last4=Mix |first4=A. C. |title=A reconstruction of regional and global temperature for the past 11,300 years |journal=[[Science (journal)|Science]] |year=2013 |volume=339 |issue=6124 |pages=1198–1201 |doi=10.1126/science.1228026|pmid=23471405 |bibcode=2013Sci...339.1198M }}</ref> This period also saw the start of agriculture.{{sfn|IPCC AR6 WG1 Ch2|2021|p=296}} Historical patterns of warming and cooling, like the [[Medieval Warm Period]] and the [[Little Ice Age]], did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions.<ref>{{harvnb|IPCC AR5 WG1 Ch5|2013|p=386}}</ref><ref>{{harvnb|Neukom|Steiger|Gómez-Navarro|Wang|2019a}}</ref> Climate information for that period comes from [[Proxy (climate)|climate proxies]], such as trees and [[ice core]]s.<ref name="SR15 Ch1 p57">{{harvnb|IPCC SR15 Ch1|2018|p=57}}: "This report adopts the 51-year reference period, 1850–1900 inclusive, assessed as an approximation of pre-industrial levels in AR5&nbsp;... Temperatures rose by 0.0&nbsp;°C–0.2&nbsp;°C from 1720–1800 to 1850–1900"</ref><ref>{{harvnb|Hawkins|Ortega|Suckling|Schurer|2017|p=1844}}</ref>


=== Warming since the Industrial Revolution ===
=== Warming since the Industrial Revolution ===
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[[File:1955- Ocean heat content - NOAA.svg|thumb|upright=1.35 |There has been an increase in [[ocean heat content]] during recent decades as the oceans absorb over 90% of the [[Earth's energy budget|heat from global warming]].<ref name=NOAA_NASA_OHC_1957_>''Top 700 meters:'' {{cite web |last1=Lindsey |first1=Rebecca |last2=Dahlman |first2=Luann |title=Climate Change: Ocean Heat Content |url=https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |website=climate.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://archive.today/20231029171303/https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |archive-date=29 October 2023 |date=6 September 2023 |url-status=live }} ● ''Top 2000 meters:'' {{cite web |title=Ocean Warming / Latest Measurement: December 2022 / 345 (± 2) zettajoules since 1955 |url=https://climate.nasa.gov/vital-signs/ocean-warming/ |website=NASA.gov |publisher=National Aeronautics and Space Administration |archive-url=https://web.archive.org/web/20231020033606/https://climate.nasa.gov/vital-signs/ocean-warming/ |archive-date=20 October 2023 |url-status=live}}</ref>]]
[[File:1955- Ocean heat content - NOAA.svg|thumb|upright=1.35 |There has been an increase in [[ocean heat content]] during recent decades as the oceans absorb over 90% of the [[Earth's energy budget|heat from global warming]].<ref name=NOAA_NASA_OHC_1957_>''Top 700 meters:'' {{cite web |last1=Lindsey |first1=Rebecca |last2=Dahlman |first2=Luann |title=Climate Change: Ocean Heat Content |url=https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |website=climate.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://archive.today/20231029171303/https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |archive-date=29 October 2023 |date=6 September 2023 |url-status=live }} ● ''Top 2000 meters:'' {{cite web |title=Ocean Warming / Latest Measurement: December 2022 / 345 (± 2) zettajoules since 1955 |url=https://climate.nasa.gov/vital-signs/ocean-warming/ |website=NASA.gov |publisher=National Aeronautics and Space Administration |archive-url=https://web.archive.org/web/20231020033606/https://climate.nasa.gov/vital-signs/ocean-warming/ |archive-date=20 October 2023 |url-status=live}}</ref>]]
Around 1850 [[thermometer]] records began to provide global coverage.<ref name="AR5 WG1 SPM p4-5">{{Harvnb|IPCC AR5 WG1 Summary for Policymakers|2013|pp=4–5}}: "Global-scale observations from the instrumental era began in the mid-19th century for temperature and other variables&nbsp;... the period 1880 to 2012&nbsp;... multiple independently produced datasets exist."</ref>
Around 1850 [[thermometer]] records began to provide global coverage.<ref name="AR5 WG1 SPM p4-5">{{Harvnb|IPCC AR5 WG1 Summary for Policymakers|2013|pp=4–5}}: "Global-scale observations from the instrumental era began in the mid-19th century for temperature and other variables&nbsp;... the period 1880 to 2012&nbsp;... multiple independently produced datasets exist."</ref>
Between the 18th century and 1970 there was little net warming, as the warming impact of greenhouse gas emissions was offset by cooling from [[sulfur dioxide]] emissions. Sulfur dioxide causes [[acid rain]], but it also produces [[sulfate]] aerosols in the atmosphere, which reflect sunlight and cause so-called [[global dimming]]. After 1970, the increasing accumulation of greenhouse gases and controls on sulfur pollution led to a marked increase in temperature.<ref>{{cite news |url=https://www.washingtonpost.com/climate-environment/2023/12/26/global-warming-accelerating-climate-change/ |title=Is climate change speeding up? Here's what the science says. |last1=Mooney |first1=Chris | last2=Osaka |first2=Shannon |date=26 December 2023 |newspaper=The Washington Post |access-date=18 January 2024}}</ref><ref name="NASA2007">{{cite news |date=15 March 2007 |title=Global 'Sunscreen' Has Likely Thinned, Report NASA Scientists |url=http://www.nasa.gov/centers/goddard/news/topstory/2007/aerosol_dimming.html |publisher=[[NASA]]}}</ref><ref name="Quaas2022" />
Between the 18th century and 1970 there was little net warming, as the warming impact of greenhouse gas emissions was offset by cooling from [[sulfur dioxide]] emissions. Sulfur dioxide causes [[acid rain]], but it also produces [[sulfate]] aerosols in the atmosphere, which reflect sunlight and cause [[global dimming]]. After 1970, the increasing accumulation of greenhouse gases and controls on sulfur pollution led to a marked increase in temperature.<ref>{{cite news |url=https://www.washingtonpost.com/climate-environment/2023/12/26/global-warming-accelerating-climate-change/ |title=Is climate change speeding up? Here's what the science says. |last1=Mooney |first1=Chris | last2=Osaka |first2=Shannon |date=26 December 2023 |newspaper=The Washington Post |access-date=18 January 2024}}</ref><ref name="NASA2007">{{cite news |date=15 March 2007 |title=Global 'Sunscreen' Has Likely Thinned, Report NASA Scientists |url=http://www.nasa.gov/centers/goddard/news/topstory/2007/aerosol_dimming.html |publisher=[[NASA]]}}</ref><ref name="Quaas2022" />
[[File:1880-_Global_surface_temperature_-_heat_map_animation_-_NASA_SVS.webm|thumb|upright=1.35|NASA animation portraying global surface temperature changes from 1880 to 2023. The colour blue denotes cooler temperatures and red denotes warmer temperatures.]]
[[File:1880-_Global_surface_temperature_-_heat_map_animation_-_NASA_SVS.webm|thumb|upright=1.35|NASA animation portraying global surface temperature changes from 1880 to 2023. The colour blue denotes cooler temperatures and red denotes warmer temperatures.]]
Ongoing changes in climate have had no precedent for several thousand years.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=43}}</ref> Multiple independent datasets all show worldwide increases in surface temperature,<ref>{{harvnb|EPA|2016}}: "The U.S. Global Change Research Program, the National Academy of Sciences, and the Intergovernmental Panel on Climate Change (IPCC) have each independently concluded that warming of the climate system in recent decades is "unequivocal". This conclusion is not drawn from any one source of data but is based on multiple lines of evidence, including three worldwide temperature datasets showing nearly identical warming trends as well as numerous other independent indicators of global warming (e.g. rising sea levels, shrinking Arctic sea ice)."</ref> at a rate of around 0.2&nbsp;°C per decade.<ref>{{Harvnb|IPCC SR15 Ch1|2018|p=81}}.</ref> The 2014–2023 decade warmed to an average 1.19&nbsp;°C [1.06–1.30&nbsp;°C] compared to the pre-industrial baseline (1850–1900).<ref>{{harvnb|Forster|Smith|Walsh|Lamb|2024|p=2626}}</ref> Not every single year was warmer than the last: internal [[climate variability]] processes can make any year 0.2&nbsp;°C warmer or colder than the average.<ref name="Samset2020">{{cite journal |last1=Samset |first1=B. H. |last2=Fuglestvedt |first2=J. S. |last3=Lund |first3=M. T. |title=Delayed emergence of a global temperature response after emission mitigation |journal=Nature Communications |date=7 July 2020 |volume=11 |issue=1 |page=3261 |doi=10.1038/s41467-020-17001-1 |pmid=32636367 |pmc=7341748 |bibcode=2020NatCo..11.3261S |quote=At the time of writing, that translated into 2035–2045, where the delay was mostly due to the impacts of the around 0.2 °C of natural, interannual variability of global mean surface air temperature |hdl=11250/2771093 |hdl-access=free }}</ref> From 1998 to 2013, negative phases of two such processes, [[Pacific decadal oscillation|Pacific Decadal Oscillation (PDO)]]<ref name="SeipGrønWang2023PacificDecadalOscillation">{{Cite journal |last1=Seip |first1=Knut L. |last2=Grøn |first2=ø. |last3=Wang |first3=H. |date=31 August 2023 |title=Global lead-lag changes between climate variability series coincide with major phase shifts in the Pacific decadal oscillation |journal=[[Theoretical and Applied Climatology]] |volume=154 |issue=3–4 |language=en |doi=10.1007/s00704-023-04617-8 |issn=0177-798X |pages=1137–1149 |bibcode=2023ThApC.154.1137S |s2cid=261438532 |doi-access=free |hdl=11250/3088837 |hdl-access=free }}</ref> and [[Atlantic multidecadal oscillation|Atlantic Multidecadal Oscillation (AMO)]]<ref>{{Cite journal |last1=Yao |first1=Shuai-Lei |last2=Huang |first2=Gang |last3=Wu |first3=Ren-Guang |last4=Qu |first4=Xia |date=January 2016 |title=The global warming hiatus—a natural product of interactions of a secular warming trend and a multi-decadal oscillation |url=http://link.springer.com/10.1007/s00704-014-1358-x |journal=[[Theoretical and Applied Climatology]] |language=en |volume=123 |issue=1–2 |pages=349–360 |doi=10.1007/s00704-014-1358-x |bibcode=2016ThApC.123..349Y |s2cid=123602825 |issn=0177-798X |access-date=20 September 2023}}</ref> caused a so-called "[[global warming hiatus]]".<ref>{{Cite journal |last1=Xie |first1=Shang-Ping |last2=Kosaka |first2=Yu |date=June 2017 |title=What Caused the Global Surface Warming Hiatus of 1998–2013? |url=http://link.springer.com/10.1007/s40641-017-0063-0 |journal=Current Climate Change Reports |language=en |volume=3 |issue=2 |pages=128–140 |doi=10.1007/s40641-017-0063-0 |bibcode=2017CCCR....3..128X |s2cid=133522627 |issn=2198-6061 |access-date=20 September 2023}}</ref> After the hiatus, the opposite occurred, with years like 2023 exhibiting temperatures well above even the recent average.<ref name="Copernicus2023">{{Cite web |date=21 November 2023 |title=Global temperature exceeds 2&nbsp;°C above pre-industrial average on 17 November |url=https://climate.copernicus.eu/global-temperature-exceeds-2degc-above-pre-industrial-average-17-november |website=[[Copernicus Programme|Copernicus]] |access-date=31 January 2024 |quote=While exceeding the 2&nbsp;°C threshold for a number of days does not mean that we have breached the Paris Agreement targets, the more often that we exceed this threshold, the more serious the cumulative effects of these breaches will become.}}</ref> This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.<ref name="IPCC_AR6_WGI_SPM">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 3−32, doi:10.1017/9781009157896.001.</ref>{{rp|5}}<ref>{{Cite web |last=McGrath |first=Matt |date=17 May 2023 |title=Global warming set to break key 1.5C limit for first time |url=https://www.bbc.com/news/science-environment-65602293 |website=[[BBC News]] |access-date=31 January 2024 |quote=The researchers stress that temperatures would have to stay at or above 1.5C for 20 years to be able to say the Paris agreement threshold had been passed. }}</ref>
Ongoing changes in climate have had no precedent for several thousand years.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=43}}</ref> Multiple independent datasets all show worldwide increases in surface temperature,<ref>{{harvnb|EPA|2016}}: "The U.S. Global Change Research Program, the National Academy of Sciences, and the Intergovernmental Panel on Climate Change (IPCC) have each independently concluded that warming of the climate system in recent decades is "unequivocal". This conclusion is not drawn from any one source of data but is based on multiple lines of evidence, including three worldwide temperature datasets showing nearly identical warming trends as well as numerous other independent indicators of global warming (e.g. rising sea levels, shrinking Arctic sea ice)."</ref> at a rate of around 0.2&nbsp;°C per decade.<ref>{{Harvnb|IPCC SR15 Ch1|2018|p=81}}.</ref> The 2014–2023 decade warmed to an average 1.19&nbsp;°C [1.06–1.30&nbsp;°C] compared to the pre-industrial baseline (1850–1900).<ref>{{harvnb|Forster|Smith|Walsh|Lamb|2024|p=2626}}</ref> Not every single year was warmer than the last: internal [[climate variability]] processes can make any year 0.2&nbsp;°C warmer or colder than the average.<ref name="Samset2020">{{cite journal |last1=Samset |first1=B. H. |last2=Fuglestvedt |first2=J. S. |last3=Lund |first3=M. T. |title=Delayed emergence of a global temperature response after emission mitigation |journal=Nature Communications |date=7 July 2020 |volume=11 |issue=1 |page=3261 |doi=10.1038/s41467-020-17001-1 |pmid=32636367 |pmc=7341748 |bibcode=2020NatCo..11.3261S |quote=At the time of writing, that translated into 2035–2045, where the delay was mostly due to the impacts of the around 0.2 °C of natural, interannual variability of global mean surface air temperature |hdl=11250/2771093 |hdl-access=free }}</ref> From 1998 to 2013, negative phases of two such processes, [[Pacific decadal oscillation|Pacific Decadal Oscillation (PDO)]]<ref name="SeipGrønWang2023PacificDecadalOscillation">{{Cite journal |last1=Seip |first1=Knut L. |last2=Grøn |first2=ø. |last3=Wang |first3=H. |date=31 August 2023 |title=Global lead-lag changes between climate variability series coincide with major phase shifts in the Pacific decadal oscillation |journal=[[Theoretical and Applied Climatology]] |volume=154 |issue=3–4 |language=en |doi=10.1007/s00704-023-04617-8 |issn=0177-798X |pages=1137–1149 |bibcode=2023ThApC.154.1137S |s2cid=261438532 |doi-access=free |hdl=11250/3088837 |hdl-access=free }}</ref> and [[Atlantic multidecadal oscillation|Atlantic Multidecadal Oscillation (AMO)]]<ref>{{Cite journal |last1=Yao |first1=Shuai-Lei |last2=Huang |first2=Gang |last3=Wu |first3=Ren-Guang |last4=Qu |first4=Xia |date=January 2016 |title=The global warming hiatus—a natural product of interactions of a secular warming trend and a multi-decadal oscillation |url=http://link.springer.com/10.1007/s00704-014-1358-x |journal=[[Theoretical and Applied Climatology]] |language=en |volume=123 |issue=1–2 |pages=349–360 |doi=10.1007/s00704-014-1358-x |bibcode=2016ThApC.123..349Y |s2cid=123602825 |issn=0177-798X |access-date=20 September 2023}}</ref> caused a short slower period of warming called the "[[global warming hiatus]]".<ref>{{Cite journal |last1=Xie |first1=Shang-Ping |last2=Kosaka |first2=Yu |date=June 2017 |title=What Caused the Global Surface Warming Hiatus of 1998–2013? |url=http://link.springer.com/10.1007/s40641-017-0063-0 |journal=Current Climate Change Reports |language=en |volume=3 |issue=2 |pages=128–140 |doi=10.1007/s40641-017-0063-0 |bibcode=2017CCCR....3..128X |s2cid=133522627 |issn=2198-6061 |access-date=20 September 2023}}</ref> After the "hiatus", the opposite occurred, with years like 2023 exhibiting temperatures well above even the recent average.<ref name="Copernicus2023">{{Cite web |date=21 November 2023 |title=Global temperature exceeds 2&nbsp;°C above pre-industrial average on 17 November |url=https://climate.copernicus.eu/global-temperature-exceeds-2degc-above-pre-industrial-average-17-november |website=[[Copernicus Programme|Copernicus]] |access-date=31 January 2024 |quote=While exceeding the 2&nbsp;°C threshold for a number of days does not mean that we have breached the Paris Agreement targets, the more often that we exceed this threshold, the more serious the cumulative effects of these breaches will become.}}</ref> This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.<ref name="IPCC_AR6_WGI_SPM">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 3−32, doi:10.1017/9781009157896.001.</ref>{{rp|5}}<ref>{{Cite web |last=McGrath |first=Matt |date=17 May 2023 |title=Global warming set to break key 1.5C limit for first time |url=https://www.bbc.com/news/science-environment-65602293 |website=[[BBC News]] |access-date=31 January 2024 |quote=The researchers stress that temperatures would have to stay at or above 1.5C for 20 years to be able to say the Paris agreement threshold had been passed. }}</ref>


A wide range of other observations reinforce the evidence of warming.<ref>{{harvnb|Kennedy|Thorne|Peterson|Ruedy|2010|p=S26}}. Figure 2.5.</ref>{{sfn|Loeb et al.|2021}} The upper atmosphere is cooling, because [[greenhouse gas]]es are trapping heat near the Earth's surface, and so less heat is radiating into space.<ref>{{cite web |url=https://earthobservatory.nasa.gov/features/GlobalWarming |title=Global Warming |date=3 June 2010 |publisher=[[NASA JPL]] |access-date=11 September 2020 |quote=Satellite measurements show warming in the troposphere but cooling in the stratosphere. This vertical pattern is consistent with global warming due to increasing greenhouse gases but inconsistent with warming from natural causes.}}</ref> Warming reduces average snow cover and [[retreat of glaciers since 1850|forces the retreat of glaciers]]. At the same time, warming also causes [[Effects of climate change on the water cycle|greater evaporation from the oceans]], leading to more [[specific humidity|atmospheric humidity]], more and heavier [[precipitation]].<ref>{{harvnb|Kennedy|Thorne|Peterson|Ruedy|2010|pp=S26, S59–S60}}</ref><ref>{{harvnb|USGCRP Chapter 1|2017|p=35}}</ref> Plants are [[flowering]] earlier in spring, and thousands of animal species have been permanently moving to cooler areas.<ref>{{harvnb|IPCC AR6 WG2|2022|pp=257–260}}</ref>
A wide range of other observations reinforce the evidence of warming.<ref>{{harvnb|Kennedy|Thorne|Peterson|Ruedy|2010|p=S26}}. Figure 2.5.</ref>{{sfn|Loeb et al.|2021}} The upper atmosphere is cooling, because [[greenhouse gas]]es are trapping heat near the Earth's surface, and so less heat is radiating into space.<ref>{{cite web |url=https://earthobservatory.nasa.gov/features/GlobalWarming |title=Global Warming |date=3 June 2010 |publisher=[[NASA JPL]] |access-date=11 September 2020 |quote=Satellite measurements show warming in the troposphere but cooling in the stratosphere. This vertical pattern is consistent with global warming due to increasing greenhouse gases but inconsistent with warming from natural causes.}}</ref> Warming reduces average snow cover and [[retreat of glaciers since 1850|forces the retreat of glaciers]]. At the same time, warming also causes [[Effects of climate change on the water cycle|greater evaporation from the oceans]], leading to more [[specific humidity|atmospheric humidity]], more and heavier [[precipitation]].<ref>{{harvnb|Kennedy|Thorne|Peterson|Ruedy|2010|pp=S26, S59–S60}}</ref><ref>{{harvnb|USGCRP Chapter 1|2017|p=35}}</ref> Plants are [[flowering]] earlier in spring, and thousands of animal species have been permanently moving to cooler areas.<ref>{{harvnb|IPCC AR6 WG2|2022|pp=257–260}}</ref>
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=== Future global temperatures ===
=== Future global temperatures ===
[[File:Projected Change in Temperatures by 2090.svg|upright=1.35|thumb|[[Coupled Model Intercomparison Project#CMIP Phase 6|CMIP6]] multi-model projections of [[global surface temperature]] changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes.<ref name="UNEP2024" /><ref name="Schuur2022">{{Cite journal |last1=Schuur |first1=Edward A.G. |last2=Abbott |first2=Benjamin W. |last3=Commane |first3=Roisin |last4=Ernakovich |first4=Jessica |last5=Euskirchen |first5=Eugenie |last6=Hugelius |first6=Gustaf |last7=Grosse |first7=Guido |last8=Jones |first8=Miriam |last9=Koven |first9=Charlie |last10=Leshyk |first10=Victor |last11=Lawrence |first11=David |last12=Loranty |first12=Michael M. |last13=Mauritz |first13=Marguerite |last14=Olefeldt |first14=David |last15=Natali |first15=Susan |last16=Rodenhizer |first16=Heidi |last17=Salmon |first17=Verity |last18=Schädel |first18=Christina |last19=Strauss |first19=Jens |last20=Treat |first20=Claire |last21=Turetsky |first21=Merritt |year=2022 |title=Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic |journal=Annual Review of Environment and Resources |volume=47 |pages=343–371 |doi=10.1146/annurev-environ-012220-011847 |quote="Medium-range estimates of Arctic carbon emissions could result from moderate climate emission mitigation policies that keep global warming below 3&nbsp;°C (e.g., RCP4.5). This global warming level most closely matches country emissions reduction pledges made for the Paris Climate Agreement..." |doi-access=free |bibcode=2022ARER...47..343S }}</ref><ref name="Phiddian2022">{{Cite web |last=Phiddian |first=Ellen |date=5 April 2022 |title=Explainer: IPCC Scenarios |url=https://cosmosmagazine.com/earth/climate/explainer-ipcc-scenarios/ |website=[[Cosmos (magazine)|Cosmos]] |access-date=30 September 2023 |quote="The IPCC doesn't make projections about which of these scenarios is more likely, but other researchers and modellers can. [[The Australian Academy of Science]], for instance, released a report last year stating that our current emissions trajectory had us headed for a 3&nbsp;°C warmer world, roughly in line with the middle scenario. [[Climate Action Tracker]] predicts 2.5 to 2.9&nbsp;°C of warming based on current policies and action, with pledges and government agreements taking this to 2.1&nbsp;°C.}}</ref>]]
[[File:Projected Change in Temperatures by 2090.svg|upright=1.35|thumb|[[Coupled Model Intercomparison Project#CMIP Phase 6|CMIP6]] multi-model projections of [[global surface temperature]] changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes.<ref name="UNEP2024" /><ref name="Schuur2022">{{Cite journal |last1=Schuur |first1=Edward A. G. |last2=Abbott |first2=Benjamin W. |last3=Commane |first3=Roisin |last4=Ernakovich |first4=Jessica |last5=Euskirchen |first5=Eugenie |last6=Hugelius |first6=Gustaf |last7=Grosse |first7=Guido |last8=Jones |first8=Miriam |last9=Koven |first9=Charlie |last10=Leshyk |first10=Victor |last11=Lawrence |first11=David |last12=Loranty |first12=Michael M. |last13=Mauritz |first13=Marguerite |last14=Olefeldt |first14=David |last15=Natali |first15=Susan |year=2022 |title=Permafrost and Climate Change: Carbon Cycle Feedbacks From the Warming Arctic |journal=Annual Review of Environment and Resources |volume=47 |pages=343–371 |bibcode=2022ARER...47..343S |doi=10.1146/annurev-environ-012220-011847 |quote="Medium-range estimates of Arctic carbon emissions could result from moderate climate emission mitigation policies that keep global warming below 3&nbsp;°C (e.g., RCP4.5). This global warming level most closely matches country emissions reduction pledges made for the Paris Climate Agreement..." |doi-access=free |last16=Rodenhizer |first16=Heidi |last17=Salmon |first17=Verity |last18=Schädel |first18=Christina |last19=Strauss |first19=Jens |last20=Treat |first20=Claire |last21=Turetsky |first21=Merritt}}</ref><ref name="Phiddian2022">{{Cite web |last=Phiddian |first=Ellen |date=5 April 2022 |title=Explainer: IPCC Scenarios |url=https://cosmosmagazine.com/earth/climate/explainer-ipcc-scenarios/ |website=[[Cosmos (magazine)|Cosmos]] |access-date=30 September 2023 |quote="The IPCC doesn't make projections about which of these scenarios is more likely, but other researchers and modellers can. [[The Australian Academy of Science]], for instance, released a report last year stating that our current emissions trajectory had us headed for a 3&nbsp;°C warmer world, roughly in line with the middle scenario. [[Climate Action Tracker]] predicts 2.5 to 2.9&nbsp;°C of warming based on current policies and action, with pledges and government agreements taking this to 2.1&nbsp;°C.}}</ref>]]
The [[World Meteorological Organization]] estimates there is an 80% chance that global temperatures will exceed 1.5&nbsp;°C warming for at least one year between 2024 and 2028. The chance of the 5-year average being above 1.5&nbsp;°C is almost half.{{sfn|WMO|2024b|p=2}}
The [[World Meteorological Organization]] estimates there is an 80% chance that global temperatures will exceed 1.5&nbsp;°C warming for at least one year between 2024 and 2028. The chance of the 5-year average being above 1.5&nbsp;°C is almost half.{{sfn|WMO|2024b|p=2}}


The IPCC expects the 20-year average global temperature to exceed +1.5&nbsp;°C in the early 2030s.<ref>{{Cite web |date=7 August 2021 |title=Climate Change 2021 - The Physical Science Basis |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf#page=955 |url-status=live |archive-url=https://web.archive.org/web/20240405072633/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf#page=955 |archive-date=5 April 2024 |website=Intergovernmental Panel on Climate Change |id=IPCC AR6 WGI}}</ref> The [[IPCC Sixth Assessment Report]] (2021) included projections that by 2100 global warming is very likely to reach 1.0–1.8&nbsp;°C under a [[Shared Socioeconomic Pathways#SSP1: Sustainability (Taking the Green Road)|scenario with very low emissions of greenhouse gases]], 2.1–3.5&nbsp;°C under an [[Shared Socioeconomic Pathways#SSP3: Regional rivalry (A Rocky Road)|intermediate emissions scenario]],
The IPCC expects the 20-year average global temperature to exceed +1.5&nbsp;°C in the early 2030s.<ref>{{Cite web |date=7 August 2021 |title=Climate Change 2021 - The Physical Science Basis |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf#page=955 |url-status=live |archive-url=https://web.archive.org/web/20240405072633/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf#page=955 |archive-date=5 April 2024 |website=Intergovernmental Panel on Climate Change |id=IPCC AR6 WGI}}</ref> The [[IPCC Sixth Assessment Report]] (2021) included projections that by 2100 global warming is very likely to reach 1.0–1.8&nbsp;°C under a [[Shared Socioeconomic Pathways#SSP1: Sustainability (Taking the Green Road)|scenario with very low emissions of greenhouse gases]], 2.1–3.5&nbsp;°C under an [[Shared Socioeconomic Pathways#SSP3: Regional rivalry (A Rocky Road)|intermediate emissions scenario]],
or 3.3–5.7&nbsp;°C under [[Shared Socioeconomic Pathways#SSP5: Fossil-Fueled Development (Taking the Highway)|a very high emissions scenario]].<ref>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|p=SPM-17}}</ref> The warming will continue past 2100 in the intermediate and high emission scenarios,<ref name="Meinshausen2011">{{Cite journal |last1=Meinshausen |first1=Malte |last2=Smith |first2=S. J. |last3=Calvin |first3=K. |last4=Daniel |first4=J. S. |last5=Kainuma |first5=M. L. T. |last6=Lamarque |first6=J-F. |last7=Matsumoto |first7=K. |last8=Montzka |first8=S. A. |last9=Raper |first9=S. C. B. |last10=Riahi |first10=K. |last11=Thomson |first11=A. |last12=Velders |first12=G. J. M. |last13=van Vuuren |first13=D.P. P. |date=2011 |title=The RCP greenhouse gas concentrations and their extensions from 1765 to 2300 |journal=Climatic Change |language=en |volume=109 |issue=1–2 |pages=213–241 |doi=10.1007/s10584-011-0156-z |bibcode=2011ClCh..109..213M |issn=0165-0009|doi-access=free }}</ref><ref name="Lyon2021">{{cite journal |last1=Lyon |first1=Christopher |last2=Saupe |first2=Erin E. |last3=Smith |first3=Christopher J. |last4=Hill |first4=Daniel J. |last5=Beckerman |first5=Andrew P. |last6=Stringer |first6=Lindsay C. |last7=Marchant |first7=Robert |last8=McKay |first8=James |last9=Burke |first9=Ariane |last10=O'Higgins |first10=Paul |last11=Dunhill |first11=Alexander M. |last12=Allen |first12=Bethany J. |last13=Riel-Salvatore |first13=Julien |last14=Aze |first14=Tracy |year=2021 |title=Climate change research and action must look beyond 2100 |journal=Global Change Biology |language=en |volume=28 |issue=2 |pages=349–361 |doi=10.1111/gcb.15871 |issn=1365-2486 |pmid=34558764 |s2cid=237616583 |doi-access=free|hdl=20.500.11850/521222 |hdl-access=free }}</ref> with future projections of global surface temperatures by year 2300 being similar to millions of years ago.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|pp=43–44}}</ref>
or 3.3–5.7&nbsp;°C under [[Shared Socioeconomic Pathways#SSP5: Fossil-Fueled Development (Taking the Highway)|a very high emissions scenario]].<ref>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|p=SPM-17}}</ref> The warming will continue past 2100 in the intermediate and high emission scenarios,<ref name="Meinshausen2011">{{Cite journal |last1=Meinshausen |first1=Malte |last2=Smith |first2=S. J. |last3=Calvin |first3=K. |last4=Daniel |first4=J. S. |last5=Kainuma |first5=M. L. T. |last6=Lamarque |first6=J-F. |last7=Matsumoto |first7=K. |last8=Montzka |first8=S. A. |last9=Raper |first9=S. C. B. |last10=Riahi |first10=K. |last11=Thomson |first11=A. |last12=Velders |first12=G. J. M. |last13=van Vuuren |first13=D.P. P. |year=2011 |title=The RCP greenhouse gas concentrations and their extensions from 1765 to 2300 |journal=Climatic Change |language=en |volume=109 |issue=1–2 |pages=213–241 |doi=10.1007/s10584-011-0156-z |bibcode=2011ClCh..109..213M |issn=0165-0009|doi-access=free }}</ref><ref name="Lyon2021">{{cite journal |last1=Lyon |first1=Christopher |last2=Saupe |first2=Erin E. |last3=Smith |first3=Christopher J. |last4=Hill |first4=Daniel J. |last5=Beckerman |first5=Andrew P. |last6=Stringer |first6=Lindsay C. |last7=Marchant |first7=Robert |last8=McKay |first8=James |last9=Burke |first9=Ariane |last10=O'Higgins |first10=Paul |last11=Dunhill |first11=Alexander M. |last12=Allen |first12=Bethany J. |last13=Riel-Salvatore |first13=Julien |last14=Aze |first14=Tracy |year=2021 |title=Climate change research and action must look beyond 2100 |journal=Global Change Biology |language=en |volume=28 |issue=2 |pages=349–361 |doi=10.1111/gcb.15871 |issn=1365-2486 |pmid=34558764 |s2cid=237616583 |doi-access=free|hdl=20.500.11850/521222 |hdl-access=free }}</ref> with future projections of global surface temperatures by year 2300 being similar to millions of years ago.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|pp=43–44}}</ref>


The remaining [[carbon budget]] for staying beneath certain temperature increases is determined by modelling the carbon cycle and [[climate sensitivity]] to greenhouse gases.<ref>{{harvnb|Rogelj|Forster|Kriegler|Smith|2019}}</ref> According to [[UNEP]], global warming can be kept below 1.5&nbsp;°C with a 50% chance if emissions after 2023 do not exceed 200 gigatonnes of {{CO2}}. This corresponds to around 4 years of current emissions. To stay under 2.0&nbsp;°C, the carbon budget is 900 gigatonnes of {{CO2}}, or 16 years of current emissions.{{sfn|United Nations Environment Programme|2024|pp=XI, XVII}}
The remaining [[carbon budget]] for staying beneath certain temperature increases is determined by modelling the carbon cycle and [[climate sensitivity]] to greenhouse gases.<ref>{{harvnb|Rogelj|Forster|Kriegler|Smith|2019}}</ref> According to [[UNEP]], global warming can be kept below 1.5&nbsp;°C with a 50% chance if emissions after 2023 do not exceed 200 gigatonnes of {{CO2}}. This corresponds to around 4 years of current emissions. To stay under 2.0&nbsp;°C, the carbon budget is 900 gigatonnes of {{CO2}}, or 16 years of current emissions.{{sfn|United Nations Environment Programme|2024|pp=XI, XVII}}
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[[File:CO2 Emissions by Source Since 1880.svg|thumb|upright=1.35|right|The [[Global Carbon Project]] shows how additions to {{CO2}} since 1880 have been caused by different sources ramping up one after another.]]
[[File:CO2 Emissions by Source Since 1880.svg|thumb|upright=1.35|right|The [[Global Carbon Project]] shows how additions to {{CO2}} since 1880 have been caused by different sources ramping up one after another.]]


Global anthropogenic greenhouse gas emissions in 2019 were [[Global warming potential|equivalent to]] 59&nbsp;billion tonnes of {{CO2}}. Of these emissions, 75% was {{CO2}}, 18% was [[methane]], 4% was nitrous oxide, and 2% was [[fluorinated gases]].{{sfn|IPCC AR6 WG3 Summary for Policymakers|2022|loc=Figure SPM.1}} {{CO2}} emissions primarily come from burning fossil fuels to provide energy for [[transport]], manufacturing, [[Heating#Energy sources|heating]], and electricity.<ref name="Our World in Data-2020"/> Additional {{CO2}} emissions come from [[deforestation and climate change|deforestation]] and [[Industrial processes#Chemical processes by main basic material|industrial processes]], which include the {{CO2}} released by the chemical reactions for [[Cement#Chemistry|making cement]], [[Blast furnace#Process engineering and chemistry|steel]], [[Hall–Héroult process|aluminum]], and [[haber process|fertilizer]].<ref>{{harvnb|Olivier|Peters|2019|p=17}}</ref><ref>{{harvnb|Our World in Data, 18 September|2020}}; {{harvnb|EPA|2020}}: "Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials."</ref><ref>{{cite web|title=Redox, extraction of iron and transition metals|url=https://www.bbc.co.uk/bitesize/guides/zv7f3k7/revision/2|quote=Hot air (oxygen) reacts with the coke (carbon) to produce carbon dioxide and heat energy to heat up the furnace. Removing impurities: The calcium carbonate in the limestone thermally decomposes to form calcium oxide. calcium carbonate → calcium oxide + carbon dioxide}}</ref><ref>{{harvnb|Kvande|2014}}: "Carbon dioxide gas is formed at the anode, as the carbon anode is consumed upon reaction of carbon with the oxygen ions from the alumina ({{chem2|Al2O3}}). Formation of carbon dioxide is unavoidable as long as carbon anodes are used, and it is of great concern because {{CO2}} is a greenhouse gas."</ref> Methane emissions [[enteric fermentation|come from livestock]], manure, [[Environmental impact of rice cultivation|rice cultivation]], landfills, wastewater, and [[coal seam gas|coal mining]], as well as [[fugitive gas emissions|oil and gas extraction]].<ref>{{harvnb|EPA|2020}}</ref><ref>{{harvnb|Global Methane Initiative|2020}}: "Estimated Global Anthropogenic Methane Emissions by Source, 2020: [[Enteric fermentation]] (27%), Manure Management (3%), Coal Mining (9%), [[Municipal Solid Waste]] (11%), Oil & Gas (24%), [[Wastewater]] (7%), [[Rice|Rice Cultivation]] (7%)."</ref> Nitrous oxide emissions largely come from the microbial decomposition of [[fertilizer]].<ref>{{harvnb|EPA|2019}}: "Agricultural activities, such as fertilizer use, are the primary source of {{N2O}} emissions."</ref><ref>{{harvnb|Davidson|2009}}: "2.0% of manure nitrogen and 2.5% of fertilizer nitrogen was converted to nitrous oxide between 1860 and 2005; these percentage contributions explain the entire pattern of increasing nitrous oxide concentrations over this period."</ref>
Global human-caused greenhouse gas emissions in 2019 were [[Global warming potential|equivalent to]] 59&nbsp;billion tonnes of {{CO2}}. Of these emissions, 75% was {{CO2}}, 18% was [[methane]], 4% was nitrous oxide, and 2% was [[fluorinated gases]].{{sfn|IPCC AR6 WG3 Summary for Policymakers|2022|loc=Figure SPM.1}} {{CO2}} emissions primarily come from burning fossil fuels to provide energy for [[transport]], manufacturing, [[Heating#Energy sources|heating]], and electricity.<ref name="Our World in Data-2020"/> Additional {{CO2}} emissions come from [[deforestation and climate change|deforestation]] and [[Industrial processes#Chemical processes by main basic material|industrial processes]], which include the {{CO2}} released by the chemical reactions for [[Cement#Chemistry|making cement]], [[Blast furnace#Process engineering and chemistry|steel]], [[Hall–Héroult process|aluminum]], and [[haber process|fertilizer]].<ref>{{harvnb|Olivier|Peters|2019|p=17}}</ref><ref>{{harvnb|Our World in Data, 18 September|2020}}; {{harvnb|EPA|2020}}: "Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials."</ref><ref>{{cite web|title=Redox, extraction of iron and transition metals|url=https://www.bbc.co.uk/bitesize/guides/zv7f3k7/revision/2|quote=Hot air (oxygen) reacts with the coke (carbon) to produce carbon dioxide and heat energy to heat up the furnace. Removing impurities: The calcium carbonate in the limestone thermally decomposes to form calcium oxide. calcium carbonate → calcium oxide + carbon dioxide}}</ref><ref>{{harvnb|Kvande|2014}}: "Carbon dioxide gas is formed at the anode, as the carbon anode is consumed upon reaction of carbon with the oxygen ions from the alumina ({{chem2|Al2O3}}). Formation of carbon dioxide is unavoidable as long as carbon anodes are used, and it is of great concern because {{CO2}} is a greenhouse gas."</ref> Methane emissions [[enteric fermentation|come from livestock]], manure, [[Environmental impact of rice cultivation|rice cultivation]], landfills, wastewater, and [[coal seam gas|coal mining]], as well as [[fugitive gas emissions|oil and gas extraction]].<ref>{{harvnb|EPA|2020}}</ref><ref>{{harvnb|Global Methane Initiative|2020}}: "Estimated Global Anthropogenic Methane Emissions by Source, 2020: [[Enteric fermentation]] (27%), Manure Management (3%), Coal Mining (9%), [[Municipal Solid Waste]] (11%), Oil & Gas (24%), [[Wastewater]] (7%), [[Rice|Rice Cultivation]] (7%)."</ref> Nitrous oxide emissions largely come from the microbial decomposition of [[fertilizer]].<ref>{{harvnb|EPA|2019}}: "Agricultural activities, such as fertilizer use, are the primary source of {{N2O}} emissions."</ref><ref>{{harvnb|Davidson|2009}}: "2.0% of manure nitrogen and 2.5% of fertilizer nitrogen was converted to nitrous oxide between 1860 and 2005; these percentage contributions explain the entire pattern of increasing nitrous oxide concentrations over this period."</ref>


While methane only lasts in the atmosphere for an average of 12 years,<ref>{{cite web |title=Understanding methane emissions |publisher=International Energy Agency |url=https://www.iea.org/reports/global-methane-tracker-2023/understanding-methane-emissions}}</ref> {{CO2}} lasts much longer. The Earth's surface absorbs {{CO2}} as part of the [[carbon cycle]]. While plants on land and in the ocean absorb most excess emissions of {{CO2}} every year, that {{CO2}} is returned to the atmosphere when biological matter is digested, burns, or decays.<ref name="nasacc">{{cite web|last1=Riebeek|first1=Holli|title=The Carbon Cycle|url=http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features|website=Earth Observatory|publisher=NASA|access-date=5 April 2018|date=16 June 2011|archive-url=https://web.archive.org/web/20160305010126/http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features|archive-date=5 March 2016|url-status=live}}</ref> Land-surface [[carbon sink]] processes, such as [[carbon fixation]] in the soil and photosynthesis, remove about 29% of annual global {{CO2}} emissions.<ref>{{Harvnb|IPCC SRCCL Summary for Policymakers|2019|p=10}}</ref> The ocean has absorbed 20 to 30% of emitted {{CO2}} over the last two decades.<ref>{{harvnb|IPCC SROCC Ch5|2019|p=450}}.</ref> {{CO2}} is only removed from the atmosphere for the long term when it is stored in the Earth's crust, which is a process that can take millions of years to complete.<ref name="nasacc" />
While methane only lasts in the atmosphere for an average of 12 years,<ref>{{cite web |title=Understanding methane emissions |publisher=International Energy Agency |url=https://www.iea.org/reports/global-methane-tracker-2023/understanding-methane-emissions}}</ref> {{CO2}} lasts much longer. The Earth's surface absorbs {{CO2}} as part of the [[carbon cycle]]. While plants on land and in the ocean absorb most excess emissions of {{CO2}} every year, that {{CO2}} is returned to the atmosphere when biological matter is digested, burns, or decays.<ref name="nasacc">{{cite web|last1=Riebeek|first1=Holli|title=The Carbon Cycle|url=http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features|website=Earth Observatory|publisher=NASA|access-date=5 April 2018|date=16 June 2011|archive-url=https://web.archive.org/web/20160305010126/http://earthobservatory.nasa.gov/Features/CarbonCycle/?src=eoa-features|archive-date=5 March 2016|url-status=live}}</ref> Land-surface [[carbon sink]] processes, such as [[carbon fixation]] in the soil and photosynthesis, remove about 29% of annual global {{CO2}} emissions.<ref>{{Harvnb|IPCC SRCCL Summary for Policymakers|2019|p=10}}</ref> The ocean has absorbed 20 to 30% of emitted {{CO2}} over the last two decades.<ref>{{harvnb|IPCC SROCC Ch5|2019|p=450}}.</ref> {{CO2}} is only removed from the atmosphere for the long term when it is stored in the Earth's crust, which is a process that can take millions of years to complete.<ref name="nasacc" />
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=== Other factors ===
=== Other factors ===
==== Aerosols and clouds ====
==== Aerosols and clouds ====
Air pollution, in the form of [[Particulates#Climate effects|aerosols, affects the climate]] on a large scale.<ref>{{Harvnb|Haywood|2016|p=456}}; {{harvnb|McNeill|2017}}; {{harvnb|Samset|Sand|Smith|Bauer|2018}}.</ref> Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of [[irradiance|sunlight reaching the Earth's surface]] was observed. This phenomenon is popularly known as ''[[global dimming]]'',<ref>{{harvnb|IPCC AR5 WG1 Ch2|2013|p=183}}.</ref> and is primarily attributed to [[sulfate]] aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like [[coal]] and [[bunker fuel]].<ref name="Quaas2022" /> Smaller contributions come from [[black carbon]] (from combustion of fossil fuels and biomass), and from anthropogenic dust.<ref>{{harvnb|He|Wang|Zhou|Wild|2018}}; {{Harvnb|Storelvmo|Phillips|Lohmann|Leirvik|2016}}</ref><ref>{{Cite web |date=18 February 2021 |title=Aerosol pollution has caused decades of global dimming |url=https://news.agu.org/press-release/aerosol-pollution-caused-decades-of-global-dimming/ |website=[[American Geophysical Union]] |access-date=18 December 2023 |archive-url=https://web.archive.org/web/20230327143716/https://news.agu.org/press-release/aerosol-pollution-caused-decades-of-global-dimming/ |archive-date=27 March 2023 }}</ref><ref>{{Cite journal |title=Double Trouble of Air Pollution by Anthropogenic Dust |year=2022 |doi=10.1021/acs.est.1c04779 |last1=Xia |first1=Wenwen |last2=Wang |first2=Yong |last3=Chen |first3=Siyu |last4=Huang |first4=Jianping |last5=Wang |first5=Bin |last6=Zhang |first6=Guang J. |last7=Zhang |first7=Yue |last8=Liu |first8=Xiaohong |last9=Ma |first9=Jianmin |last10=Gong |first10=Peng |last11=Jiang |first11=Yiquan |last12=Wu |first12=Mingxuan |last13=Xue |first13=Jinkai |last14=Wei |first14=Linyi |last15=Zhang |first15=Tinghan |journal=Environmental Science & Technology |volume=56 |issue=2 |pages=761–769 |pmid=34941248 |bibcode=2022EnST...56..761X |hdl=10138/341962 |s2cid=245445736 |doi-access=free }}</ref> Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.<ref>{{harvnb|Wild|Gilgen|Roesch|Ohmura|2005}}; {{Harvnb|Storelvmo|Phillips|Lohmann|Leirvik|2016}}; {{harvnb|Samset|Sand|Smith|Bauer|2018}}.</ref><ref name="Quaas2022">{{Cite journal |last1=Quaas |first1=Johannes |last2=Jia |first2=Hailing |last3=Smith |first3=Chris |last4=Albright |first4=Anna Lea |last5=Aas |first5=Wenche |last6=Bellouin |first6=Nicolas |last7=Boucher |first7=Olivier |last8=Doutriaux-Boucher |first8=Marie |last9=Forster |first9=Piers M. |last10=Grosvenor |first10=Daniel |last11=Jenkins |first11=Stuart |last12=Klimont |first12=Zbigniew |last13=Loeb |first13=Norman G. |last14=Ma |first14=Xiaoyan |last15=Naik |first15=Vaishali |last16=Paulot |first16=Fabien |last17=Stier |first17=Philip |last18=Wild |first18=Martin |last19=Myhre |first19=Gunnar |last20=Schulz |first20=Michael |date=21 September 2022 |title=Robust evidence for reversal of the trend in aerosol effective climate forcing |url=https://acp.copernicus.org/articles/22/12221/2022/ |journal=Atmospheric Chemistry and Physics |volume=22 |issue=18 |pages=12221–12239 |language=en |doi=10.5194/acp-22-12221-2022 |s2cid=252446168 |hdl=20.500.11850/572791 |hdl-access=free |doi-access=free |bibcode=2022ACP....2212221Q }}</ref>
Air pollution, in the form of [[Particulates#Climate effects|aerosols, affects the climate]] on a large scale.<ref>{{Harvnb|Haywood|2016|p=456}}; {{harvnb|McNeill|2017}}; {{harvnb|Samset|Sand|Smith|Bauer|2018}}.</ref> Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of [[irradiance|sunlight reaching the Earth's surface]] was observed. This phenomenon is popularly known as ''[[global dimming]]'',<ref>{{harvnb|IPCC AR5 WG1 Ch2|2013|p=183}}.</ref> and is primarily attributed to [[sulfate]] aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like [[coal]] and [[bunker fuel]].<ref name="Quaas2022" /> Smaller contributions come from [[black carbon]] (from combustion of fossil fuels and biomass), and from dust.<ref>{{harvnb|He|Wang|Zhou|Wild|2018}}; {{Harvnb|Storelvmo|Phillips|Lohmann|Leirvik|2016}}</ref><ref>{{Cite web |date=18 February 2021 |title=Aerosol pollution has caused decades of global dimming |url=https://news.agu.org/press-release/aerosol-pollution-caused-decades-of-global-dimming/ |website=[[American Geophysical Union]] |access-date=18 December 2023 |archive-url=https://web.archive.org/web/20230327143716/https://news.agu.org/press-release/aerosol-pollution-caused-decades-of-global-dimming/ |archive-date=27 March 2023 }}</ref><ref>{{Cite web |last=Monroe |first=Robert |date=2023-01-20 |title=Increased Atmospheric Dust has Masked Power of Greenhouse Gases to Warm Planet {{!}} Scripps Institution of Oceanography |url=https://scripps.ucsd.edu/news/increased-atmospheric-dust-has-masked-power-greenhouse-gases-warm-planet |access-date=2024-11-08 |website=scripps.ucsd.edu |language=en}}</ref> Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.<ref>{{harvnb|Wild|Gilgen|Roesch|Ohmura|2005}}; {{Harvnb|Storelvmo|Phillips|Lohmann|Leirvik|2016}}; {{harvnb|Samset|Sand|Smith|Bauer|2018}}.</ref><ref name="Quaas2022">{{Cite journal |last1=Quaas |first1=Johannes |last2=Jia |first2=Hailing |last3=Smith |first3=Chris |last4=Albright |first4=Anna Lea |last5=Aas |first5=Wenche |last6=Bellouin |first6=Nicolas |last7=Boucher |first7=Olivier |last8=Doutriaux-Boucher |first8=Marie |last9=Forster |first9=Piers M. |last10=Grosvenor |first10=Daniel |last11=Jenkins |first11=Stuart |last12=Klimont |first12=Zbigniew |last13=Loeb |first13=Norman G. |last14=Ma |first14=Xiaoyan |last15=Naik |first15=Vaishali |last16=Paulot |first16=Fabien |last17=Stier |first17=Philip |last18=Wild |first18=Martin |last19=Myhre |first19=Gunnar |last20=Schulz |first20=Michael |date=21 September 2022 |title=Robust evidence for reversal of the trend in aerosol effective climate forcing |url=https://acp.copernicus.org/articles/22/12221/2022/ |journal=Atmospheric Chemistry and Physics |volume=22 |issue=18 |pages=12221–12239 |language=en |doi=10.5194/acp-22-12221-2022 |s2cid=252446168 |hdl=20.500.11850/572791 |hdl-access=free |doi-access=free |bibcode=2022ACP....2212221Q }}</ref>


Aerosols also have indirect effects on the [[Earth's energy budget]]. Sulfate aerosols act as [[cloud condensation nuclei]] and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets.<ref>{{harvnb|Twomey|1977}}.</ref> They also reduce the [[Cloud physics#Collision-coalescence|growth of raindrops]], which makes clouds more reflective to incoming sunlight.<ref>{{harvnb|Albrecht|1989}}.</ref> Indirect effects of aerosols are the largest uncertainty in [[radiative forcing]].<ref name=USGCRP_2017_ch2/>
Aerosols also have indirect effects on the [[Earth's energy budget]]. Sulfate aerosols act as [[cloud condensation nuclei]] and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets.<ref>{{harvnb|Twomey|1977}}.</ref> They also reduce the [[Cloud physics#Collision-coalescence|growth of raindrops]], which makes clouds more reflective to incoming sunlight.<ref>{{harvnb|Albrecht|1989}}.</ref> Indirect effects of aerosols are the largest uncertainty in [[radiative forcing]].<ref name=USGCRP_2017_ch2/>


While aerosols typically limit global warming by reflecting sunlight, [[black carbon]] in [[soot]] that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise.<ref>{{harvnb|Ramanathan|Carmichael|2008}}; {{harvnb|RIVM|2016}}.</ref> Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2&nbsp;°C by 2050.<ref>{{harvnb|Sand|Berntsen|von Salzen|Flanner|2015}}</ref> The effect of decreasing sulfur content of fuel oil for ships since 2020<ref>{{Cite web|url=https://www.imo.org/en/MediaCentre/HotTopics/Pages/Sulphur-2020.aspx|title=IMO 2020 – cutting sulphur oxide emissions|website=www.imo.org}}</ref> is estimated to cause an additional 0.05&nbsp;°C increase in global mean temperature by 2050.<ref>{{harvnb|Carbon Brief, 3 July|2023}}</ref>
While aerosols typically limit global warming by reflecting sunlight, [[black carbon]] in [[soot]] that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise.<ref>{{harvnb|Ramanathan|Carmichael|2008}}; {{harvnb|RIVM|2016}}.</ref> Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2&nbsp;°C by 2050.<ref>{{harvnb|Sand|Berntsen|von Salzen|Flanner|2015}}</ref> The effect of decreasing sulfur content of fuel oil for ships since 2020<ref>{{Cite web|url=https://www.imo.org/en/MediaCentre/HotTopics/Pages/Sulphur-2020.aspx|title=IMO 2020 – cutting sulphur oxide emissions|website=imo.org}}</ref> is estimated to cause an additional 0.05&nbsp;°C increase in global mean temperature by 2050.<ref>{{harvnb|Carbon Brief, 3 July|2023}}</ref>


==== Solar and volcanic activity ====
==== Solar and volcanic activity ====
{{Further|Solar activity and climate}}
{{Further|Solar activity and climate}}
[[File:2017 Global warming attribution - based on NCA4 Fig 3.3 - single-panel version.svg|thumb|right|upright=1.35| The [[Fourth National Climate Assessment]] ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming.<ref>{{cite journal |title=Climate Science Special Report: Fourth National Climate Assessment, Volume I - Chapter 3: Detection and Attribution of Climate Change |url=https://science2017.globalchange.gov/chapter/3/ |website=science2017.globalchange.gov |publisher=U.S. Global Change Research Program (USGCRP) |archive-url=https://web.archive.org/web/20190923190450/https://science2017.globalchange.gov/chapter/3/ |archive-date=23 September 2019 |date=2017 |pages=1–470 |url-status=live}} Adapted directly from Fig. 3.3.</ref><ref>{{cite journal |title=Climate Science Special Report / Fourth National Climate Assessment (NCA4), Volume I /Executive Summary / Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report |url=https://science2017.globalchange.gov/chapter/executive-summary/ |website=globalchange.gov |publisher=U.S. Global Change Research Program |archive-url=https://web.archive.org/web/20190614150544/https://science2017.globalchange.gov/chapter/executive-summary/ |archive-date=14 June 2019 |date=23 November 2018 |doi=10.7930/J0DJ5CTG |url-status=live |last1=Wuebbles |first1=D.J. |last2=Fahey |first2=D.W. |last3=Hibbard |first3=K.A. |last4=Deangelo |first4=B. |last5=Doherty |first5=S. |last6=Hayhoe |first6=K. |last7=Horton |first7=R. |last8=Kossin |first8=J.P. |last9=Taylor |first9=P.C. |last10=Waple |first10=A.M. |last11=Yohe |first11=C.P. |pages=1–470 |doi-access=free}}</ref>]]
[[File:2017 Global warming attribution - based on NCA4 Fig 3.3 - single-panel version.svg|thumb|right|upright=1.35| The [[Fourth National Climate Assessment]] ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming.<ref>{{cite journal |title=Climate Science Special Report: Fourth National Climate Assessment, Volume I - Chapter 3: Detection and Attribution of Climate Change |url=https://science2017.globalchange.gov/chapter/3/ |website=science2017.globalchange.gov |publisher=U.S. Global Change Research Program (USGCRP) |archive-url=https://web.archive.org/web/20190923190450/https://science2017.globalchange.gov/chapter/3/ |archive-date=23 September 2019 |year=2017 |pages=1–470 |url-status=live}} Adapted directly from Fig. 3.3.</ref><ref>{{cite journal |last1=Wuebbles |first1=D. J. |last2=Fahey |first2=D. W. |last3=Hibbard |first3=K. A. |last4=Deangelo |first4=B. |last5=Doherty |first5=S. |last6=Hayhoe |first6=K. |last7=Horton |first7=R. |last8=Kossin |first8=J. P. |last9=Taylor |first9=P. C. |last10=Waple |first10=A. M. |last11=Yohe |first11=C. P. |date=23 November 2018 |title=Climate Science Special Report / Fourth National Climate Assessment (NCA4), Volume I /Executive Summary / Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report |url=https://science2017.globalchange.gov/chapter/executive-summary/ |url-status=live |publisher=U.S. Global Change Research Program |pages=1–470 |doi=10.7930/J0DJ5CTG |archive-url=https://web.archive.org/web/20190614150544/https://science2017.globalchange.gov/chapter/executive-summary/ |archive-date=14 June 2019 |doi-access=free |website=globalchange.gov}}</ref>]]
As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the [[climate system]].<ref name=USGCRP_2017_ch2>{{harvnb|USGCRP Chapter 2|2017|p=78}}.</ref> [[solar variation|Solar irradiance]] has been measured directly by [[satellite]]s,<ref>{{Harvnb|National Academies|2008|p=6}}</ref> and indirect measurements are available from the early 1600s onwards.<ref name=USGCRP_2017_ch2 /> Since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the [[troposphere]]).<ref>{{cite web|title=Is the Sun causing global warming?|website=Climate Change: Vital Signs of the Planet|url=https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming|access-date=10 May 2019|archive-url=https://web.archive.org/web/20190505160051/https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming/|archive-date=5 May 2019|url-status=live}}</ref> The upper atmosphere (the [[stratosphere]]) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.<ref name="USGCRP-2009">{{Harvnb|USGCRP|2009|p=20}}.</ref>
As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the [[climate system]].<ref name=USGCRP_2017_ch2>{{harvnb|USGCRP Chapter 2|2017|p=78}}.</ref> [[solar variation|Solar irradiance]] has been measured directly by [[satellite]]s,<ref>{{Harvnb|National Academies|2008|p=6}}</ref> and indirect measurements are available from the early 1600s onwards.<ref name=USGCRP_2017_ch2 /> Since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the [[troposphere]]).<ref>{{cite web|title=Is the Sun causing global warming?|website=Climate Change: Vital Signs of the Planet|url=https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming|access-date=10 May 2019|archive-url=https://web.archive.org/web/20190505160051/https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming/|archive-date=5 May 2019|url-status=live}}</ref> The upper atmosphere (the [[stratosphere]]) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.<ref name="USGCRP-2009">{{Harvnb|USGCRP|2009|p=20}}.</ref>
This is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.<ref>{{Harvnb|IPCC AR4 WG1 Ch9|2007|pp=702–703}}; {{harvnb|Randel|Shine|Austin|Barnett|2009}}.</ref>
This is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.<ref>{{Harvnb|IPCC AR4 WG1 Ch9|2007|pp=702–703}}; {{harvnb|Randel|Shine|Austin|Barnett|2009}}.</ref>
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Greater degrees of global warming increase the risk of passing through '[[Tipping points in the climate system|tipping points]]'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state.<ref>{{Harvnb|IPCC SR15 Ch3|2018|p=283}}.</ref><ref>{{Harvnb|Carbon Brief, 10 February|2020}}</ref> For instance, the [[Greenland ice sheet]] is already melting, but if global warming reaches levels between 1.7&nbsp;°C and 2.3&nbsp;°C, its melting will continue until it fully disappears. If the warming is later reduced to 1.5&nbsp;°C or less, it will still lose a lot more ice than if the warming was never allowed to reach the threshold in the first place.<ref name="Bochow2023">{{cite journal |last1=Bochow |first1=Nils |last2=Poltronieri |first2=Anna |last3=Robinson |first3=Alexander |last4=Montoya |first4=Marisa |last5=Rypdal |first5=Martin |last6=Boers |first6=Niklas |date=18 October 2023 |title=Overshooting the critical threshold for the Greenland ice sheet |journal=[[Nature (journal)|Nature]] |volume=622 |issue=7983 |pages=528–536 |bibcode=2023Natur.622..528B |doi=10.1038/s41586-023-06503-9 |pmc=10584691 |pmid=37853149}}</ref> While the ice sheets would melt over millennia, other tipping points would occur faster and give societies less time to respond. The collapse of major [[ocean current]]s like the [[Atlantic meridional overturning circulation]] (AMOC), and irreversible damage to key ecosystems like the [[Amazon rainforest]] and [[coral reefs]] can unfold in a matter of decades.<ref name="ArmstrongMcKay2022">{{Cite journal |last1=Armstrong McKay |first1=David I. |last2=Staal |first2=Arie |last3=Abrams |first3=Jesse F. |last4=Winkelmann |first4=Ricarda |last5=Sakschewski |first5=Boris |last6=Loriani |first6=Sina |last7=Fetzer |first7=Ingo |last8=Cornell |first8=Sarah E. |last9=Rockström |first9=Johan |last10=Lenton |first10=Timothy M. |date=9 September 2022 |title=Exceeding 1.5&nbsp;°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=[[Science (journal)|Science]] |volume=377 |issue=6611 |pages=eabn7950 |doi=10.1126/science.abn7950 |pmid=36074831 |hdl=10871/131584 |s2cid=252161375 |issn=0036-8075|hdl-access=free }}</ref>
Greater degrees of global warming increase the risk of passing through '[[Tipping points in the climate system|tipping points]]'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state.<ref>{{Harvnb|IPCC SR15 Ch3|2018|p=283}}.</ref><ref>{{Harvnb|Carbon Brief, 10 February|2020}}</ref> For instance, the [[Greenland ice sheet]] is already melting, but if global warming reaches levels between 1.7&nbsp;°C and 2.3&nbsp;°C, its melting will continue until it fully disappears. If the warming is later reduced to 1.5&nbsp;°C or less, it will still lose a lot more ice than if the warming was never allowed to reach the threshold in the first place.<ref name="Bochow2023">{{cite journal |last1=Bochow |first1=Nils |last2=Poltronieri |first2=Anna |last3=Robinson |first3=Alexander |last4=Montoya |first4=Marisa |last5=Rypdal |first5=Martin |last6=Boers |first6=Niklas |date=18 October 2023 |title=Overshooting the critical threshold for the Greenland ice sheet |journal=[[Nature (journal)|Nature]] |volume=622 |issue=7983 |pages=528–536 |bibcode=2023Natur.622..528B |doi=10.1038/s41586-023-06503-9 |pmc=10584691 |pmid=37853149}}</ref> While the ice sheets would melt over millennia, other tipping points would occur faster and give societies less time to respond. The collapse of major [[ocean current]]s like the [[Atlantic meridional overturning circulation]] (AMOC), and irreversible damage to key ecosystems like the [[Amazon rainforest]] and [[coral reefs]] can unfold in a matter of decades.<ref name="ArmstrongMcKay2022">{{Cite journal |last1=Armstrong McKay |first1=David I. |last2=Staal |first2=Arie |last3=Abrams |first3=Jesse F. |last4=Winkelmann |first4=Ricarda |last5=Sakschewski |first5=Boris |last6=Loriani |first6=Sina |last7=Fetzer |first7=Ingo |last8=Cornell |first8=Sarah E. |last9=Rockström |first9=Johan |last10=Lenton |first10=Timothy M. |date=9 September 2022 |title=Exceeding 1.5&nbsp;°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=[[Science (journal)|Science]] |volume=377 |issue=6611 |pages=eabn7950 |doi=10.1126/science.abn7950 |pmid=36074831 |hdl=10871/131584 |s2cid=252161375 |issn=0036-8075|hdl-access=free }}</ref>


The long-term [[effects of climate change on oceans]] include further ice melt, [[Ocean temperature#Increasing temperature due to climate change|ocean warming]], sea level rise, ocean acidification and ocean deoxygenation.<ref>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|p=21}}</ref> The timescale of long-term impacts are centuries to millennia due to {{CO2}}'s long atmospheric lifetime.<ref>{{Harvnb|IPCC AR5 WG1 Ch12|2013|pp=88–89|loc=FAQ 12.3}}</ref> The result is an estimated total sea level rise of {{convert|2.3|m/°C|ft/°F}} after 2000 years.<ref>{{harvnb|Smith|Schneider|Oppenheimer|Yohe|2009}}; {{harvnb|Levermann|Clark|Marzeion|Milne|2013}}</ref> Oceanic {{CO2}} uptake is slow enough that ocean acidification will also continue for hundreds to thousands of years.{{sfn|IPCC AR5 WG1 Ch12|2013|p=1112}} Deep oceans (below {{convert|2000|m|ft}}) are also already committed to losing over 10% of their dissolved oxygen by the warming which occurred to date.<ref>{{cite journal |last1=Oschlies |first1=Andreas |title=A committed fourfold increase in ocean oxygen loss |journal=Nature Communications |date=16 April 2021 |volume=12 |issue=1 |page=2307 |doi=10.1038/s41467-021-22584-4 |pmid=33863893 |pmc=8052459 |bibcode=2021NatCo..12.2307O }}</ref> Further, the [[West Antarctic ice sheet]] appears committed to practically irreversible melting, which would increase the sea levels by at least {{convert|3.3|m|ftin|abbr=on}} over approximately 2000 years.<ref name="ArmstrongMcKay2022" /><ref name="Lau2023">{{Cite journal |last1=Lau |first1=Sally C. Y. |last2=Wilson |first2=Nerida G. |last3=Golledge |first3=Nicholas R. |last4=Naish |first4=Tim R. |last5=Watts |first5=Phillip C. |last6=Silva |first6=Catarina N. S. |last7=Cooke |first7=Ira R. |last8=Allcock |first8=A. Louise |last9=Mark |first9=Felix C. |last10=Linse |first10=Katrin |date=21 December 2023 |title=Genomic evidence for West Antarctic Ice Sheet collapse during the Last Interglacial |url=https://epic.awi.de/id/eprint/58369/1/science.ade0664%281%29.pdf |journal=[[Science (journal)|Science]] |language=en |volume=382 |issue=6677 |pages=1384–1389 |bibcode=2023Sci...382.1384L |doi=10.1126/science.ade0664 |pmid=38127761 |s2cid=266436146}}</ref><ref name="Naughten2023">{{cite journal |last1=A. Naughten |first1=Kaitlin |last2=R. Holland |first2=Paul |last3=De Rydt |first3=Jan |date=23 October 2023 |title=Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century |journal=[[Nature Climate Change]] |volume=13 |issue=11 |pages=1222–1228 |bibcode=2023NatCC..13.1222N |doi=10.1038/s41558-023-01818-x |s2cid=264476246 |doi-access=free}}</ref>
The long-term [[effects of climate change on oceans]] include further ice melt, [[Ocean temperature#Increasing temperature due to climate change|ocean warming]], sea level rise, ocean acidification and ocean deoxygenation.<ref>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|p=21}}</ref> The timescale of long-term impacts are centuries to millennia due to {{CO2}}'s long atmospheric lifetime.<ref>{{Harvnb|IPCC AR5 WG1 Ch12|2013|pp=88–89|loc=FAQ 12.3}}</ref> The result is an estimated total sea level rise of {{convert|2.3|m/°C|ft/°F}} after 2000 years.<ref>{{harvnb|Smith|Schneider|Oppenheimer|Yohe|2009}}; {{harvnb|Levermann|Clark|Marzeion|Milne|2013}}</ref> Oceanic {{CO2}} uptake is slow enough that ocean acidification will also continue for hundreds to thousands of years.{{sfn|IPCC AR5 WG1 Ch12|2013|p=1112}} Deep oceans (below {{convert|2000|m|ft}}) are also already committed to losing over 10% of their dissolved oxygen by the warming which occurred to date.<ref>{{cite journal |last1=Oschlies |first1=Andreas |title=A committed fourfold increase in ocean oxygen loss |journal=Nature Communications |date=16 April 2021 |volume=12 |issue=1 |page=2307 |doi=10.1038/s41467-021-22584-4 |pmid=33863893 |pmc=8052459 |bibcode=2021NatCo..12.2307O }}</ref> Further, the [[West Antarctic ice sheet]] appears committed to practically irreversible melting, which would increase the sea levels by at least {{convert|3.3|m|ftin|abbr=on}} over approximately 2000 years.<ref name="ArmstrongMcKay2022" /><ref name="Lau2023">{{Cite journal |last1=Lau |first1=Sally C. Y. |last2=Wilson |first2=Nerida G. |last3=Golledge |first3=Nicholas R. |last4=Naish |first4=Tim R. |last5=Watts |first5=Phillip C. |last6=Silva |first6=Catarina N. S. |last7=Cooke |first7=Ira R. |last8=Allcock |first8=A. Louise |last9=Mark |first9=Felix C. |last10=Linse |first10=Katrin |date=21 December 2023 |title=Genomic evidence for West Antarctic Ice Sheet collapse during the Last Interglacial |url=https://epic.awi.de/id/eprint/58369/1/science.ade0664%281%29.pdf |journal=[[Science (journal)|Science]] |volume=382 |issue=6677 |pages=1384–1389 |bibcode=2023Sci...382.1384L |doi=10.1126/science.ade0664 |pmid=38127761 |s2cid=266436146}}</ref><ref name="Naughten2023">{{cite journal |last1=Naughten |first1=Kaitlin A. |last2=Holland |first2=Paul R. |last3=De Rydt |first3=Jan |date=23 October 2023 |title=Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century |journal=[[Nature Climate Change]] |volume=13 |issue=11 |pages=1222–1228 |bibcode=2023NatCC..13.1222N |doi=10.1038/s41558-023-01818-x |s2cid=264476246 |doi-access=free}}</ref>


===Nature and wildlife===
===Nature and wildlife===
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[[File:20211109 Frequency of extreme weather for different degrees of global warming - bar chart IPCC AR6 WG1 SPM.svg|thumb|upright=1.35 |Extreme weather will be progressively more common as the Earth warms.<ref name=IPCC6AR_ExtremeEvents>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|loc=Fig. SPM.6
[[File:20211109 Frequency of extreme weather for different degrees of global warming - bar chart IPCC AR6 WG1 SPM.svg|thumb|upright=1.35 |Extreme weather will be progressively more common as the Earth warms.<ref name=IPCC6AR_ExtremeEvents>{{harvnb|IPCC AR6 WG1 Summary for Policymakers|2021|loc=Fig. SPM.6
|page=SPM-23}}</ref>]]
|page=SPM-23}}</ref>]]
The effects of climate change are impacting humans everywhere in the world.<ref>{{cite journal |last1=Lenton |first1=Timothy M. |last2=Xu |first2=Chi |last3=Abrams |first3=Jesse F. |last4=Ghadiali |first4=Ashish |last5=Loriani |first5=Sina |last6=Sakschewski |first6=Boris |last7=Zimm |first7=Caroline |last8=Ebi |first8=Kristie L. |last9=Dunn |first9=Robert R. |last10=Svenning |first10=Jens-Christian |last11=Scheffer |first11=Marten |title=Quantifying the human cost of global warming |journal=[[Nature Sustainability]] |date=2023 |volume=6 |issue=10 |pages=1237–1247 |doi=10.1038/s41893-023-01132-6 |doi-access=free|bibcode=2023NatSu...6.1237L |hdl=10871/132650 |hdl-access=free }}</ref> Impacts can be observed on all continents and ocean regions,<ref>{{Harvnb|IPCC AR5 WG2 Ch18|2014|pp=983, 1008}}</ref> with low-latitude, [[Developing country|less developed areas]] facing the greatest risk.<ref>{{Harvnb|IPCC AR5 WG2 Ch19|2014|p=1077}}.</ref> Continued warming has potentially "severe, pervasive and irreversible impacts" for people and ecosystems.<ref>{{harvnb|IPCC AR5 SYR Summary for Policymakers|2014|loc=SPM 2|p=8}}</ref> The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries.<ref>{{harvnb|IPCC AR5 SYR Summary for Policymakers|2014|loc=SPM 2.3|p=13}}</ref>
The effects of climate change are impacting humans everywhere in the world.<ref>{{cite journal |last1=Lenton |first1=Timothy M. |last2=Xu |first2=Chi |last3=Abrams |first3=Jesse F. |last4=Ghadiali |first4=Ashish |last5=Loriani |first5=Sina |last6=Sakschewski |first6=Boris |last7=Zimm |first7=Caroline |last8=Ebi |first8=Kristie L. |last9=Dunn |first9=Robert R. |last10=Svenning |first10=Jens-Christian |last11=Scheffer |first11=Marten |title=Quantifying the human cost of global warming |journal=[[Nature Sustainability]] |year=2023 |volume=6 |issue=10 |pages=1237–1247 |doi=10.1038/s41893-023-01132-6 |doi-access=free|bibcode=2023NatSu...6.1237L |hdl=10871/132650 |hdl-access=free }}</ref> Impacts can be observed on all continents and ocean regions,<ref>{{Harvnb|IPCC AR5 WG2 Ch18|2014|pp=983, 1008}}</ref> with low-latitude, [[Developing country|less developed areas]] facing the greatest risk.<ref>{{Harvnb|IPCC AR5 WG2 Ch19|2014|p=1077}}.</ref> Continued warming has potentially "severe, pervasive and irreversible impacts" for people and ecosystems.<ref>{{harvnb|IPCC AR5 SYR Summary for Policymakers|2014|loc=SPM 2|p=8}}</ref> The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries.<ref>{{harvnb|IPCC AR5 SYR Summary for Policymakers|2014|loc=SPM 2.3|p=13}}</ref>


==== Health and food ====
==== Health and food ====
{{Main|Effects of climate change on agriculture#Global food security and undernutrition|Effects of climate change on human health}}
{{Main|Effects of climate change on agriculture#Global food security and undernutrition|Effects of climate change on human health}}
The [[World Health Organization]] calls climate change one of the biggest threats to global health in the 21st century.<ref name=WHO_Nov_2023/> Scientists have warned about the irreversible harms it poses.<ref name=Romanello_et_al_2023>{{harvnb|Romanello|2023}}</ref> [[Extreme weather]] events affect public health, and [[Food security|food]] and [[water security]].<ref name=nca2018_ch14>{{harvnb|Ebi et al.|2018}}</ref><ref name=Romanello_et_al_2022>{{harvnb|Romanello|2022}}</ref><ref name=IPCC_AR6_WG2_p9>{{harvnb|IPCC AR6 WG2 SPM|2022|p=9}}</ref> [[Effects of climate change#Heat waves and temperature extremes|Temperature extremes]] lead to increased illness and death.<ref name=nca2018_ch14/><ref name=Romanello_et_al_2022/> Climate change increases the intensity and frequency of extreme weather events.<ref name=Romanello_et_al_2022/><ref name=IPCC_AR6_WG2_p9/> It can affect transmission of [[infectious diseases]], such as [[dengue fever]] and [[malaria]].<ref name=Romanello_et_al_2023/><ref name=nca2018_ch14/> According to the [[World Economic Forum]], 14.5 million more deaths are expected due to climate change by 2050.<ref>{{harvnb|World Economic Forum|2024|p=4}}</ref> 30% of the global population currently live in areas where extreme heat and humidity are already associated with excess deaths.<ref name=Carbon_Brief_2017>{{harvnb|Carbon Brief, 19 June|2017}}</ref><ref>{{harvnb|Mora et al.|2017}}</ref> By 2100, 50% to 75% of the global population would live in such areas.<ref name=Carbon_Brief_2017/><ref>{{harvnb|IPCC AR6 WG2 Ch6|2022|p=988}}</ref>
The [[World Health Organization]] calls climate change one of the biggest threats to global health in the 21st century.<ref name=WHO_Nov_2023/> Scientists have warned about the irreversible harms it poses.<ref name=Romanello_et_al_2023>{{harvnb|Romanello|2023}}</ref> [[Extreme weather]] events affect public health, and [[Food security|food]] and [[water security]].<ref name=nca2018_ch14>{{harvnb|Ebi et al.|2018}}</ref><ref name=Romanello_et_al_2022>{{harvnb|Romanello|2022}}</ref><ref name=IPCC_AR6_WG2_p9>{{harvnb|IPCC AR6 WG2 SPM|2022|p=9}}</ref> [[Effects of climate change#Heat waves and temperature extremes|Temperature extremes]] lead to increased illness and death.<ref name=nca2018_ch14/><ref name=Romanello_et_al_2022/> Climate change increases the intensity and frequency of extreme weather events.<ref name=Romanello_et_al_2022/><ref name=IPCC_AR6_WG2_p9/> It can affect transmission of [[infectious diseases]], such as [[dengue fever]] and [[malaria]].<ref name=Romanello_et_al_2023/><ref name=nca2018_ch14/> According to the [[World Economic Forum]], 14.5&nbsp;million more deaths are expected due to climate change by 2050.<ref>{{harvnb|World Economic Forum|2024|p=4}}</ref> 30% of the global population currently live in areas where extreme heat and humidity are already associated with excess deaths.<ref name=Carbon_Brief_2017>{{harvnb|Carbon Brief, 19 June|2017}}</ref><ref>{{harvnb|Mora et al.|2017}}</ref> By 2100, 50% to 75% of the global population would live in such areas.<ref name=Carbon_Brief_2017/><ref>{{harvnb|IPCC AR6 WG2 Ch6|2022|p=988}}</ref>


While total [[crop yield]]s have been increasing in the past 50 years due to agricultural improvements, [[Effects of climate change on agriculture|climate change has already decreased the rate of yield growth]].<ref name=IPCC_AR6_WG2_p9/> [[Climate change and fisheries|Fisheries have been negatively affected]] in multiple regions.<ref name=IPCC_AR6_WG2_p9/> While [[agricultural productivity]] has been positively affected in some high [[latitude]] areas, mid- and low-latitude areas have been negatively affected.<ref name=IPCC_AR6_WG2_p9/> According to the World Economic Forum, an increase in [[drought]] in certain regions could cause 3.2 million deaths from [[malnutrition]] by 2050 and [[Stunted growth|stunting]] in children.<ref>{{harvnb|World Economic Forum|2024|p=24}}</ref> With 2&nbsp;°C warming, global [[livestock]] headcounts could decline by 7–10% by 2050, as less animal feed will be available.<ref>{{harvnb|IPCC AR6 WG2 Ch5|2022|p=748}}</ref> If the emissions continue to increase for the rest of century, then over 9 million climate-related deaths would occur annually by 2100.<ref>{{harvnb|IPCC AR6 WG2 Technical Summary|2022|p=63}}</ref>
While total [[crop yield]]s have been increasing in the past 50 years due to agricultural improvements, [[Effects of climate change on agriculture|climate change has already decreased the rate of yield growth]].<ref name=IPCC_AR6_WG2_p9/> [[Climate change and fisheries|Fisheries have been negatively affected]] in multiple regions.<ref name=IPCC_AR6_WG2_p9/> While [[agricultural productivity]] has been positively affected in some high [[latitude]] areas, mid- and low-latitude areas have been negatively affected.<ref name=IPCC_AR6_WG2_p9/> According to the World Economic Forum, an increase in [[drought]] in certain regions could cause 3.2&nbsp;million deaths from [[malnutrition]] by 2050 and [[Stunted growth|stunting]] in children.<ref>{{harvnb|World Economic Forum|2024|p=24}}</ref> With 2&nbsp;°C warming, global [[livestock]] headcounts could decline by 7–10% by 2050, as less animal feed will be available.<ref>{{harvnb|IPCC AR6 WG2 Ch5|2022|p=748}}</ref> If the emissions continue to increase for the rest of century, then over 9 million climate-related deaths would occur annually by 2100.<ref>{{harvnb|IPCC AR6 WG2 Technical Summary|2022|p=63}}</ref>


==== Livelihoods and inequality ====
==== Livelihoods and inequality ====
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{{main|Climate change mitigation}}
{{main|Climate change mitigation}}
[[File:Greenhouse gas emission scenarios 01.svg|thumb|upright=1.35|right|Global greenhouse gas emission scenarios, based on policies and pledges as of November 2021]]
[[File:Greenhouse gas emission scenarios 01.svg|thumb|upright=1.35|right|Global greenhouse gas emission scenarios, based on policies and pledges as of November 2021]]
Climate change can be mitigated by reducing the rate at which greenhouse gases are emitted into the atmosphere, and by increasing the rate at which carbon dioxide is removed from the atmosphere.<ref>{{harvnb|IPCC AR5 SYR Glossary|2014|p=125}}.</ref> In order to limit global warming to less than 1.5&nbsp;°C global greenhouse gas emissions needs to be [[Carbon neutrality|net-zero]] by 2050, or by 2070 with a 2&nbsp;°C target.<ref name="IPCC-2018 p12">{{harvnb|IPCC SR15 Summary for Policymakers|2018|p=12}}</ref> This requires far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry.<ref>{{harvnb|IPCC SR15 Summary for Policymakers|2018|p=15}}</ref>
Climate change can be mitigated by reducing the rate at which greenhouse gases are emitted into the atmosphere, and by increasing the rate at which carbon dioxide is removed from the atmosphere.<ref>{{harvnb|IPCC AR5 SYR Glossary|2014|p=125}}.</ref> To limit global warming to less than 1.5&nbsp;°C global greenhouse gas emissions needs to be [[Carbon neutrality|net-zero]] by 2050, or by 2070 with a 2&nbsp;°C target.<ref name="IPCC-2018 p12">{{harvnb|IPCC SR15 Summary for Policymakers|2018|p=12}}</ref> This requires far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry.<ref>{{harvnb|IPCC SR15 Summary for Policymakers|2018|p=15}}</ref>


The [[United Nations Environment Programme]] estimates that countries need to triple their [[Nationally determined contribution|pledges under the Paris Agreement]] within the next decade to limit global warming to 2&nbsp;°C. An even greater level of reduction is required to meet the 1.5&nbsp;°C goal.<ref>{{harvnb|United Nations Environment Programme|2019|p=XX}}</ref> With pledges made under the Paris Agreement as of 2024, there would be a 66% chance that global warming is kept under 2.8&nbsp;°C by the end of the century (range: 1.9–3.7&nbsp;°C, depending on exact implementation and technological progress). When only considering current policies, this raises to 3.1&nbsp;°C.{{sfn|United Nations Environment Programme|2024|pp=33, 34}} Globally, limiting warming to 2&nbsp;°C may result in higher economic benefits than economic costs.<ref>{{harvnb|IPCC AR6 WG3 Ch3|2022|p=300}}: "The global benefits of pathways limiting warming to 2&nbsp;°C (>67%) outweigh global mitigation costs over the 21st century, if aggregated economic impacts of climate change are at the moderate to high end of the assessed range, and a weight consistent with economic theory is given to economic impacts over the long term. This holds true even without accounting for benefits in other sustainable development dimensions or nonmarket damages from climate change (medium confidence)."</ref>
The [[United Nations Environment Programme]] estimates that countries need to triple their [[Nationally determined contribution|pledges under the Paris Agreement]] within the next decade to limit global warming to 2&nbsp;°C. An even greater level of reduction is required to meet the 1.5&nbsp;°C goal.<ref>{{harvnb|United Nations Environment Programme|2019|p=XX}}</ref> With pledges made under the Paris Agreement as of 2024, there would be a 66% chance that global warming is kept under 2.8&nbsp;°C by the end of the century (range: 1.9–3.7&nbsp;°C, depending on exact implementation and technological progress). When only considering current policies, this raises to 3.1&nbsp;°C.{{sfn|United Nations Environment Programme|2024|pp=33, 34}} Globally, limiting warming to 2&nbsp;°C may result in higher economic benefits than economic costs.<ref>{{harvnb|IPCC AR6 WG3 Ch3|2022|p=300}}: "The global benefits of pathways limiting warming to 2&nbsp;°C (>67%) outweigh global mitigation costs over the 21st century, if aggregated economic impacts of climate change are at the moderate to high end of the assessed range, and a weight consistent with economic theory is given to economic impacts over the long term. This holds true even without accounting for benefits in other sustainable development dimensions or nonmarket damages from climate change (medium confidence)."</ref>
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While [[Photovoltaic system|solar panels]] and onshore wind are now among the cheapest forms of adding new power generation capacity in many locations,<ref>{{harvnb|Our World in Data-Why did renewables become so cheap so fast?}}; {{harvnb| IEA – Projected Costs of Generating Electricity 2020}}</ref> green energy policies are needed to achieve a rapid transition from fossil fuels to renewables.<ref>{{cite web |url=https://www.ipcc.ch/2022/04/04/ipcc-ar6-wgiii-pressrelease/ |title=IPCC Working Group III report: Mitigation of Climate Change |date=4 April 2022 |access-date=19 January 2024 |publisher=Intergovernmental Panel on Climate Change}}</ref> To achieve carbon neutrality by 2050, renewable energy would become the dominant form of electricity generation, rising to 85% or more by 2050 in some scenarios. Investment in coal would be eliminated and coal use nearly phased out by 2050.<ref>{{harvnb|IPCC SR15 Ch2|2018|loc=Figure 2.15|p=131}}</ref><ref>{{harvnb|Teske|2019|pp=409–410}}.</ref>
While [[Photovoltaic system|solar panels]] and onshore wind are now among the cheapest forms of adding new power generation capacity in many locations,<ref>{{harvnb|Our World in Data-Why did renewables become so cheap so fast?}}; {{harvnb| IEA – Projected Costs of Generating Electricity 2020}}</ref> green energy policies are needed to achieve a rapid transition from fossil fuels to renewables.<ref>{{cite web |url=https://www.ipcc.ch/2022/04/04/ipcc-ar6-wgiii-pressrelease/ |title=IPCC Working Group III report: Mitigation of Climate Change |date=4 April 2022 |access-date=19 January 2024 |publisher=Intergovernmental Panel on Climate Change}}</ref> To achieve carbon neutrality by 2050, renewable energy would become the dominant form of electricity generation, rising to 85% or more by 2050 in some scenarios. Investment in coal would be eliminated and coal use nearly phased out by 2050.<ref>{{harvnb|IPCC SR15 Ch2|2018|loc=Figure 2.15|p=131}}</ref><ref>{{harvnb|Teske|2019|pp=409–410}}.</ref>


Electricity generated from renewable sources would also need to become the main energy source for heating and transport.<ref>{{harvnb|United Nations Environment Programme|2019|loc=Table ES.3|p=XXIII}}; {{harvnb|Teske, ed.|2019|p=xxvii, Fig.5}}.</ref> Transport can switch away from [[internal combustion engine]] vehicles and towards [[electric vehicle]]s, public transit, and [[Active mobility|active transport]] (cycling and walking).<ref name="IPCC-2018 p142">{{harvnb|IPCC SR15 Ch2|2018|pp=142–144}}; {{harvnb|United Nations Environment Programme|2019|loc=Table ES.3 & p. 49}}</ref><ref>{{Cite web |date=2016 |title=Transport emissions |url=https://ec.europa.eu/clima/eu-action/transport-emissions_en |access-date=2 January 2022 |website=Climate action |publisher=[[European Commission]] |archive-url=https://web.archive.org/web/20211010225533/https://ec.europa.eu/clima/eu-action/transport-emissions_en |archive-date=10 October 2021 |url-status=live}}</ref> For shipping and flying, low-carbon fuels would reduce emissions.<ref name="IPCC-2018 p142" /> Heating could be increasingly decarbonized with technologies like [[heat pump]]s.<ref>{{harvnb|IPCC AR5 WG3 Ch9|2014|p=697}}; {{harvnb|NREL|2017|pp=vi, 12}}</ref>
Electricity generated from renewable sources would also need to become the main energy source for heating and transport.<ref>{{harvnb|United Nations Environment Programme|2019|loc=Table ES.3|p=XXIII}}; {{harvnb|Teske, ed.|2019|p=xxvii, Fig.5}}.</ref> Transport can switch away from [[internal combustion engine]] vehicles and towards [[electric vehicle]]s, public transit, and [[Active mobility|active transport]] (cycling and walking).<ref name="IPCC-2018 p142">{{harvnb|IPCC SR15 Ch2|2018|pp=142–144}}; {{harvnb|United Nations Environment Programme|2019|loc=Table ES.3 & p. 49}}</ref><ref>{{Cite web |year=2016 |title=Transport emissions |url=https://ec.europa.eu/clima/eu-action/transport-emissions_en |access-date=2 January 2022 |website=Climate action |publisher=[[European Commission]] |archive-url=https://web.archive.org/web/20211010225533/https://ec.europa.eu/clima/eu-action/transport-emissions_en |archive-date=10 October 2021 |url-status=live}}</ref> For shipping and flying, low-carbon fuels would reduce emissions.<ref name="IPCC-2018 p142" /> Heating could be increasingly decarbonized with technologies like [[heat pump]]s.<ref>{{harvnb|IPCC AR5 WG3 Ch9|2014|p=697}}; {{harvnb|NREL|2017|pp=vi, 12}}</ref>


There are obstacles to the continued rapid growth of clean energy, including renewables.<ref>{{harvnb|Berrill|Arvesen|Scholz|Gils|2016}}.</ref> Wind and solar produce energy [[Variable renewable energy|intermittently and with seasonal variability]]. Traditionally, [[Pumped-storage hydroelectricity|hydro dams with reservoirs]] and fossil fuel power plants have been used when variable energy production is low. Going forward, [[Battery storage power station|battery storage]] can be expanded, [[Demand response|energy demand and supply]] can be matched, and long-distance [[Electric power transmission|transmission]] can smooth variability of renewable outputs.<ref name="United Nations Environment Programme 2019 46">{{harvnb|United Nations Environment Programme|2019|p=46}}; {{harvnb|Vox, 20 September|2019}}; {{cite journal |title=The Role of Firm Low-Carbon Electricity Resources in Deep Decarbonization of Power Generation |year=2018 |last1=Sepulveda |first1=Nestor A. |last2=Jenkins |first2=Jesse D. |last3=De Sisternes |first3=Fernando J. |last4=Lester |first4=Richard K. |journal=[[Joule (journal)|Joule]] |volume=2 |issue=11 |pages=2403–2420 |doi=10.1016/j.joule.2018.08.006 |doi-access=free|bibcode=2018Joule...2.2403S }}</ref> Bioenergy is often not carbon-neutral and may have negative consequences for food security.<ref>{{harvnb|IPCC SR15 Ch4|2018|pp=324–325}}.</ref> The growth of nuclear power is constrained by controversy around [[radioactive waste]], [[nuclear proliferation|nuclear weapon proliferation]], and [[Nuclear accident|accidents]].<ref>{{Citec|last1=Gill |first1=Matthew |last2=Livens |first2=Francis |last3=Peakman |first3=Aiden |in=Letcher |year=2020 |pages=147–149 |chapter=Nuclear Fission}}</ref><ref>{{Cite journal |last1=Horvath |first1=Akos |last2=Rachlew |first2=Elisabeth |date=January 2016 |title=Nuclear power in the 21st century: Challenges and possibilities |journal=[[Ambio]] |volume=45 |issue=Suppl 1 |pages=S38–49 |doi=10.1007/s13280-015-0732-y |issn=1654-7209 |pmc=4678124 |pmid=26667059|bibcode=2016Ambio..45S..38H }}</ref> Hydropower growth is limited by the fact that the best sites have been developed, and new projects are confronting increased social and environmental concerns.<ref>{{cite web |title=Hydropower |url=https://www.iea.org/reports/hydropower |website=iea.org |publisher=[[International Energy Agency]] |access-date=12 October 2020 |quote=Hydropower generation is estimated to have increased by over 2% in 2019 owing to continued recovery from drought in Latin America as well as strong capacity expansion and good water availability in China (...) capacity expansion has been losing speed. This downward trend is expected to continue, due mainly to less large-project development in China and Brazil, where concerns over social and environmental impacts have restricted projects.}}</ref>
There are obstacles to the continued rapid growth of clean energy, including renewables.<ref>{{harvnb|Berrill|Arvesen|Scholz|Gils|2016}}.</ref> Wind and solar produce energy [[Variable renewable energy|intermittently and with seasonal variability]]. Traditionally, [[Pumped-storage hydroelectricity|hydro dams with reservoirs]] and fossil fuel power plants have been used when variable energy production is low. Going forward, [[Battery storage power station|battery storage]] can be expanded, [[Demand response|energy demand and supply]] can be matched, and long-distance [[Electric power transmission|transmission]] can smooth variability of renewable outputs.<ref name="United Nations Environment Programme 2019 46">{{harvnb|United Nations Environment Programme|2019|p=46}}; {{harvnb|Vox, 20 September|2019}}; {{cite journal |title=The Role of Firm Low-Carbon Electricity Resources in Deep Decarbonization of Power Generation |year=2018 |last1=Sepulveda |first1=Nestor A. |last2=Jenkins |first2=Jesse D. |last3=De Sisternes |first3=Fernando J. |last4=Lester |first4=Richard K. |journal=[[Joule (journal)|Joule]] |volume=2 |issue=11 |pages=2403–2420 |doi=10.1016/j.joule.2018.08.006 |doi-access=free|bibcode=2018Joule...2.2403S }}</ref> Bioenergy is often not carbon-neutral and may have negative consequences for food security.<ref>{{harvnb|IPCC SR15 Ch4|2018|pp=324–325}}.</ref> The growth of nuclear power is constrained by controversy around [[radioactive waste]], [[nuclear proliferation|nuclear weapon proliferation]], and [[Nuclear accident|accidents]].<ref>{{Citec|last1=Gill |first1=Matthew |last2=Livens |first2=Francis |last3=Peakman |first3=Aiden |in=Letcher |year=2020 |pages=147–149 |chapter=Nuclear Fission}}</ref><ref>{{Cite journal |last1=Horvath |first1=Akos |last2=Rachlew |first2=Elisabeth |date=January 2016 |title=Nuclear power in the 21st century: Challenges and possibilities |journal=[[Ambio]] |volume=45 |issue=Suppl 1 |pages=S38–49 |doi=10.1007/s13280-015-0732-y |issn=1654-7209 |pmc=4678124 |pmid=26667059|bibcode=2016Ambio..45S..38H }}</ref> Hydropower growth is limited by the fact that the best sites have been developed, and new projects are confronting increased social and environmental concerns.<ref>{{cite web |title=Hydropower |url=https://www.iea.org/reports/hydropower |website=iea.org |publisher=[[International Energy Agency]] |access-date=12 October 2020 |quote=Hydropower generation is estimated to have increased by over 2% in 2019 owing to continued recovery from drought in Latin America as well as strong capacity expansion and good water availability in China (...) capacity expansion has been losing speed. This downward trend is expected to continue, due mainly to less large-project development in China and Brazil, where concerns over social and environmental impacts have restricted projects.}}</ref>
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=== Agriculture and industry ===
=== Agriculture and industry ===
{{See also|Sustainable agriculture|Green industrial policy}}
{{See also|Sustainable agriculture|Green industrial policy}}
[[File:Greenhouse Gas Emissions by Economic Sector.svg|thumb|upright=1.35|Taking into account direct and indirect emissions, industry is the sector with the highest share of global emissions. Data as of 2019 from the IPCC.]] Agriculture and forestry face a triple challenge of limiting greenhouse gas emissions, preventing the further conversion of forests to agricultural land, and meeting increases in world food demand.<ref>{{harvnb|World Resources Institute, December|2019|p=1}}</ref> A set of actions could reduce agriculture and forestry-based emissions by two thirds from 2010 levels. These include reducing growth in demand for food and other agricultural products, increasing land productivity, protecting and restoring forests, and reducing greenhouse gas emissions from agricultural production.<ref>{{harvnb|World Resources Institute, December|2019|pp=1, 3}}</ref>
[[File:Greenhouse Gas Emissions by Economic Sector.svg|thumb|upright=1.35|Taking into account direct and indirect emissions, industry is the sector with the highest share of global emissions. Data as of 2019 from the IPCC.]] Agriculture and forestry face a triple challenge of limiting greenhouse gas emissions, preventing the further conversion of forests to agricultural land, and meeting increases in world food demand.<ref>{{harvnb|World Resources Institute, December|2019|p=1}}</ref> A set of actions could reduce agriculture and forestry-based emissions by two-thirds from 2010 levels. These include reducing growth in demand for food and other agricultural products, increasing land productivity, protecting and restoring forests, and reducing greenhouse gas emissions from agricultural production.<ref>{{harvnb|World Resources Institute, December|2019|pp=1, 3}}</ref>


On the demand side, a key component of reducing emissions is shifting people towards [[plant-based diets]].<ref>{{Harvnb|IPCC SRCCL|2019|p=22|loc=B.6.2}}</ref> Eliminating the production of livestock for [[Environmental impact of meat production|meat and dairy]] would eliminate about 3/4ths of all emissions from agriculture and other land use.<ref>{{Harvnb|IPCC SRCCL Ch5|2019|pp=487,488|loc=FIGURE 5.12}} Humans on a vegan exclusive diet would save about 7.9 Gt{{CO2}} equivalent per year by 2050 {{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=51}} Agriculture, Forestry and Other Land Use used an average of 12 Gt{{CO2}} per year between 2007 and 2016 (23% of total anthropogenic emissions).</ref> Livestock also occupy 37% of ice-free land area on Earth and consume feed from the 12% of land area used for crops, driving deforestation and land degradation.<ref>{{Harvnb|IPCC SRCCL Ch5|2019|pp=82, 162|loc=FIGURE 1.1}}</ref>
On the demand side, a key component of reducing emissions is shifting people towards [[plant-based diets]].<ref>{{Harvnb|IPCC SRCCL|2019|p=22|loc=B.6.2}}</ref> Eliminating the production of livestock for [[Environmental impact of meat production|meat and dairy]] would eliminate about 3/4ths of all emissions from agriculture and other land use.<ref>{{Harvnb|IPCC SRCCL Ch5|2019|pp=487,488|loc=FIGURE 5.12}} Humans on a vegan exclusive diet would save about 7.9 Gt{{CO2}} equivalent per year by 2050 {{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=51}} Agriculture, Forestry and Other Land Use used an average of 12 Gt{{CO2}} per year between 2007 and 2016 (23% of total anthropogenic emissions).</ref> Livestock also occupy 37% of ice-free land area on Earth and consume feed from the 12% of land area used for crops, driving deforestation and land degradation.<ref>{{Harvnb|IPCC SRCCL Ch5|2019|pp=82, 162|loc=FIGURE 1.1}}</ref>
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== Adaptation ==
== Adaptation ==
{{main|Climate change adaptation}}
{{main|Climate change adaptation}}
Adaptation is "the process of adjustment to current or expected changes in climate and its effects".<ref name="IPCC-2022">IPCC, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_SummaryForPolicymakers.pdf Summary for Policymakers] [H.-O. Pörtner, D.C. Roberts, E.S. Poloczanska, K. Mintenbeck, M. Tignor, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem (eds.)]. In: [https://www.ipcc.ch/report/sixth-assessment-report-working-group-ii/ Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge and New York, pp. 3–33, {{doi|10.1017/9781009325844.001}}.</ref>{{rp|5}} Without additional mitigation, adaptation cannot avert the risk of "severe, widespread and irreversible" impacts.{{sfn|IPCC AR5 SYR|2014|p=17}} More severe climate change requires more transformative adaptation, which can be prohibitively expensive.{{sfn|IPCC SR15 Ch4|2018|pp=396–397}} The [[Adaptive capacity|capacity and potential for humans to adapt]] is unevenly distributed across different regions and populations, and developing countries generally have less.<ref>{{Harvnb|IPCC AR4 WG2 Ch19|2007|p=796}}.</ref> The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic [[sanitation]] and electricity, but progress is slow. Many countries have implemented adaptation policies. However, there is a considerable gap between necessary and available finance.{{sfn|UNEP|2018|pp=xii–xiii}}
Adaptation is "the process of adjustment to current or expected changes in climate and its effects".<ref name="IPCC-2022">IPCC, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_SummaryForPolicymakers.pdf Summary for Policymakers] [H.-O. Pörtner, D. C. Roberts, E. S. Poloczanska, K. Mintenbeck, M. Tignor, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem (eds.)]. In: [https://www.ipcc.ch/report/sixth-assessment-report-working-group-ii/ Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [H.-O. Pörtner, D. C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge and New York, pp. 3–33, {{doi|10.1017/9781009325844.001}}.</ref>{{rp|5}} Without additional mitigation, adaptation cannot avert the risk of "severe, widespread and irreversible" impacts.{{sfn|IPCC AR5 SYR|2014|p=17}} More severe climate change requires more transformative adaptation, which can be prohibitively expensive.{{sfn|IPCC SR15 Ch4|2018|pp=396–397}} The [[Adaptive capacity|capacity and potential for humans to adapt]] is unevenly distributed across different regions and populations, and developing countries generally have less.<ref>{{Harvnb|IPCC AR4 WG2 Ch19|2007|p=796}}.</ref> The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic [[sanitation]] and electricity, but progress is slow. Many countries have implemented adaptation policies. However, there is a considerable gap between necessary and available finance.{{sfn|UNEP|2018|pp=xii–xiii}}


Adaptation to sea level rise consists of avoiding at-risk areas, learning to live with increased flooding, and building [[flood control]]s. If that fails, [[managed retreat]] may be needed.<ref>{{Cite journal |last1=Stephens |first1=Scott A. |last2=Bell |first2=Robert G. |last3=Lawrence |first3=Judy |date=2018 |title=Developing signals to trigger adaptation to sea-level rise |journal=[[Environmental Research Letters]] |volume=13 |issue=10 |at=104004 |doi=10.1088/1748-9326/aadf96 |bibcode=2018ERL....13j4004S |issn=1748-9326 |doi-access=free}}</ref> There are economic barriers for tackling dangerous heat impact. Avoiding strenuous work or having [[air conditioning]] is not possible for everybody.{{sfn|Matthews|2018|p=402}} In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control, and genetic improvements for increased tolerance to a changing climate.{{sfn|IPCC SRCCL Ch5|2019|p=439}} Insurance allows for risk-sharing, but is often difficult to get for people on lower incomes.<ref>{{Cite journal |last1=Surminski |first1=Swenja |last2=Bouwer |first2=Laurens M. |last3=Linnerooth-Bayer |first3=Joanne |date=2016 |title=How insurance can support climate resilience |url=https://www.nature.com/articles/nclimate2979 |journal=[[Nature Climate Change]] |volume=6 |issue=4 |pages=333–334 |doi=10.1038/nclimate2979 |bibcode=2016NatCC...6..333S |issn=1758-6798}}</ref> Education, migration and [[early warning system]]s can reduce climate vulnerability.{{sfn|IPCC SR15 Ch4|2018|pp=336–337}} Planting mangroves or encouraging other coastal vegetation can buffer storms.<ref>{{Cite web |last= |first= |title=Mangroves against the storm |url=https://social.shorthand.com/IUCN_forests/nCec1jyqvn/mangroves-against-the-storm.html |access-date=20 January 2023 |website=Shorthand |language=en}}</ref><ref>{{Cite web |title=How marsh grass could help protect us from climate change |url=https://www.weforum.org/agenda/2021/10/how-marsh-grass-protects-shorelines/ |access-date=20 January 2023 |website=World Economic Forum |date=24 October 2021 |language=en}}</ref>
Adaptation to sea level rise consists of avoiding at-risk areas, learning to live with increased flooding, and building [[flood control]]s. If that fails, [[managed retreat]] may be needed.<ref>{{Cite journal |last1=Stephens |first1=Scott A. |last2=Bell |first2=Robert G. |last3=Lawrence |first3=Judy |year=2018 |title=Developing signals to trigger adaptation to sea-level rise |journal=[[Environmental Research Letters]] |volume=13 |issue=10 |at=104004 |doi=10.1088/1748-9326/aadf96 |bibcode=2018ERL....13j4004S |issn=1748-9326 |doi-access=free}}</ref> There are economic barriers for tackling dangerous heat impact. Avoiding strenuous work or having [[air conditioning]] is not possible for everybody.{{sfn|Matthews|2018|p=402}} In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control, and genetic improvements for increased tolerance to a changing climate.{{sfn|IPCC SRCCL Ch5|2019|p=439}} Insurance allows for risk-sharing, but is often difficult to get for people on lower incomes.<ref>{{Cite journal |last1=Surminski |first1=Swenja |last2=Bouwer |first2=Laurens M. |last3=Linnerooth-Bayer |first3=Joanne |year=2016 |title=How insurance can support climate resilience |url=https://www.nature.com/articles/nclimate2979 |journal=[[Nature Climate Change]] |volume=6 |issue=4 |pages=333–334 |doi=10.1038/nclimate2979 |bibcode=2016NatCC...6..333S |issn=1758-6798}}</ref> Education, migration and [[early warning system]]s can reduce climate vulnerability.{{sfn|IPCC SR15 Ch4|2018|pp=336–337}} Planting mangroves or encouraging other coastal vegetation can buffer storms.<ref>{{Cite web |title=Mangroves against the storm |url=https://social.shorthand.com/IUCN_forests/nCec1jyqvn/mangroves-against-the-storm.html |access-date=20 January 2023 |website=Shorthand |language=en}}</ref><ref>{{Cite web |title=How marsh grass could help protect us from climate change |url=https://www.weforum.org/agenda/2021/10/how-marsh-grass-protects-shorelines/ |access-date=20 January 2023 |website=World Economic Forum |date=24 October 2021 |language=en}}</ref>


Ecosystems adapt to climate change, a process that can be supported by human intervention. By increasing connectivity between ecosystems, species can migrate to more favourable climate conditions. Species can also be [[Assisted migration|introduced to areas acquiring a favourable climate]]. Protection and restoration of natural and semi-natural areas helps build resilience, making it easier for ecosystems to adapt. Many of the actions that promote adaptation in ecosystems, also help humans adapt via [[ecosystem-based adaptation]]. For instance, restoration of [[Fire regime|natural fire regimes]] makes catastrophic fires less likely, and reduces human exposure. Giving rivers more space allows for more water storage in the natural system, reducing flood risk. Restored forest acts as a carbon sink, but planting trees in unsuitable regions can exacerbate climate impacts.<ref>{{Cite journal |last1=Morecroft |first1=Michael D. |last2=Duffield |first2=Simon |last3=Harley |first3=Mike |last4=Pearce-Higgins |first4=James W. |last5=Stevens |first5=Nicola |last6=Watts |first6=Olly |last7=Whitaker |first7=Jeanette |display-authors=4 |date=2019 |title=Measuring the success of climate change adaptation and mitigation in terrestrial ecosystems |journal=[[Science (journal)|Science]] |volume=366 |issue=6471 |page=eaaw9256 |doi=10.1126/science.aaw9256 |issn=0036-8075 |pmid=31831643 |s2cid=209339286 |doi-access=free}}</ref>
Ecosystems adapt to climate change, a process that can be supported by human intervention. By increasing connectivity between ecosystems, species can migrate to more favourable climate conditions. Species can also be [[Assisted migration|introduced to areas acquiring a favourable climate]]. Protection and restoration of natural and semi-natural areas helps build resilience, making it easier for ecosystems to adapt. Many of the actions that promote adaptation in ecosystems, also help humans adapt via [[ecosystem-based adaptation]]. For instance, restoration of [[Fire regime|natural fire regimes]] makes catastrophic fires less likely, and reduces human exposure. Giving rivers more space allows for more water storage in the natural system, reducing flood risk. Restored forest acts as a carbon sink, but planting trees in unsuitable regions can exacerbate climate impacts.<ref>{{Cite journal |last1=Morecroft |first1=Michael D. |last2=Duffield |first2=Simon |last3=Harley |first3=Mike |last4=Pearce-Higgins |first4=James W. |last5=Stevens |first5=Nicola |last6=Watts |first6=Olly |last7=Whitaker |first7=Jeanette |display-authors=4 |year=2019 |title=Measuring the success of climate change adaptation and mitigation in terrestrial ecosystems |journal=[[Science (journal)|Science]] |volume=366 |issue=6471 |page=eaaw9256 |doi=10.1126/science.aaw9256 |issn=0036-8075 |pmid=31831643 |s2cid=209339286 |doi-access=free}}</ref>


There are [[Synergy|synergies]] but also trade-offs between adaptation and mitigation.<ref>{{Cite journal |last1=Berry |first1=Pam M. |last2=Brown |first2=Sally |last3=Chen |first3=Minpeng |last4=Kontogianni |first4=Areti |last5=Rowlands |first5=Olwen |last6=Simpson |first6=Gillian |last7=Skourtos |first7=Michalis |display-authors=4 |date=2015 |title=Cross-sectoral interactions of adaptation and mitigation measures |url=https://doi.org/10.1007/s10584-014-1214-0 |journal=[[Climatic Change (journal)|Climate Change]] |volume=128 |issue=3 |pages=381–393 |bibcode=2015ClCh..128..381B |doi=10.1007/s10584-014-1214-0 |issn=1573-1480 |s2cid=153904466|hdl=10.1007/s10584-014-1214-0 |hdl-access=free }}</ref> An example for synergy is increased food productivity, which has large benefits for both adaptation and mitigation.<ref>{{Harvnb|IPCC AR5 SYR|2014|p=54}}.</ref> An example of a trade-off is that increased use of air conditioning allows people to better cope with heat, but increases energy demand. Another trade-off example is that more compact [[Urban planning|urban development]] may reduce emissions from transport and construction, but may also increase the [[urban heat island]] effect, exposing people to heat-related health risks.<ref>{{Cite journal |last=Sharifi |first=Ayyoob |date=2020 |title=Trade-offs and conflicts between urban climate change mitigation and adaptation measures: A literature review |journal=Journal of Cleaner Production |volume=276 |page=122813 |doi=10.1016/j.jclepro.2020.122813 |bibcode=2020JCPro.27622813S |s2cid=225638176 |issn=0959-6526 |url=http://www.sciencedirect.com/science/article/pii/S0959652620328584}}</ref>
There are [[Synergy|synergies]] but also trade-offs between adaptation and mitigation.<ref>{{Cite journal |last1=Berry |first1=Pam M. |last2=Brown |first2=Sally |last3=Chen |first3=Minpeng |last4=Kontogianni |first4=Areti |last5=Rowlands |first5=Olwen |last6=Simpson |first6=Gillian |last7=Skourtos |first7=Michalis |display-authors=4 |year=2015 |title=Cross-sectoral interactions of adaptation and mitigation measures |url=https://doi.org/10.1007/s10584-014-1214-0 |journal=[[Climatic Change (journal)|Climate Change]] |volume=128 |issue=3 |pages=381–393 |bibcode=2015ClCh..128..381B |doi=10.1007/s10584-014-1214-0 |issn=1573-1480 |s2cid=153904466|hdl=10.1007/s10584-014-1214-0 |hdl-access=free }}</ref> An example for synergy is increased food productivity, which has large benefits for both adaptation and mitigation.<ref>{{Harvnb|IPCC AR5 SYR|2014|p=54}}.</ref> An example of a trade-off is that increased use of air conditioning allows people to better cope with heat, but increases energy demand. Another trade-off example is that more compact [[Urban planning|urban development]] may reduce emissions from transport and construction, but may also increase the [[urban heat island]] effect, exposing people to heat-related health risks.<ref>{{Cite journal |last=Sharifi |first=Ayyoob |year=2020 |title=Trade-offs and conflicts between urban climate change mitigation and adaptation measures: A literature review |journal=Journal of Cleaner Production |volume=276 |page=122813 |doi=10.1016/j.jclepro.2020.122813 |bibcode=2020JCPro.27622813S |s2cid=225638176 |issn=0959-6526 |url=http://www.sciencedirect.com/science/article/pii/S0959652620328584}}</ref>


{| class="center toccolours"
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=== Policy options ===
=== Policy options ===
{{Further|Climate policy}}
A wide range of [[Policy|policies]], [[regulation]]s, and laws are being used to reduce emissions. As of 2019, [[carbon pricing]] covers about 20% of global greenhouse gas emissions.<ref>{{harvnb|World Bank, June|2019|p=12|loc=Box 1}}</ref> Carbon can be priced with [[carbon tax]]es and [[Carbon emission trading|emissions trading systems]].<ref>{{harvnb|Union of Concerned Scientists, 8 January|2017}}; {{harvnb|Hagmann|Ho|Loewenstein|2019}}.</ref> Direct global [[fossil fuel subsidies]] reached $319 billion in 2017, and $5.2 trillion when indirect costs such as air pollution are priced in.<ref>{{harvnb|Watts|Amann|Arnell|Ayeb-Karlsson|2019|p=1866}}</ref> Ending these can cause a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths.<ref>{{harvnb|UN Human Development Report|2020|p=10}}</ref> Money saved on fossil subsidies could be used to support the [[Renewable energy transition|transition to clean energy]] instead.<ref>{{harvnb|International Institute for Sustainable Development|2019|p=iv}}</ref> More direct methods to reduce greenhouse gases include vehicle efficiency standards, renewable fuel standards, and air pollution regulations on heavy industry.<ref>{{harvnb|ICCT|2019|p=iv}}; {{harvnb|Natural Resources Defense Council, 29 September|2017}}</ref> Several countries [[Renewable portfolio standard|require utilities to increase the share of renewables in power production]].<ref>{{harvnb|National Conference of State Legislators, 17 April|2020}}; {{harvnb|European Parliament, February|2020}}</ref>
A wide range of [[Policy|policies]], [[regulation]]s, and laws are being used to reduce emissions. As of 2019, [[carbon pricing]] covers about 20% of global greenhouse gas emissions.<ref>{{harvnb|World Bank, June|2019|p=12|loc=Box 1}}</ref> Carbon can be priced with [[carbon tax]]es and [[Carbon emission trading|emissions trading systems]].<ref>{{harvnb|Union of Concerned Scientists, 8 January|2017}}; {{harvnb|Hagmann|Ho|Loewenstein|2019}}.</ref> Direct global [[fossil fuel subsidies]] reached $319&nbsp;billion in 2017, and $5.2&nbsp;trillion when indirect costs such as air pollution are priced in.<ref>{{harvnb|Watts|Amann|Arnell|Ayeb-Karlsson|2019|p=1866}}</ref> Ending these can cause a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths.<ref>{{harvnb|UN Human Development Report|2020|p=10}}</ref> Money saved on fossil subsidies could be used to support the [[Renewable energy transition|transition to clean energy]] instead.<ref>{{harvnb|International Institute for Sustainable Development|2019|p=iv}}</ref> More direct methods to reduce greenhouse gases include vehicle efficiency standards, renewable fuel standards, and air pollution regulations on heavy industry.<ref>{{harvnb|ICCT|2019|p=iv}}; {{harvnb|Natural Resources Defense Council, 29 September|2017}}</ref> Several countries [[Renewable portfolio standard|require utilities to increase the share of renewables in power production]].<ref>{{harvnb|National Conference of State Legislators, 17 April|2020}}; {{harvnb|European Parliament, February|2020}}</ref>


==== Climate justice ====
==== Climate justice ====
Policy designed through the lens of [[climate justice]] tries to address [[human rights]] issues and social inequality. According to proponents of climate justice, the costs of climate adaptation should be paid by those most responsible for climate change, while the beneficiaries of payments should be those suffering impacts. One way this can be addressed in practice is to have wealthy nations pay poorer countries to adapt.<ref>{{harvnb|Carbon Brief, 16 October|2021}}</ref>
Policy designed through the lens of [[climate justice]] tries to address [[human rights]] issues and social inequality. According to proponents of climate justice, the costs of climate adaptation should be paid by those most responsible for climate change, while the beneficiaries of payments should be those suffering impacts. One way this can be addressed in practice is to have wealthy nations pay poorer countries to adapt.<ref>{{harvnb|Carbon Brief, 16 October|2021}}</ref>


Oxfam found that in 2023 the wealthiest 10% of people were responsible for 50% of global emissions, while the bottom 50% were responsible for just 8%.<ref>{{Cite journal|title=Climate Equality: A planet for the 99% |last1=Khalfan|first1=Ashfaq|last2=Lewis|first2=Astrid Nilsson|last3=Aguilar|first3=Carlos|last4=Persson|first4=Jacqueline|last5=Lawson|first5=Max|last6=Dab|first6=Nafkote|last7=Jayoussi|first7=Safa|last8=Acharya|first8=Sunil|date=November 2023|publisher=Oxfam GB |website=Oxfam Digital Repository |doi=10.21201/2023.000001|url=https://oxfamilibrary.openrepository.com/bitstream/handle/10546/621551/cr-climate-equality-201123-en-summ.pdf|access-date=18 December 2023}}</ref> Production of emissions is another way to look at responsibility: under that approach, the top 21 fossil fuel companies would owe cumulative [[climate reparations]] of $5.4 trillion over the period 2025–2050.<ref name=OneEarth_20230519>{{cite journal |last1=Grasso |first1=Marco |last2=Heede |first2=Richard |title=Time to pay the piper: Fossil fuel companies' reparations for climate damages |journal=One Earth |date=19 May 2023 |volume=6 |issue=5 |pages=459–463 |doi=10.1016/j.oneear.2023.04.012 |bibcode=2023OEart...6..459G |bibcode-access=free |s2cid=258809532 |s2cid-access=free |doi-access=free |hdl=10281/416137 |hdl-access=free }}</ref> To achieve a [[just transition]], people working in the fossil fuel sector would also need other jobs, and their communities would need investments.<ref>{{harvnb|Carbon Brief, 4 Jan|2017}}.</ref>
Oxfam found that in 2023 the wealthiest 10% of people were responsible for 50% of global emissions, while the bottom 50% were responsible for just 8%.<ref>{{Cite journal|title=Climate Equality: A planet for the 99% |last1=Khalfan|first1=Ashfaq|last2=Lewis|first2=Astrid Nilsson|last3=Aguilar|first3=Carlos|last4=Persson|first4=Jacqueline|last5=Lawson|first5=Max|last6=Dab|first6=Nafkote|last7=Jayoussi|first7=Safa|last8=Acharya|first8=Sunil|date=November 2023|website=Oxfam Digital Repository |publisher=Oxfam GB |doi=10.21201/2023.000001|url=https://oxfamilibrary.openrepository.com/bitstream/handle/10546/621551/cr-climate-equality-201123-en-summ.pdf|access-date=18 December 2023}}</ref> Production of emissions is another way to look at responsibility: under that approach, the top 21 fossil fuel companies would owe cumulative [[climate reparations]] of $5.4&nbsp;trillion over the period 2025–2050.<ref name=OneEarth_20230519>{{cite journal |last1=Grasso |first1=Marco |last2=Heede |first2=Richard |title=Time to pay the piper: Fossil fuel companies' reparations for climate damages |journal=One Earth |date=19 May 2023 |volume=6 |issue=5 |pages=459–463 |doi=10.1016/j.oneear.2023.04.012 |bibcode=2023OEart...6..459G |bibcode-access=free |s2cid=258809532 |s2cid-access=free |doi-access=free |hdl=10281/416137 |hdl-access=free }}</ref> To achieve a [[just transition]], people working in the fossil fuel sector would also need other jobs, and their communities would need investments.<ref>{{harvnb|Carbon Brief, 4 Jan|2017}}.</ref>


=== International climate agreements ===
=== International climate agreements ===
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[[File:Total CO2 by Region.svg|thumb|upright=1.35|Since 2000, rising {{CO2}} emissions in China and the rest of world have surpassed the output of the United States and Europe.<ref name="Friedlingstein 2019">{{harvnb|Friedlingstein|Jones|O'Sullivan|Andrew|2019}}, Table 7.</ref>]]
[[File:Total CO2 by Region.svg|thumb|upright=1.35|Since 2000, rising {{CO2}} emissions in China and the rest of world have surpassed the output of the United States and Europe.<ref name="Friedlingstein 2019">{{harvnb|Friedlingstein|Jones|O'Sullivan|Andrew|2019}}, Table 7.</ref>]]
[[File:Per Capita CO2 by Region.svg|thumb|upright=1.35|Per person, the United States generates {{CO2}} at a far faster rate than other primary regions.<ref name="Friedlingstein 2019"/>]]
[[File:Per Capita CO2 by Region.svg|thumb|upright=1.35|Per person, the United States generates {{CO2}} at a far faster rate than other primary regions.<ref name="Friedlingstein 2019"/>]]
Nearly all countries in the world are parties to the 1994 [[United Nations Framework Convention on Climate Change]] (UNFCCC).<ref>{{harvnb|UNFCCC, "What is the United Nations Framework Convention on Climate Change?"}}</ref> The goal of the UNFCCC is to prevent dangerous human interference with the climate system.<ref>{{harvnb|UNFCCC|1992|loc=Article 2}}.</ref> As stated in the convention, this requires that greenhouse gas concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and [[Economics of climate change|economic development]] can be sustained.<ref>{{Harvnb|IPCC AR4 WG3 Ch1|2007|p=97}}.</ref> The UNFCCC does not itself restrict emissions but rather provides a framework for protocols that do. Global emissions have risen since the UNFCCC was signed.<ref name="EPA-2019">{{harvnb|EPA|2019}}.</ref> [[United Nations Climate Change conference|Its yearly conferences]] are the stage of global negotiations.<ref>{{harvnb|UNFCCC, "What are United Nations Climate Change Conferences?"}}</ref>
Nearly all countries in the world are parties to the 1994 [[United Nations Framework Convention on Climate Change]] (UNFCCC).<ref>{{harvnb|UNFCCC, "What is the United Nations Framework Convention on Climate Change?"}}</ref> The goal of the UNFCCC is to prevent dangerous human interference with the climate system.<ref>{{harvnb|UNFCCC|1992|loc=Article 2}}.</ref> As stated in the convention, this requires that greenhouse gas concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and [[Economic analysis of climate change|economic development]] can be sustained.<ref>{{Harvnb|IPCC AR4 WG3 Ch1|2007|p=97}}.</ref> The UNFCCC does not itself restrict emissions but rather provides a framework for protocols that do. Global emissions have risen since the UNFCCC was signed.<ref name="EPA-2019">{{harvnb|EPA|2019}}.</ref> [[United Nations Climate Change conference|Its yearly conferences]] are the stage of global negotiations.<ref>{{harvnb|UNFCCC, "What are United Nations Climate Change Conferences?"}}</ref>


The 1997 [[Kyoto Protocol]] extended the UNFCCC and included legally binding commitments for most developed countries to limit their emissions.<ref>{{harvnb|Kyoto Protocol|1997}}; {{harvnb|Liverman|2009|p=290}}.</ref> During the negotiations, the [[Group of 77|G77]] (representing [[Developing country|developing countries]]) pushed for a mandate requiring [[Developed country|developed countries]] to "[take] the lead" in reducing their emissions,<ref>{{harvnb|Dessai|2001|p=4}}; {{harvnb|Grubb|2003}}.</ref> since developed countries contributed most to the [[Greenhouse gas emissions#Cumulative and historical emissions|accumulation of greenhouse gases]] in the atmosphere. Per-capita emissions were also still relatively low in developing countries and developing countries would need to emit more to meet their development needs.<ref>{{harvnb|Liverman|2009|p=290}}.</ref>
The 1997 [[Kyoto Protocol]] extended the UNFCCC and included legally binding commitments for most developed countries to limit their emissions.<ref>{{harvnb|Kyoto Protocol|1997}}; {{harvnb|Liverman|2009|p=290}}.</ref> During the negotiations, the [[Group of 77|G77]] (representing [[Developing country|developing countries]]) pushed for a mandate requiring [[Developed country|developed countries]] to "[take] the lead" in reducing their emissions,<ref>{{harvnb|Dessai|2001|p=4}}; {{harvnb|Grubb|2003}}.</ref> since developed countries contributed most to the [[Greenhouse gas emissions#Cumulative and historical emissions|accumulation of greenhouse gases]] in the atmosphere. Per-capita emissions were also still relatively low in developing countries and developing countries would need to emit more to meet their development needs.<ref>{{harvnb|Liverman|2009|p=290}}.</ref>


The 2009 [[Copenhagen Accord]] has been widely portrayed as disappointing because of its low goals, and was rejected by poorer nations including the G77.<ref>{{harvnb|Müller|2010}}; {{harvnb|The New York Times, 25 May|2015}}; {{harvnb|UNFCCC: Copenhagen|2009}}; {{harvnb|EUobserver, 20 December|2009}}.</ref> Associated parties aimed to limit the global temperature rise to below 2&nbsp;°C.<ref>{{harvnb|UNFCCC: Copenhagen|2009}}.</ref> The Accord set the goal of sending $100 billion per year to developing countries for mitigation and adaptation by 2020, and proposed the founding of the [[Green Climate Fund]].<ref>{{cite conference |date=7–18 December 2009 |title=Conference of the Parties to the Framework Convention on Climate Change |url=http://unfccc.int/meetings/cop_15/items/5257.php |location=[[Copenhagen]] |id=un document= FCCC/CP/2009/L.7 |archive-url=https://web.archive.org/web/20101018074452/http://unfccc.int/meetings/cop_15/items/5257.php |archive-date=18 October 2010 |access-date=24 October 2010 |url-status=live}}</ref> {{As of|2020|}}, only 83.3 billion were delivered. Only in 2023 the target is expected to be achieved.<ref>{{cite news |last1=Bennett |first1=Paige |title=High-Income Nations Are on Track Now to Meet $100 Billion Climate Pledges, but They're Late |url=https://www.ecowatch.com/wealthy-countries-climate-change-reparations.html |access-date=10 May 2023 |agency=Ecowatch |date=2 May 2023}}</ref>
The 2009 [[Copenhagen Accord]] has been widely portrayed as disappointing because of its low goals, and was rejected by poorer nations including the G77.<ref>{{harvnb|Müller|2010}}; {{harvnb|The New York Times, 25 May|2015}}; {{harvnb|UNFCCC: Copenhagen|2009}}; {{harvnb|EUobserver, 20 December|2009}}.</ref> Associated parties aimed to limit the global temperature rise to below 2&nbsp;°C.<ref>{{harvnb|UNFCCC: Copenhagen|2009}}.</ref> The Accord set the goal of sending $100&nbsp;billion per year to developing countries for mitigation and adaptation by 2020, and proposed the founding of the [[Green Climate Fund]].<ref>{{cite conference |date=7–18 December 2009 |title=Conference of the Parties to the Framework Convention on Climate Change |url=http://unfccc.int/meetings/cop_15/items/5257.php |location=Copenhagen |id=un document= FCCC/CP/2009/L.7 |archive-url=https://web.archive.org/web/20101018074452/http://unfccc.int/meetings/cop_15/items/5257.php |archive-date=18 October 2010 |access-date=24 October 2010 |url-status=live}}</ref> {{As of|2020|}}, only 83.3&nbsp;billion were delivered. Only in 2023 the target is expected to be achieved.<ref>{{cite news |last1=Bennett |first1=Paige |title=High-Income Nations Are on Track Now to Meet $100 Billion Climate Pledges, but They're Late |url=https://www.ecowatch.com/wealthy-countries-climate-change-reparations.html |access-date=10 May 2023 |agency=Ecowatch |date=2 May 2023}}</ref>


In 2015 all UN countries negotiated the [[Paris Agreement]], which aims to keep global warming well below 2.0&nbsp;°C and contains an aspirational goal of keeping warming under {{val|1.5|u=°C}}.{{sfn|Paris Agreement|2015}} The agreement replaced the Kyoto Protocol. Unlike Kyoto, no binding emission targets were set in the Paris Agreement. Instead, a set of procedures was made binding. Countries have to regularly set ever more ambitious goals and reevaluate these goals every five years.<ref>{{harvnb|Climate Focus|2015|p=3}}; {{harvnb|Carbon Brief, 8 October|2018}}.</ref> The Paris Agreement restated that developing countries must be financially supported.<ref>{{harvnb|Climate Focus|2015|p=5}}.</ref> {{As of|October 2021}}, 194 states and the [[European Union]] have signed the treaty and 191 states and the EU have [[Ratification|ratified]] or acceded to the agreement.<ref>{{cite web |title=Status of Treaties, United Nations Framework Convention on Climate Change |url=https://treaties.un.org/Pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en |access-date=13 October 2021 |website=United Nations Treaty Collection}}; {{harvnb|Salon, 25 September|2019}}.</ref>
In 2015 all UN countries negotiated the [[Paris Agreement]], which aims to keep global warming well below 2.0&nbsp;°C and contains an aspirational goal of keeping warming under {{val|1.5|u=°C}}.{{sfn|Paris Agreement|2015}} The agreement replaced the Kyoto Protocol. Unlike Kyoto, no binding emission targets were set in the Paris Agreement. Instead, a set of procedures was made binding. Countries have to regularly set ever more ambitious goals and reevaluate these goals every five years.<ref>{{harvnb|Climate Focus|2015|p=3}}; {{harvnb|Carbon Brief, 8 October|2018}}.</ref> The Paris Agreement restated that developing countries must be financially supported.<ref>{{harvnb|Climate Focus|2015|p=5}}.</ref> {{As of|October 2021}}, 194 states and the [[European Union]] have signed the treaty and 191 states and the EU have [[Ratification|ratified]] or acceded to the agreement.<ref>{{cite web |title=Status of Treaties, United Nations Framework Convention on Climate Change |url=https://treaties.un.org/Pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7-d&chapter=27&clang=_en |access-date=13 October 2021 |website=United Nations Treaty Collection}}; {{harvnb|Salon, 25 September|2019}}.</ref>
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=== National responses ===
=== National responses ===
[[File:Annual-co2-emissions-by-region-2022.png|thumb|260px|Annual [[List of countries by carbon dioxide emissions|{{CO2}} emissions by region]]. This measures fossil fuel and industry emissions. [[Land use change]] is not included.<ref>{{cite web |url=https://ourworldindata.org/grapher/annual-co-emissions-by-region |title=Annual {{CO2}} emissions by world region |publisher=[[Our World in Data]] |website=ourworldindata.org |format=chart|access-date=2024-09-18}}</ref>]]
[[File:Annual-co2-emissions-by-region-2022.png|thumb|260px|Annual [[List of countries by carbon dioxide emissions|{{CO2}} emissions by region]]. This measures fossil fuel and industry emissions. [[Land use change]] is not included.<ref>{{cite web |url=https://ourworldindata.org/grapher/annual-co-emissions-by-region |title=Annual {{CO2}} emissions by world region |website=ourworldindata.org |publisher=[[Our World in Data]] |format=chart|access-date=2024-09-18}}</ref>]]
In 2019, the [[Parliament of the United Kingdom|United Kingdom parliament]] became the first national government to declare a climate emergency.<ref>{{Harvnb|BBC, 1 May|2019}}; {{Harvnb|Vice, 2 May|2019}}.</ref> Other countries and [[jurisdiction]]s followed suit.<ref>{{harvnb|The Verge, 27 December|2019}}.</ref> That same year, the [[European Parliament]] declared a "climate and environmental emergency".<ref>{{harvnb|The Guardian, 28 November|2019}}</ref> The [[European Commission]] presented its [[European Green Deal]] with the goal of making the EU carbon-neutral by 2050.<ref>{{harvnb|Politico, 11 December|2019}}.</ref> In 2021, the European Commission released its "[[Fit for 55]]" legislation package, which contains guidelines for the [[automotive industry|car industry]]; all new cars on the European market must be [[Zero-emissions vehicle|zero-emission vehicles]] from 2035.<ref>{{cite news |title=European Green Deal: Commission proposes transformation of EU economy and society to meet climate ambitions |url=https://ec.europa.eu/commission/presscorner/detail/en/ip_21_3541 |work=[[European Commission]] |date=14 July 2021}}</ref>
In 2019, the [[Parliament of the United Kingdom|United Kingdom parliament]] became the first national government to declare a climate emergency.<ref>{{Harvnb|BBC, 1 May|2019}}; {{Harvnb|Vice, 2 May|2019}}.</ref> Other countries and [[jurisdiction]]s followed suit.<ref>{{harvnb|The Verge, 27 December|2019}}.</ref> That same year, the [[European Parliament]] declared a "climate and environmental emergency".<ref>{{harvnb|The Guardian, 28 November|2019}}</ref> The [[European Commission]] presented its [[European Green Deal]] with the goal of making the EU carbon-neutral by 2050.<ref>{{harvnb|Politico, 11 December|2019}}.</ref> In 2021, the European Commission released its "[[Fit for 55]]" legislation package, which contains guidelines for the [[automotive industry|car industry]]; all new cars on the European market must be [[Zero-emissions vehicle|zero-emission vehicles]] from 2035.<ref>{{cite news |title=European Green Deal: Commission proposes transformation of EU economy and society to meet climate ambitions |url=https://ec.europa.eu/commission/presscorner/detail/en/ip_21_3541 |work=[[European Commission]] |date=14 July 2021}}</ref>


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Public debate about climate change has been strongly affected by climate change denial and [[misinformation]], which originated in the United States and has since spread to other countries, particularly Canada and Australia. Climate change denial has originated from fossil fuel companies, industry groups, [[conservative]] think tanks, and [[contrarian]] scientists.<ref>{{harvnb|Dunlap|McCright|2011|pp=144, [https://books.google.com/books?id=RsYr_iQUs6QC&pg=PA155 155]}}; {{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref> [[Tobacco industry playbook|Like the tobacco industry]], the main strategy of these groups has been to manufacture doubt about climate-change related scientific data and results.<ref>{{harvnb|Oreskes|Conway|2010}}; {{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref> People who hold unwarranted doubt about climate change are called climate change "skeptics", although "contrarians" or "deniers" are more appropriate terms.<ref>{{harvnb|O'Neill|Boykoff|2010}}; {{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref>
Public debate about climate change has been strongly affected by climate change denial and [[misinformation]], which originated in the United States and has since spread to other countries, particularly Canada and Australia. Climate change denial has originated from fossil fuel companies, industry groups, [[conservative]] think tanks, and [[contrarian]] scientists.<ref>{{harvnb|Dunlap|McCright|2011|pp=144, [https://books.google.com/books?id=RsYr_iQUs6QC&pg=PA155 155]}}; {{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref> [[Tobacco industry playbook|Like the tobacco industry]], the main strategy of these groups has been to manufacture doubt about climate-change related scientific data and results.<ref>{{harvnb|Oreskes|Conway|2010}}; {{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref> People who hold unwarranted doubt about climate change are called climate change "skeptics", although "contrarians" or "deniers" are more appropriate terms.<ref>{{harvnb|O'Neill|Boykoff|2010}}; {{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref>


There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimize the negative impacts of climate change.<ref name="Björnberg 2017">{{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref> Manufacturing uncertainty about the science later developed into a [[manufactured controversy]]: creating the belief that there is significant uncertainty about climate change within the scientific community in order to delay policy changes.<ref>{{harvnb|Dunlap|McCright|2015|p=308}}.</ref> Strategies to promote these ideas include criticism of scientific institutions,<ref>{{harvnb|Dunlap|McCright|2011|p=146}}.</ref> and questioning the motives of individual scientists.<ref name="Björnberg 2017"/> An [[echo chamber (media)|echo chamber]] of climate-denying [[blogs]] and media has further fomented misunderstanding of climate change.<ref>{{harvnb|Harvey|Van den Berg|Ellers|Kampen|2018}}</ref>
There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimize the negative impacts of climate change.<ref name="Björnberg 2017">{{harvnb|Björnberg|Karlsson|Gilek|Hansson|2017}}</ref> Manufacturing uncertainty about the science later developed into a [[manufactured controversy]]: creating the belief that there is significant uncertainty about climate change within the scientific community to delay policy changes.<ref>{{harvnb|Dunlap|McCright|2015|p=308}}.</ref> Strategies to promote these ideas include criticism of scientific institutions,<ref>{{harvnb|Dunlap|McCright|2011|p=146}}.</ref> and questioning the motives of individual scientists.<ref name="Björnberg 2017"/> An [[echo chamber (media)|echo chamber]] of climate-denying [[blogs]] and media has further fomented misunderstanding of climate change.<ref>{{harvnb|Harvey|Van den Berg|Ellers|Kampen|2018}}</ref>


=== Public awareness and opinion ===
=== Public awareness and opinion ===
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=== Early discoveries ===
=== Early discoveries ===
[[File:19120814 Coal Consumption Affecting Climate - Rodney and Otamatea Times.jpg|thumb|upright=1.35 |This 1912 article succinctly describes the greenhouse effect, how burning coal creates carbon dioxide to cause global warming and climate change.<ref name="Otamatea Times">{{cite news |date=14 August 1912 |title=Coal Consumption Affecting Climate |page=7 |work=Rodney and Otamatea Times, Waitemata and Kaipara Gazette |location=Warkworth, New Zealand |url=https://paperspast.natlib.govt.nz/newspapers/ROTWKG19120814.2.56.5}} Text was earlier [[:File:191203 Furnaces of the world - Popular Mechanics - Global warming.jpg|published in ''Popular Mechanics'']], March 1912, p. 341.</ref>]]
[[File:19120814 Coal Consumption Affecting Climate - Rodney and Otamatea Times.jpg|thumb|upright=1.35 |This 1912 article succinctly describes the greenhouse effect, how burning coal creates carbon dioxide to cause global warming and climate change.<ref name="Otamatea Times">{{cite news |date=14 August 1912 |title=Coal Consumption Affecting Climate |page=7 |work=Rodney and Otamatea Times, Waitemata and Kaipara Gazette |location=Warkworth, New Zealand |url=https://paperspast.natlib.govt.nz/newspapers/ROTWKG19120814.2.56.5}} Text was earlier [[:File:191203 Furnaces of the world - Popular Mechanics - Global warming.jpg|published in ''Popular Mechanics'']], March 1912, p. 341.</ref>]]
Scientists in the 19th century such as [[Alexander von Humboldt]] began to foresee the effects of climate change.<ref name="Nord 2020 p. 51">{{cite book | last=Nord | first=D.C. | title=Nordic Perspectives on the Responsible Development of the Arctic: Pathways to Action | publisher=Springer International Publishing | series=Springer Polar Sciences | year=2020 | isbn=978-3-030-52324-4 | url=https://books.google.com/books?id=KmMGEAAAQBAJ&pg=PA51 | access-date=11 March 2023 | page=51}}</ref><ref name="Mukherjee Scanlon Aureli Langan 2020 p. 331">{{cite book | last1=Mukherjee | first1=A. | last2=Scanlon | first2=B.R. | last3=Aureli | first3=A. | last4=Langan | first4=S. | last5=Guo | first5=H. | last6=McKenzie | first6=A.A. | title=Global Groundwater: Source, Scarcity, Sustainability, Security, and Solutions | publisher=Elsevier Science | year=2020 | isbn=978-0-12-818173-7 | url=https://books.google.com/books?id=17vbDwAAQBAJ&pg=PA331 | access-date=11 March 2023 | page=331}}</ref><ref name="von Humboldt Wulf 2018 p. 10">{{cite book | last1=von Humboldt | first1=A. | last2=Wulf | first2=A. | title=Selected Writings of Alexander von Humboldt: Edited and Introduced by Andrea Wulf | publisher=Knopf Doubleday Publishing Group | series=Everyman's Library Classics Series | year=2018 | isbn=978-1-101-90807-5 | url=https://books.google.com/books?id=xal2DwAAQBAJ&pg=PR10 | access-date=11 March 2023 | page=10}}</ref><ref name="Erdkamp Manning Verboven 2021 p. 6">{{cite book | last1=Erdkamp | first1=P. | last2=Manning | first2=J.G. | last3=Verboven | first3=K. | title=Climate Change and Ancient Societies in Europe and the Near East: Diversity in Collapse and Resilience | publisher=Springer International Publishing | series=Palgrave Studies in Ancient Economies | year=2021 | isbn=978-3-030-81103-7 | url=https://books.google.com/books?id=ZbdMEAAAQBAJ&pg=PR6 | access-date=11 March 2023 | page=6}}</ref> In the 1820s, [[Joseph Fourier]] proposed the greenhouse effect to explain why Earth's temperature was higher than the Sun's energy alone could explain. Earth's atmosphere is transparent to sunlight, so sunlight reaches the surface where it is converted to heat. However, the atmosphere is not transparent to heat radiating from the surface, and captures some of that heat, which in turn warms the planet.<ref>{{harvnb|Archer|Pierrehumbert|2013|pp=[https://books.google.com/books?id=sPY9HOfnuS0C&pg=PA10 10–14]}}</ref>
Scientists in the 19th century such as [[Alexander von Humboldt]] began to foresee the effects of climate change.<ref name="Nord 2020 p. 51">{{cite book |last=Nord |first=D. C. |url=https://books.google.com/books?id=KmMGEAAAQBAJ&pg=PA51 |title=Nordic Perspectives on the Responsible Development of the Arctic: Pathways to Action |publisher=Springer International Publishing |year=2020 |isbn=978-3-030-52324-4 |series=Springer Polar Sciences |page=51 |access-date=11 March 2023}}</ref><ref name="Mukherjee Scanlon Aureli Langan 2020 p. 331">{{cite book |last1=Mukherjee |first1=A. |url=https://books.google.com/books?id=17vbDwAAQBAJ&pg=PA331 |title=Global Groundwater: Source, Scarcity, Sustainability, Security, and Solutions |last2=Scanlon |first2=B. R. |last3=Aureli |first3=A. |last4=Langan |first4=S. |last5=Guo |first5=H. |last6=McKenzie |first6=A. A. |publisher=Elsevier Science |year=2020 |isbn=978-0-12-818173-7 |page=331 |access-date=11 March 2023}}</ref><ref name="von Humboldt Wulf 2018 p. 10">{{cite book | last1=von Humboldt | first1=A. | last2=Wulf | first2=A. | title=Selected Writings of Alexander von Humboldt: Edited and Introduced by Andrea Wulf | publisher=Knopf Doubleday Publishing Group | series=Everyman's Library Classics Series | year=2018 | isbn=978-1-101-90807-5 | url=https://books.google.com/books?id=xal2DwAAQBAJ&pg=PR10 | access-date=11 March 2023 | page=10}}</ref><ref name="Erdkamp Manning Verboven 2021 p. 6">{{cite book |last1=Erdkamp |first1=Paul |url=https://books.google.com/books?id=ZbdMEAAAQBAJ&pg=PR6 |title=Climate Change and Ancient Societies in Europe and the Near East: Diversity in Collapse and Resilience |last2=Manning |first2=Joseph G. |author-link2=Joseph Manning (historian) |last3=Verboven |first3=Koenraad |publisher=Springer International Publishing |year=2021 |isbn=978-3-030-81103-7 |series=Palgrave Studies in Ancient Economies |page=6 |access-date=11 March 2023}}</ref> In the 1820s, [[Joseph Fourier]] proposed the greenhouse effect to explain why Earth's temperature was higher than the Sun's energy alone could explain. Earth's atmosphere is transparent to sunlight, so sunlight reaches the surface where it is converted to heat. However, the atmosphere is not transparent to heat radiating from the surface, and captures some of that heat, which in turn warms the planet.<ref>{{harvnb|Archer|Pierrehumbert|2013|pp=[https://books.google.com/books?id=sPY9HOfnuS0C&pg=PA10 10–14]}}</ref>


In 1856 [[Eunice Newton Foote]] demonstrated that the warming effect of the Sun is greater for air with water vapour than for dry air, and that the effect is even greater with carbon dioxide ({{co2}}). She concluded that "An atmosphere of that gas would give to our earth a high temperature..."<ref>{{cite journal |url=https://books.google.com/books?id=6xhFAQAAMAAJ&pg=PA382 |last=Foote |first=Eunice |title=Circumstances affecting the Heat of the Sun's Rays |journal=The American Journal of Science and Arts |date=November 1856 |volume=22 |pages=382–383 |access-date=31 January 2016 |via=[[Google Books]]}}</ref><ref>{{harvnb|Huddleston|2019}}</ref>
In 1856 [[Eunice Newton Foote]] demonstrated that the warming effect of the Sun is greater for air with water vapour than for dry air, and that the effect is even greater with carbon dioxide ({{co2}}). She concluded that "An atmosphere of that gas would give to our earth a high temperature..."<ref>{{cite journal |url=https://books.google.com/books?id=6xhFAQAAMAAJ&pg=PA382 |last=Foote |first=Eunice |title=Circumstances affecting the Heat of the Sun's Rays |journal=The American Journal of Science and Arts |date=November 1856 |volume=22 |pages=382–383 |access-date=31 January 2016 |via=[[Google Books]]}}</ref><ref>{{harvnb|Huddleston|2019}}</ref>
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=== Development of a scientific consensus ===
=== Development of a scientific consensus ===
{{see also|Scientific consensus on climate change}}
{{see also|Scientific consensus on climate change}}
[[File:20211103 Academic studies of scientific consensus - global warming, climate change - vertical bar chart - en.svg|thumb|right |upright=1.35 |''Scientific consensus on causation:'' Academic studies of scientific agreement on human-caused global warming among climate experts (2010–2015) reflect that the level of consensus correlates with expertise in climate science.<ref>{{cite journal |last1=Cook |first1=John |last2=Oreskes |first2= Naomi |last3=Doran |first3=Peter T. |last4=Anderegg |first4=William R. L. |last5=Verheggen |first5=Bart |display-authors=4 |date=2016 |title=Consensus on consensus: a synthesis of consensus estimates on human-caused global warming |journal=[[Environmental Research Letters]] |volume=11 |issue=4 |page=048002 |bibcode= 2016ERL....11d8002C |doi= 10.1088/1748-9326/11/4/048002 |doi-access=free|hdl=1983/34949783-dac1-4ce7-ad95-5dc0798930a6 |hdl-access=free }}</ref> A 2019 study found scientific consensus to be at 100%,<ref name="Powell2019" /> and a 2021 study concluded that consensus exceeded 99%.<ref name="Lynas2021" /> Another 2021 study found that 98.7% of climate experts indicated that the Earth is getting warmer mostly because of human activity.<ref name="Myers2021">{{cite journal |last1=Myers |first1=Krista F. |last2= Doran |first2=Peter T. |last3=Cook |first3=John |last4=Kotcher |first4=John E. |last5=Myers |first5=Teresa A. |title=Consensus revisited: quantifying scientific agreement on climate change and climate expertise among Earth scientists 10 years later |journal= [[Environmental Research Letters]] |date=20 October 2021 |volume=16 |issue=10 |page=104030 |doi= 10.1088/1748-9326/ac2774 |bibcode= 2021ERL....16j4030M |s2cid= 239047650 |doi-access=free}}</ref>]]
[[File:20211103 Academic studies of scientific consensus - global warming, climate change - vertical bar chart - en.svg|thumb|right |upright=1.35 |''Scientific consensus on causation:'' Academic studies of scientific agreement on human-caused global warming among climate experts (2010–2015) reflect that the level of consensus correlates with expertise in climate science.<ref>{{cite journal |last1=Cook |first1=John |last2=Oreskes |first2= Naomi |last3=Doran |first3=Peter T. |last4=Anderegg |first4=William R. L. |last5=Verheggen |first5=Bart |display-authors=4 |year=2016 |title=Consensus on consensus: a synthesis of consensus estimates on human-caused global warming |journal=[[Environmental Research Letters]] |volume=11 |issue=4 |page=048002 |bibcode= 2016ERL....11d8002C |doi= 10.1088/1748-9326/11/4/048002 |doi-access=free|hdl=1983/34949783-dac1-4ce7-ad95-5dc0798930a6 |hdl-access=free }}</ref> A 2019 study found scientific consensus to be at 100%,<ref name="Powell2019" /> and a 2021 study concluded that consensus exceeded 99%.<ref name="Lynas2021" /> Another 2021 study found that 98.7% of climate experts indicated that the Earth is getting warmer mostly because of human activity.<ref name="Myers2021">{{cite journal |last1=Myers |first1=Krista F. |last2= Doran |first2=Peter T. |last3=Cook |first3=John |last4=Kotcher |first4=John E. |last5=Myers |first5=Teresa A. |title=Consensus revisited: quantifying scientific agreement on climate change and climate expertise among Earth scientists 10 years later |journal= [[Environmental Research Letters]] |date=20 October 2021 |volume=16 |issue=10 |page=104030 |doi= 10.1088/1748-9326/ac2774 |bibcode= 2021ERL....16j4030M |s2cid= 239047650 |doi-access=free}}</ref>]]
In the 1950s, [[Gilbert Plass]] created a detailed computer model that included different atmospheric layers and the infrared spectrum. This model predicted that increasing {{co2}} levels would cause warming. Around the same time, [[Hans Suess]] found evidence that {{co2}} levels had been rising, and [[Roger Revelle]] showed that the oceans would not absorb the increase. The two scientists subsequently helped [[Charles David Keeling|Charles Keeling]] to begin a record of continued increase, which has been termed the "[[Keeling Curve]]".<ref name="Weart The Carbon Dioxide Greenhouse Effect" /> Scientists alerted the public,<ref>{{harvnb|Weart "Suspicions of a Human-Caused Greenhouse (1956–1969)"}}</ref> and the dangers were highlighted at James Hansen's 1988 Congressional testimony.<ref name="history.aip.org2"/> The [[Intergovernmental Panel on Climate Change]] (IPCC), set up in 1988 to provide formal advice to the world's governments, spurred [[Interdisciplinarity|interdisciplinary research]].<ref>{{harvnb|Weart|2013|p=3567}}.</ref> As part of the [[Intergovernmental Panel on Climate Change#Assessment reports|IPCC reports]], scientists assess the scientific discussion that takes place in [[Peer review|peer-reviewed]] [[Scientific journal|journal]] articles.<ref>{{harvnb|Royal Society|2005}}.</ref>
In the 1950s, [[Gilbert Plass]] created a detailed computer model that included different atmospheric layers and the infrared spectrum. This model predicted that increasing {{co2}} levels would cause warming. Around the same time, [[Hans Suess]] found evidence that {{co2}} levels had been rising, and [[Roger Revelle]] showed that the oceans would not absorb the increase. The two scientists subsequently helped [[Charles David Keeling|Charles Keeling]] to begin a record of continued increase, which has been termed the "[[Keeling Curve]]".<ref name="Weart The Carbon Dioxide Greenhouse Effect" /> Scientists alerted the public,<ref>{{harvnb|Weart "Suspicions of a Human-Caused Greenhouse (1956–1969)"}}</ref> and the dangers were highlighted at James Hansen's 1988 Congressional testimony.<ref name="history.aip.org2"/> The [[Intergovernmental Panel on Climate Change]] (IPCC), set up in 1988 to provide formal advice to the world's governments, spurred [[Interdisciplinarity|interdisciplinary research]].<ref>{{harvnb|Weart|2013|p=3567}}.</ref> As part of the [[Intergovernmental Panel on Climate Change#Assessment reports|IPCC reports]], scientists assess the scientific discussion that takes place in [[Peer review|peer-reviewed]] [[Scientific journal|journal]] articles.<ref>{{harvnb|Royal Society|2005}}.</ref>


There is a near-complete scientific consensus that the climate is warming and that this is caused by human activities. As of 2019, agreement in recent literature reached over 99%.<ref name="Powell2019">{{cite journal |last1=Powell |first1=James |date=20 November 2019 |title=Scientists Reach 100% Consensus on Anthropogenic Global Warming |url=https://journals.sagepub.com/doi/abs/10.1177/0270467619886266?journalCode=bsta |journal=[[Bulletin of Science, Technology & Society]] |volume=37 |issue=4 |pages=183–184 |doi=10.1177/0270467619886266 |access-date=15 November 2020 |s2cid=213454806}}</ref><ref name="Lynas2021">{{Cite journal |last1=Lynas |first1=Mark |last2=Houlton |first2=Benjamin Z |last3=Perry |first3=Simon |date=2021 |title=Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature |journal=[[Environmental Research Letters]] |volume=16 |issue=11 |pages=114005 |bibcode=2021ERL....16k4005L |doi=10.1088/1748-9326/ac2966 |issn=1748-9326 |s2cid=239032360|doi-access=free }}</ref> No scientific body of national or international standing [[Scientific consensus on climate change#Opposing|disagrees with this view]].<ref>{{harvnb|National Academies|2008|p=2}}; {{harvnb|Oreskes|2007|p=[https://books.google.com/books?id=PXJIqCkb7YIC&pg=PA68 68]}}; {{Harvnb|Gleick, 7 January|2017}}</ref> Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change. National science academies have called on world leaders to cut global emissions.<ref>Joint statement of the {{harvtxt|G8+5 Academies|2009}}; {{harvnb|Gleick, 7 January|2017}}.</ref> The 2021 IPCC Assessment Report stated that it is "unequivocal" that climate change is caused by humans.<ref name="Lynas2021"/>
There is a near-complete scientific consensus that the climate is warming and that this is caused by human activities. As of 2019, agreement in recent literature reached over 99%.<ref name="Powell2019">{{cite journal |last1=Powell |first1=James |date=20 November 2019 |title=Scientists Reach 100% Consensus on Anthropogenic Global Warming |url=https://journals.sagepub.com/doi/abs/10.1177/0270467619886266?journalCode=bsta |journal=[[Bulletin of Science, Technology & Society]] |volume=37 |issue=4 |pages=183–184 |doi=10.1177/0270467619886266 |access-date=15 November 2020 |s2cid=213454806}}</ref><ref name="Lynas2021">{{Cite journal |last1=Lynas |first1=Mark |last2=Houlton |first2=Benjamin Z |last3=Perry |first3=Simon |year=2021 |title=Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature |journal=[[Environmental Research Letters]] |volume=16 |issue=11 |pages=114005 |bibcode=2021ERL....16k4005L |doi=10.1088/1748-9326/ac2966 |issn=1748-9326 |s2cid=239032360|doi-access=free }}</ref> No scientific body of national or international standing [[Scientific consensus on climate change#Opposing|disagrees with this view]].<ref>{{harvnb|National Academies|2008|p=2}}; {{harvnb|Oreskes|2007|p=[https://books.google.com/books?id=PXJIqCkb7YIC&pg=PA68 68]}}; {{Harvnb|Gleick, 7 January|2017}}</ref> Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change. National science academies have called on world leaders to cut global emissions.<ref>Joint statement of the {{harvtxt|G8+5 Academies|2009}}; {{harvnb|Gleick, 7 January|2017}}.</ref> The 2021 IPCC Assessment Report stated that it is "unequivocal" that climate change is caused by humans.<ref name="Lynas2021"/>


== See also ==
== See also ==
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* [[Anthropocene]] – proposed geological time interval in which humans are having significant geological impact
* [[Anthropocene]] – proposed geological time interval in which humans are having significant geological impact
* [[List of climate scientists]]
* [[List of climate scientists]]
* [[Charney Report]]
{{clear right}}
{{clear right}}


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|url=https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Full_Report_High_Res.pdf
|url=https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Full_Report_High_Res.pdf
}} [https://www.ipcc.ch/sr15/ Global Warming of 1.5 °C –].
}} Global Warming of 1.5 °C –.
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|url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_FullReport_small.pdf
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{{refend}}
{{refend}}


==== Other peer-reviewed sources ====
==== Other peer-reviewed sources ====
{{refbegin|30em}}
{{refbegin|30em}}
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* ''[[EPA]]''
* ''[[EPA]]''
** {{cite web |ref={{harvid|EPA|2016}} |title=Myths vs. Facts: Denial of Petitions for Reconsideration of the Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act |publisher=U.S. Environmental Protection Agency |date=10 September 2020 |url=https://www.epa.gov/ghgemissions/myths-vs-facts-denial-petitions-reconsideration-endangerment-and-cause-or-contribute |access-date=7 August 2017 |archive-url=https://web.archive.org/web/20210523211147/https://www.epa.gov/ghgemissions/myths-vs-facts-denial-petitions-reconsideration-endangerment-and-cause-or-contribute |archive-date=23 May 2021}}
** {{cite web |ref={{harvid|EPA|2016}} |title=Myths vs. Facts: Denial of Petitions for Reconsideration of the Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act |publisher=U.S. Environmental Protection Agency |date=10 September 2020 |url=https://www.epa.gov/ghgemissions/myths-vs-facts-denial-petitions-reconsideration-endangerment-and-cause-or-contribute |access-date=7 August 2017 |archive-url=https://web.archive.org/web/20210523211147/https://www.epa.gov/ghgemissions/myths-vs-facts-denial-petitions-reconsideration-endangerment-and-cause-or-contribute |archive-date=23 May 2021}}
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** {{cite web |ref={{harvid|EPA|2020}} |url=https://www.epa.gov/ghgemissions/overview-greenhouse-gases |title=Overview of Greenhouse Gases |publisher=U.S. Environmental Protection Agency |date=11 April 2024 |access-date=15 September 2020 |archive-date=October 9, 2024 |archive-url=https://web.archive.org/web/20241009203854/https://www.epa.gov/ghgemissions/overview-greenhouse-gases}}
** {{cite web |ref={{harvid|EPA|2020}} |url=https://www.epa.gov/ghgemissions/overview-greenhouse-gases |title=Overview of Greenhouse Gases |publisher=U.S. Environmental Protection Agency |date=11 April 2024 |access-date=15 September 2020 |archive-date=October 9, 2024 |archive-url=https://web.archive.org/web/20241009203854/https://www.epa.gov/ghgemissions/overview-greenhouse-gases}}
* ''[[EUobserver]]''
* ''[[EUobserver]]''
** {{cite web |ref={{harvid|EUobserver, 20 December|2009}} |date=20 December 2009 |title=Copenhagen failure 'disappointing', 'shameful' |website=euobserver.com |access-date=12 April 2019 |url=https://euobserver.com/environment/29181 |archive-url=https://web.archive.org/web/20190412092312/https://euobserver.com/environment/29181 |archive-date=12 April 2019 |url-status=live}}
** {{cite web |ref={{harvid|EUobserver, 20 December|2009}} |date=20 December 2009 |title=Copenhagen failure 'disappointing', 'shameful' |website=EUobserver |access-date=12 April 2019 |url=https://euobserver.com/environment/29181 |archive-url=https://web.archive.org/web/20190412092312/https://euobserver.com/environment/29181 |archive-date=12 April 2019 |url-status=live}}
* ''[[European Parliament]]''
* ''[[European Parliament]]''
** {{cite web |ref={{harvid|European Parliament, February|2020}} |date=February 2020 |first=M. |last=Ciucci |title=Renewable Energy |website=European Parliament |url=https://www.europarl.europa.eu/factsheets/en/sheet/70/renewable-energy |access-date=3 June 2020}}
** {{cite web |ref={{harvid|European Parliament, February|2020}} |date=February 2020 |first=M. |last=Ciucci |title=Renewable Energy |website=European Parliament |url=https://www.europarl.europa.eu/factsheets/en/sheet/70/renewable-energy |access-date=3 June 2020}}

Latest revision as of 20:40, 27 November 2024

The global map shows sea temperature rises of 0.5 to 1 degree Celsius; land temperature rises of 1 to 2 degrees Celsius; and Arctic temperature rises of up to 4 degrees Celsius.
Changes in surface air temperature over the past 50 years.[1] The Arctic has warmed the most, and temperatures on land have generally increased more than sea surface temperatures.
Earth's average surface air temperature has increased almost 1.5 °C (about 2.5 °F) since the Industrial Revolution. Natural forces cause some variability, but the 20-year average shows the progressive influence of human activity.[2]

Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global temperatures is driven by human activities, especially fossil fuel burning since the Industrial Revolution.[3][4] Fossil fuel use, deforestation, and some agricultural and industrial practices release greenhouse gases.[5] These gases absorb some of the heat that the Earth radiates after it warms from sunlight, warming the lower atmosphere. Carbon dioxide, the primary greenhouse gas driving global warming, has grown by about 50% and is at levels not seen for millions of years.[6]

Climate change has an increasingly large impact on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common.[7] Amplified warming in the Arctic has contributed to thawing permafrost, retreat of glaciers and sea ice decline.[8] Higher temperatures are also causing more intense storms, droughts, and other weather extremes.[9] Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct.[10] Even if efforts to minimize future warming are successful, some effects will continue for centuries. These include ocean heating, ocean acidification and sea level rise.[11]

Climate change threatens people with increased flooding, extreme heat, increased food and water scarcity, more disease, and economic loss. Human migration and conflict can also be a result.[12] The World Health Organization calls climate change one of the biggest threats to global health in the 21st century.[13] Societies and ecosystems will experience more severe risks without action to limit warming.[14] Adapting to climate change through efforts like flood control measures or drought-resistant crops partially reduces climate change risks, although some limits to adaptation have already been reached.[15] Poorer communities are responsible for a small share of global emissions, yet have the least ability to adapt and are most vulnerable to climate change.[16][17]

Bobcat Fire in Monrovia, CA, September 10, 2020
Bleached colony of Acropora coral
A dry lakebed in California, which is experiencing its worst megadrought in 1,200 years.[18]
Examples of some effects of climate change: Wildfire intensified by heat and drought, bleaching of corals occurring more often due to marine heatwaves, and worsening droughts compromising water supplies.

Many climate change impacts have been observed in the first decades of the 21st century, with 2023 the warmest on record at +1.48 °C (2.66 °F) since regular tracking began in 1850.[19][20] Additional warming will increase these impacts and can trigger tipping points, such as melting all of the Greenland ice sheet.[21] Under the 2015 Paris Agreement, nations collectively agreed to keep warming "well under 2 °C". However, with pledges made under the Agreement, global warming would still reach about 2.8 °C (5.0 °F) by the end of the century.[22] Limiting warming to 1.5 °C would require halving emissions by 2030 and achieving net-zero emissions by 2050.[23][24]

Fossil fuel use can be phased out by conserving energy and switching to energy sources that do not produce significant carbon pollution. These energy sources include wind, solar, hydro, and nuclear power.[25] Cleanly generated electricity can replace fossil fuels for powering transportation, heating buildings, and running industrial processes.[26] Carbon can also be removed from the atmosphere, for instance by increasing forest cover and farming with methods that capture carbon in soil.[27]

Terminology

Before the 1980s it was unclear whether the warming effect of increased greenhouse gases was stronger than the cooling effect of airborne particulates in air pollution. Scientists used the term inadvertent climate modification to refer to human impacts on the climate at this time.[28] In the 1980s, the terms global warming and climate change became more common, often being used interchangeably.[29][30][31] Scientifically, global warming refers only to increased surface warming, while climate change describes both global warming and its effects on Earth's climate system, such as precipitation changes.[28]

Climate change can also be used more broadly to include changes to the climate that have happened throughout Earth's history.[32] Global warming—used as early as 1975[33]—became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate.[34] Since the 2000s, climate change has increased usage.[35] Various scientists, politicians and media may use the terms climate crisis or climate emergency to talk about climate change, and may use the term global heating instead of global warming.[36][37]

Global temperature rise

Temperatures prior to present-day global warming

Global surface temperature reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue.[38] Directly observed data is in red.[39]

Over the last few million years the climate cycled through ice ages. One of the hotter periods was the Last Interglacial, around 125,000 years ago, where temperatures were between 0.5 °C and 1.5 °C warmer than before the start of global warming.[40] This period saw sea levels 5 to 10 metres higher than today. The most recent glacial maximum 20,000 years ago was some 5–7 °C colder. This period has sea levels that were over 125 metres (410 ft) lower than today.[41]

Temperatures stabilized in the current interglacial period beginning 11,700 years ago.[42] This period also saw the start of agriculture.[43] Historical patterns of warming and cooling, like the Medieval Warm Period and the Little Ice Age, did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions.[44][45] Climate information for that period comes from climate proxies, such as trees and ice cores.[46][47]

Warming since the Industrial Revolution

In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface.[48]
There has been an increase in ocean heat content during recent decades as the oceans absorb over 90% of the heat from global warming.[49]

Around 1850 thermometer records began to provide global coverage.[50] Between the 18th century and 1970 there was little net warming, as the warming impact of greenhouse gas emissions was offset by cooling from sulfur dioxide emissions. Sulfur dioxide causes acid rain, but it also produces sulfate aerosols in the atmosphere, which reflect sunlight and cause global dimming. After 1970, the increasing accumulation of greenhouse gases and controls on sulfur pollution led to a marked increase in temperature.[51][52][53]

NASA animation portraying global surface temperature changes from 1880 to 2023. The colour blue denotes cooler temperatures and red denotes warmer temperatures.

Ongoing changes in climate have had no precedent for several thousand years.[54] Multiple independent datasets all show worldwide increases in surface temperature,[55] at a rate of around 0.2 °C per decade.[56] The 2014–2023 decade warmed to an average 1.19 °C [1.06–1.30 °C] compared to the pre-industrial baseline (1850–1900).[57] Not every single year was warmer than the last: internal climate variability processes can make any year 0.2 °C warmer or colder than the average.[58] From 1998 to 2013, negative phases of two such processes, Pacific Decadal Oscillation (PDO)[59] and Atlantic Multidecadal Oscillation (AMO)[60] caused a short slower period of warming called the "global warming hiatus".[61] After the "hiatus", the opposite occurred, with years like 2023 exhibiting temperatures well above even the recent average.[62] This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.[63]: 5 [64]

A wide range of other observations reinforce the evidence of warming.[65][66] The upper atmosphere is cooling, because greenhouse gases are trapping heat near the Earth's surface, and so less heat is radiating into space.[67] Warming reduces average snow cover and forces the retreat of glaciers. At the same time, warming also causes greater evaporation from the oceans, leading to more atmospheric humidity, more and heavier precipitation.[68][69] Plants are flowering earlier in spring, and thousands of animal species have been permanently moving to cooler areas.[70]

Differences by region

Different regions of the world warm at different rates. The pattern is independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, the average surface temperature over land regions has increased almost twice as fast as the global average surface temperature.[71] This is because oceans lose more heat by evaporation and oceans can store a lot of heat.[72] The thermal energy in the global climate system has grown with only brief pauses since at least 1970, and over 90% of this extra energy has been stored in the ocean.[73][74] The rest has heated the atmosphere, melted ice, and warmed the continents.[75]

The Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat.[76] Local black carbon deposits on snow and ice also contribute to Arctic warming.[77] Arctic surface temperatures are increasing between three and four times faster than in the rest of the world.[78][79][80] Melting of ice sheets near the poles weakens both the Atlantic and the Antarctic limb of thermohaline circulation, which further changes the distribution of heat and precipitation around the globe.[81][82][83][84]

Future global temperatures

CMIP6 multi-model projections of global surface temperature changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes.[22][85][86]

The World Meteorological Organization estimates there is an 80% chance that global temperatures will exceed 1.5 °C warming for at least one year between 2024 and 2028. The chance of the 5-year average being above 1.5 °C is almost half.[87]

The IPCC expects the 20-year average global temperature to exceed +1.5 °C in the early 2030s.[88] The IPCC Sixth Assessment Report (2021) included projections that by 2100 global warming is very likely to reach 1.0–1.8 °C under a scenario with very low emissions of greenhouse gases, 2.1–3.5 °C under an intermediate emissions scenario, or 3.3–5.7 °C under a very high emissions scenario.[89] The warming will continue past 2100 in the intermediate and high emission scenarios,[90][91] with future projections of global surface temperatures by year 2300 being similar to millions of years ago.[92]

The remaining carbon budget for staying beneath certain temperature increases is determined by modelling the carbon cycle and climate sensitivity to greenhouse gases.[93] According to UNEP, global warming can be kept below 1.5 °C with a 50% chance if emissions after 2023 do not exceed 200 gigatonnes of CO2. This corresponds to around 4 years of current emissions. To stay under 2.0 °C, the carbon budget is 900 gigatonnes of CO2, or 16 years of current emissions.[94]

Causes of recent global temperature rise

Physical drivers of global warming that has happened so far. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented. Whiskers on each bar show the possible error range.

The climate system experiences various cycles on its own which can last for years, decades or even centuries. For example, El Niño events cause short-term spikes in surface temperature while La Niña events cause short term cooling.[95] Their relative frequency can affect global temperature trends on a decadal timescale.[96] Other changes are caused by an imbalance of energy from external forcings.[97] Examples of these include changes in the concentrations of greenhouse gases, solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.[98]

To determine the human contribution to climate change, unique "fingerprints" for all potential causes are developed and compared with both observed patterns and known internal climate variability.[99] For example, solar forcing—whose fingerprint involves warming the entire atmosphere—is ruled out because only the lower atmosphere has warmed.[100] Atmospheric aerosols produce a smaller, cooling effect. Other drivers, such as changes in albedo, are less impactful.[101]

Greenhouse gases

CO2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)

Greenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time.[102]

While water vapour (≈50%) and clouds (≈25%) are the biggest contributors to the greenhouse effect, they primarily change as a function of temperature and are therefore mostly considered to be feedbacks that change climate sensitivity. On the other hand, concentrations of gases such as CO2 (≈20%), tropospheric ozone,[103] CFCs and nitrous oxide are added or removed independently from temperature, and are therefore considered to be external forcings that change global temperatures.[104]

Before the Industrial Revolution, naturally-occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C warmer than it would have been in their absence.[105][106] Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas),[107] has increased the amount of greenhouse gases in the atmosphere. In 2022, the concentrations of CO2 and methane had increased by about 50% and 164%, respectively, since 1750.[108] These CO2 levels are higher than they have been at any time during the last 14 million years.[109] Concentrations of methane are far higher than they were over the last 800,000 years.[110]

The Global Carbon Project shows how additions to CO2 since 1880 have been caused by different sources ramping up one after another.

Global human-caused greenhouse gas emissions in 2019 were equivalent to 59 billion tonnes of CO2. Of these emissions, 75% was CO2, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases.[111] CO2 emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity.[5] Additional CO2 emissions come from deforestation and industrial processes, which include the CO2 released by the chemical reactions for making cement, steel, aluminum, and fertilizer.[112][113][114][115] Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction.[116][117] Nitrous oxide emissions largely come from the microbial decomposition of fertilizer.[118][119]

While methane only lasts in the atmosphere for an average of 12 years,[120] CO2 lasts much longer. The Earth's surface absorbs CO2 as part of the carbon cycle. While plants on land and in the ocean absorb most excess emissions of CO2 every year, that CO2 is returned to the atmosphere when biological matter is digested, burns, or decays.[121] Land-surface carbon sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global CO2 emissions.[122] The ocean has absorbed 20 to 30% of emitted CO2 over the last two decades.[123] CO2 is only removed from the atmosphere for the long term when it is stored in the Earth's crust, which is a process that can take millions of years to complete.[121]

Land surface changes

The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy.[124]

Around 30% of Earth's land area is largely unusable for humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland and 34% is agricultural land.[125] Deforestation is the main land use change contributor to global warming,[126] as the destroyed trees release CO2, and are not replaced by new trees, removing that carbon sink.[127] Between 2001 and 2018, 27% of deforestation was from permanent clearing to enable agricultural expansion for crops and livestock. Another 24% has been lost to temporary clearing under the shifting cultivation agricultural systems. 26% was due to logging for wood and derived products, and wildfires have accounted for the remaining 23%.[128] Some forests have not been fully cleared, but were already degraded by these impacts. Restoring these forests also recovers their potential as a carbon sink.[129]

Local vegetation cover impacts how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also modify the release of chemical compounds that influence clouds, and by changing wind patterns.[130] In tropic and temperate areas the net effect is to produce significant warming, and forest restoration can make local temperatures cooler.[129] At latitudes closer to the poles, there is a cooling effect as forest is replaced by snow-covered (and more reflective) plains.[130] Globally, these increases in surface albedo have been the dominant direct influence on temperature from land use change. Thus, land use change to date is estimated to have a slight cooling effect.[131]

Other factors

Aerosols and clouds

Air pollution, in the form of aerosols, affects the climate on a large scale.[132] Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed. This phenomenon is popularly known as global dimming,[133] and is primarily attributed to sulfate aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like coal and bunker fuel.[53] Smaller contributions come from black carbon (from combustion of fossil fuels and biomass), and from dust.[134][135][136] Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.[137][53]

Aerosols also have indirect effects on the Earth's energy budget. Sulfate aerosols act as cloud condensation nuclei and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets.[138] They also reduce the growth of raindrops, which makes clouds more reflective to incoming sunlight.[139] Indirect effects of aerosols are the largest uncertainty in radiative forcing.[140]

While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise.[141] Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050.[142] The effect of decreasing sulfur content of fuel oil for ships since 2020[143] is estimated to cause an additional 0.05 °C increase in global mean temperature by 2050.[144]

Solar and volcanic activity

The Fourth National Climate Assessment ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming.[145][146]

As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system.[140] Solar irradiance has been measured directly by satellites,[147] and indirect measurements are available from the early 1600s onwards.[140] Since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the troposphere).[148] The upper atmosphere (the stratosphere) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.[100] This is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.[149]

Explosive volcanic eruptions can release gases, dust and ash that partially block sunlight and reduce temperatures, or they can send water vapour into the atmosphere, which adds to greenhouse gases and increases temperatures.[150] These impacts on temperature only last for several years, because both water vapour and volcanic material have low persistence in the atmosphere.[151] volcanic CO2 emissions are more persistent, but they are equivalent to less than 1% of current human-caused CO2 emissions.[152] Volcanic activity still represents the single largest natural impact (forcing) on temperature in the industrial era. Yet, like the other natural forcings, it has had negligible impacts on global temperature trends since the Industrial Revolution.[151]

Climate change feedbacks

Sea ice reflects 50% to 70% of incoming sunlight, while the ocean, being darker, reflects only 6%. As an area of sea ice melts and exposes more ocean, more heat is absorbed by the ocean, raising temperatures that melt still more ice. This is a positive feedback process.[153]

The climate system's response to an initial forcing is shaped by feedbacks, which either amplify or dampen the change. Self-reinforcing or positive feedbacks increase the response, while balancing or negative feedbacks reduce it.[154] The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and the net effect of clouds.[155][156] The primary balancing mechanism is radiative cooling, as Earth's surface gives off more heat to space in response to rising temperature.[157] In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of CO2 on plant growth.[158] Feedbacks are expected to trend in a positive direction as greenhouse gas emissions continue, raising climate sensitivity.[159]

These feedback processes alter the pace of global warming. For instance, warmer air can hold more moisture in the form of water vapour, which is itself a potent greenhouse gas.[155] Warmer air can also make clouds higher and thinner, and therefore more insulating, increasing climate warming.[160] The reduction of snow cover and sea ice in the Arctic is another major feedback, this reduces the reflectivity of the Earth's surface in the region and accelerates Arctic warming.[161][162] This additional warming also contributes to permafrost thawing, which releases methane and CO2 into the atmosphere.[163]

Around half of human-caused CO2 emissions have been absorbed by land plants and by the oceans.[164] This fraction is not static and if future CO2 emissions decrease, the Earth will be able to absorb up to around 70%. If they increase substantially, it'll still absorb more carbon than now, but the overall fraction will decrease to below 40%.[165] This is because climate change increases droughts and heat waves that eventually inhibit plant growth on land, and soils will release more carbon from dead plants when they are warmer.[166][167] The rate at which oceans absorb atmospheric carbon will be lowered as they become more acidic and experience changes in thermohaline circulation and phytoplankton distribution.[168][169][82] Uncertainty over feedbacks, particularly cloud cover,[170] is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.[171]

Modelling

Energy flows between space, the atmosphere, and Earth's surface. Most sunlight passes through the atmosphere to heat the Earth's surface, then greenhouse gases absorb most of the heat the Earth radiates in response. Adding to greenhouse gases increases this insulating effect, causing an energy imbalance that heats the planet up.

A climate model is a representation of the physical, chemical and biological processes that affect the climate system.[172] Models include natural processes like changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing.[173] Models are used to estimate the degree of warming future emissions will cause when accounting for the strength of climate feedbacks.[174][175] Models also predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere.[176]

The physical realism of models is tested by examining their ability to simulate current or past climates.[177] Past models have underestimated the rate of Arctic shrinkage[178] and underestimated the rate of precipitation increase.[179] Sea level rise since 1990 was underestimated in older models, but more recent models agree well with observations.[180] The 2017 United States-published National Climate Assessment notes that "climate models may still be underestimating or missing relevant feedback processes".[181] Additionally, climate models may be unable to adequately predict short-term regional climatic shifts.[182]

A subset of climate models add societal factors to a physical climate model. These models simulate how population, economic growth, and energy use affect—and interact with—the physical climate. With this information, these models can produce scenarios of future greenhouse gas emissions. This is then used as input for physical climate models and carbon cycle models to predict how atmospheric concentrations of greenhouse gases might change.[183][184] Depending on the socioeconomic scenario and the mitigation scenario, models produce atmospheric CO2 concentrations that range widely between 380 and 1400 ppm.[185]

Impacts

The sixth IPCC Assessment Report projects changes in average soil moisture at 2.0 °C of warming, as measured in standard deviations from the 1850 to 1900 baseline.

Environmental effects

The environmental effects of climate change are broad and far-reaching, affecting oceans, ice, and weather. Changes may occur gradually or rapidly. Evidence for these effects comes from studying climate change in the past, from modelling, and from modern observations.[186] Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency.[187] Extremely wet or dry events within the monsoon period have increased in India and East Asia.[188] Monsoonal precipitation over the Northern Hemisphere has increased since 1980.[189] The rainfall rate and intensity of hurricanes and typhoons is likely increasing,[190] and the geographic range likely expanding poleward in response to climate warming.[191] Frequency of tropical cyclones has not increased as a result of climate change.[192]

Historical sea level reconstruction and projections up to 2100 published in 2017 by the U.S. Global Change Research Program[193]

Global sea level is rising as a consequence of thermal expansion and the melting of glaciers and ice sheets. Sea level rise has increased over time, reaching 4.8 cm per decade between 2014 and 2023.[194] Over the 21st century, the IPCC projects 32–62 cm of sea level rise under a low emission scenario, 44–76 cm under an intermediate one and 65–101 cm under a very high emission scenario.[195] Marine ice sheet instability processes in Antarctica may add substantially to these values,[196] including the possibility of a 2-meter sea level rise by 2100 under high emissions.[197]

Climate change has led to decades of shrinking and thinning of the Arctic sea ice.[198] While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2 °C.[199] Higher atmospheric CO2 concentrations cause more CO2 to dissolve in the oceans, which is making them more acidic.[200] Because oxygen is less soluble in warmer water,[201] its concentrations in the ocean are decreasing, and dead zones are expanding.[202]

Tipping points and long-term impacts

Different levels of global warming may cause different parts of Earth's climate system to reach tipping points that cause transitions to different states.[203][204]

Greater degrees of global warming increase the risk of passing through 'tipping points'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state.[205][206] For instance, the Greenland ice sheet is already melting, but if global warming reaches levels between 1.7 °C and 2.3 °C, its melting will continue until it fully disappears. If the warming is later reduced to 1.5 °C or less, it will still lose a lot more ice than if the warming was never allowed to reach the threshold in the first place.[207] While the ice sheets would melt over millennia, other tipping points would occur faster and give societies less time to respond. The collapse of major ocean currents like the Atlantic meridional overturning circulation (AMOC), and irreversible damage to key ecosystems like the Amazon rainforest and coral reefs can unfold in a matter of decades.[204]

The long-term effects of climate change on oceans include further ice melt, ocean warming, sea level rise, ocean acidification and ocean deoxygenation.[208] The timescale of long-term impacts are centuries to millennia due to CO2's long atmospheric lifetime.[209] The result is an estimated total sea level rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years.[210] Oceanic CO2 uptake is slow enough that ocean acidification will also continue for hundreds to thousands of years.[211] Deep oceans (below 2,000 metres (6,600 ft)) are also already committed to losing over 10% of their dissolved oxygen by the warming which occurred to date.[212] Further, the West Antarctic ice sheet appears committed to practically irreversible melting, which would increase the sea levels by at least 3.3 m (10 ft 10 in) over approximately 2000 years.[204][213][214]

Nature and wildlife

Recent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes.[215] For instance, the range of hundreds of North American birds has shifted northward at an average rate of 1.5 km/year over the past 55 years.[216] Higher atmospheric CO2 levels and an extended growing season have resulted in global greening. However, heatwaves and drought have reduced ecosystem productivity in some regions. The future balance of these opposing effects is unclear.[217] A related phenomenon driven by climate change is woody plant encroachment, affecting up to 500 million hectares globally.[218] Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics.[219] The size and speed of global warming is making abrupt changes in ecosystems more likely.[220] Overall, it is expected that climate change will result in the extinction of many species.[221]

The oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land.[222] Just as on land, heat waves in the ocean occur more frequently due to climate change, harming a wide range of organisms such as corals, kelp, and seabirds.[223] Ocean acidification makes it harder for marine calcifying organisms such as mussels, barnacles and corals to produce shells and skeletons; and heatwaves have bleached coral reefs.[224] Harmful algal blooms enhanced by climate change and eutrophication lower oxygen levels, disrupt food webs and cause great loss of marine life.[225] Coastal ecosystems are under particular stress. Almost half of global wetlands have disappeared due to climate change and other human impacts.[226] Plants have come under increased stress from damage by insects.[227]

Climate change impacts on the environment

Humans

Extreme weather will be progressively more common as the Earth warms.[232]

The effects of climate change are impacting humans everywhere in the world.[233] Impacts can be observed on all continents and ocean regions,[234] with low-latitude, less developed areas facing the greatest risk.[235] Continued warming has potentially "severe, pervasive and irreversible impacts" for people and ecosystems.[236] The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries.[237]

Health and food

The World Health Organization calls climate change one of the biggest threats to global health in the 21st century.[13] Scientists have warned about the irreversible harms it poses.[238] Extreme weather events affect public health, and food and water security.[239][240][241] Temperature extremes lead to increased illness and death.[239][240] Climate change increases the intensity and frequency of extreme weather events.[240][241] It can affect transmission of infectious diseases, such as dengue fever and malaria.[238][239] According to the World Economic Forum, 14.5 million more deaths are expected due to climate change by 2050.[242] 30% of the global population currently live in areas where extreme heat and humidity are already associated with excess deaths.[243][244] By 2100, 50% to 75% of the global population would live in such areas.[243][245]

While total crop yields have been increasing in the past 50 years due to agricultural improvements, climate change has already decreased the rate of yield growth.[241] Fisheries have been negatively affected in multiple regions.[241] While agricultural productivity has been positively affected in some high latitude areas, mid- and low-latitude areas have been negatively affected.[241] According to the World Economic Forum, an increase in drought in certain regions could cause 3.2 million deaths from malnutrition by 2050 and stunting in children.[246] With 2 °C warming, global livestock headcounts could decline by 7–10% by 2050, as less animal feed will be available.[247] If the emissions continue to increase for the rest of century, then over 9 million climate-related deaths would occur annually by 2100.[248]

Livelihoods and inequality

Economic damages due to climate change may be severe and there is a chance of disastrous consequences.[249] Severe impacts are expected in South-East Asia and sub-Saharan Africa, where most of the local inhabitants are dependent upon natural and agricultural resources.[250][251] Heat stress can prevent outdoor labourers from working. If warming reaches 4 °C then labour capacity in those regions could be reduced by 30 to 50%.[252] The World Bank estimates that between 2016 and 2030, climate change could drive over 120 million people into extreme poverty without adaptation.[253]

Inequalities based on wealth and social status have worsened due to climate change.[254] Major difficulties in mitigating, adapting to, and recovering from climate shocks are faced by marginalized people who have less control over resources.[255][250] Indigenous people, who are subsistent on their land and ecosystems, will face endangerment to their wellness and lifestyles due to climate change.[256] An expert elicitation concluded that the role of climate change in armed conflict has been small compared to factors such as socio-economic inequality and state capabilities.[257]

While women are not inherently more at risk from climate change and shocks, limits on women's resources and discriminatory gender norms constrain their adaptive capacity and resilience.[258] For example, women's work burdens, including hours worked in agriculture, tend to decline less than men's during climate shocks such as heat stress.[258]

Climate migration

Low-lying islands and coastal communities are threatened by sea level rise, which makes urban flooding more common. Sometimes, land is permanently lost to the sea.[259] This could lead to statelessness for people in island nations, such as the Maldives and Tuvalu.[260] In some regions, the rise in temperature and humidity may be too severe for humans to adapt to.[261] With worst-case climate change, models project that almost one-third of humanity might live in Sahara-like uninhabitable and extremely hot climates.[262]

These factors can drive climate or environmental migration, within and between countries.[263] More people are expected to be displaced because of sea level rise, extreme weather and conflict from increased competition over natural resources. Climate change may also increase vulnerability, leading to "trapped populations" who are not able to move due to a lack of resources.[264]

Climate change impacts on people

Reducing and recapturing emissions

Global greenhouse gas emission scenarios, based on policies and pledges as of November 2021

Climate change can be mitigated by reducing the rate at which greenhouse gases are emitted into the atmosphere, and by increasing the rate at which carbon dioxide is removed from the atmosphere.[270] To limit global warming to less than 1.5 °C global greenhouse gas emissions needs to be net-zero by 2050, or by 2070 with a 2 °C target.[271] This requires far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry.[272]

The United Nations Environment Programme estimates that countries need to triple their pledges under the Paris Agreement within the next decade to limit global warming to 2 °C. An even greater level of reduction is required to meet the 1.5 °C goal.[273] With pledges made under the Paris Agreement as of 2024, there would be a 66% chance that global warming is kept under 2.8 °C by the end of the century (range: 1.9–3.7 °C, depending on exact implementation and technological progress). When only considering current policies, this raises to 3.1 °C.[274] Globally, limiting warming to 2 °C may result in higher economic benefits than economic costs.[275]

Although there is no single pathway to limit global warming to 1.5 or 2 °C,[276] most scenarios and strategies see a major increase in the use of renewable energy in combination with increased energy efficiency measures to generate the needed greenhouse gas reductions.[277] To reduce pressures on ecosystems and enhance their carbon sequestration capabilities, changes would also be necessary in agriculture and forestry,[278] such as preventing deforestation and restoring natural ecosystems by reforestation.[279]

Other approaches to mitigating climate change have a higher level of risk. Scenarios that limit global warming to 1.5 °C typically project the large-scale use of carbon dioxide removal methods over the 21st century.[280] There are concerns, though, about over-reliance on these technologies, and environmental impacts.[281] Solar radiation modification (SRM) is also a possible supplement to deep reductions in emissions. However, SRM raises significant ethical and legal concerns, and the risks are imperfectly understood.[282]

Clean energy

Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing.[283]
Wind and solar power, Germany

Renewable energy is key to limiting climate change.[284] For decades, fossil fuels have accounted for roughly 80% of the world's energy use.[285] The remaining share has been split between nuclear power and renewables (including hydropower, bioenergy, wind and solar power and geothermal energy).[286] Fossil fuel use is expected to peak in absolute terms prior to 2030 and then to decline, with coal use experiencing the sharpest reductions.[287] Renewables represented 86% of all new electricity generation installed in 2023.[288] Other forms of clean energy, such as nuclear and hydropower, currently have a larger share of the energy supply. However, their future growth forecasts appear limited in comparison.[289]

While solar panels and onshore wind are now among the cheapest forms of adding new power generation capacity in many locations,[290] green energy policies are needed to achieve a rapid transition from fossil fuels to renewables.[291] To achieve carbon neutrality by 2050, renewable energy would become the dominant form of electricity generation, rising to 85% or more by 2050 in some scenarios. Investment in coal would be eliminated and coal use nearly phased out by 2050.[292][293]

Electricity generated from renewable sources would also need to become the main energy source for heating and transport.[294] Transport can switch away from internal combustion engine vehicles and towards electric vehicles, public transit, and active transport (cycling and walking).[295][296] For shipping and flying, low-carbon fuels would reduce emissions.[295] Heating could be increasingly decarbonized with technologies like heat pumps.[297]

There are obstacles to the continued rapid growth of clean energy, including renewables.[298] Wind and solar produce energy intermittently and with seasonal variability. Traditionally, hydro dams with reservoirs and fossil fuel power plants have been used when variable energy production is low. Going forward, battery storage can be expanded, energy demand and supply can be matched, and long-distance transmission can smooth variability of renewable outputs.[284] Bioenergy is often not carbon-neutral and may have negative consequences for food security.[299] The growth of nuclear power is constrained by controversy around radioactive waste, nuclear weapon proliferation, and accidents.[300][301] Hydropower growth is limited by the fact that the best sites have been developed, and new projects are confronting increased social and environmental concerns.[302]

Low-carbon energy improves human health by minimizing climate change as well as reducing air pollution deaths,[303] which were estimated at 7 million annually in 2016.[304] Meeting the Paris Agreement goals that limit warming to a 2 °C increase could save about a million of those lives per year by 2050, whereas limiting global warming to 1.5 °C could save millions and simultaneously increase energy security and reduce poverty.[305] Improving air quality also has economic benefits which may be larger than mitigation costs.[306]

Energy conservation

Reducing energy demand is another major aspect of reducing emissions.[307] If less energy is needed, there is more flexibility for clean energy development. It also makes it easier to manage the electricity grid, and minimizes carbon-intensive infrastructure development.[308] Major increases in energy efficiency investment will be required to achieve climate goals, comparable to the level of investment in renewable energy.[309] Several COVID-19 related changes in energy use patterns, energy efficiency investments, and funding have made forecasts for this decade more difficult and uncertain.[310]

Strategies to reduce energy demand vary by sector. In the transport sector, passengers and freight can switch to more efficient travel modes, such as buses and trains, or use electric vehicles.[311] Industrial strategies to reduce energy demand include improving heating systems and motors, designing less energy-intensive products, and increasing product lifetimes.[312] In the building sector the focus is on better design of new buildings, and higher levels of energy efficiency in retrofitting.[313] The use of technologies like heat pumps can also increase building energy efficiency.[314]

Agriculture and industry

Taking into account direct and indirect emissions, industry is the sector with the highest share of global emissions. Data as of 2019 from the IPCC.

Agriculture and forestry face a triple challenge of limiting greenhouse gas emissions, preventing the further conversion of forests to agricultural land, and meeting increases in world food demand.[315] A set of actions could reduce agriculture and forestry-based emissions by two-thirds from 2010 levels. These include reducing growth in demand for food and other agricultural products, increasing land productivity, protecting and restoring forests, and reducing greenhouse gas emissions from agricultural production.[316]

On the demand side, a key component of reducing emissions is shifting people towards plant-based diets.[317] Eliminating the production of livestock for meat and dairy would eliminate about 3/4ths of all emissions from agriculture and other land use.[318] Livestock also occupy 37% of ice-free land area on Earth and consume feed from the 12% of land area used for crops, driving deforestation and land degradation.[319]

Steel and cement production are responsible for about 13% of industrial CO2 emissions. In these industries, carbon-intensive materials such as coke and lime play an integral role in the production, so that reducing CO2 emissions requires research into alternative chemistries.[320] Where energy production or CO2-intensive heavy industries continue to produce waste CO2, technology can sometimes be used to capture and store most of the gas instead of releasing it to the atmosphere.[321] This technology, carbon capture and storage (CCS), could have a critical but limited role in reducing emissions.[321] It is relatively expensive[322] and has been deployed only to an extent that removes around 0.1% of annual greenhouse gas emissions.[321]

Carbon dioxide removal

Most CO2 emissions have been absorbed by carbon sinks, including plant growth, soil uptake, and ocean uptake (2020 Global Carbon Budget).

Natural carbon sinks can be enhanced to sequester significantly larger amounts of CO2 beyond naturally occurring levels.[323] Reforestation and afforestation (planting forests where there were none before) are among the most mature sequestration techniques, although the latter raises food security concerns.[324] Farmers can promote sequestration of carbon in soils through practices such as use of winter cover crops, reducing the intensity and frequency of tillage, and using compost and manure as soil amendments.[325] Forest and landscape restoration yields many benefits for the climate, including greenhouse gas emissions sequestration and reduction.[129] Restoration/recreation of coastal wetlands, prairie plots and seagrass meadows increases the uptake of carbon into organic matter.[326][327] When carbon is sequestered in soils and in organic matter such as trees, there is a risk of the carbon being re-released into the atmosphere later through changes in land use, fire, or other changes in ecosystems.[328]

The use of bioenergy in conjunction with carbon capture and storage (BECCS) can result in net negative emissions as CO2 is drawn from the atmosphere.[329] It remains highly uncertain whether carbon dioxide removal techniques will be able to play a large role in limiting warming to 1.5 °C. Policy decisions that rely on carbon dioxide removal increase the risk of global warming rising beyond international goals.[330]

Adaptation

Adaptation is "the process of adjustment to current or expected changes in climate and its effects".[331]: 5  Without additional mitigation, adaptation cannot avert the risk of "severe, widespread and irreversible" impacts.[332] More severe climate change requires more transformative adaptation, which can be prohibitively expensive.[333] The capacity and potential for humans to adapt is unevenly distributed across different regions and populations, and developing countries generally have less.[334] The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic sanitation and electricity, but progress is slow. Many countries have implemented adaptation policies. However, there is a considerable gap between necessary and available finance.[335]

Adaptation to sea level rise consists of avoiding at-risk areas, learning to live with increased flooding, and building flood controls. If that fails, managed retreat may be needed.[336] There are economic barriers for tackling dangerous heat impact. Avoiding strenuous work or having air conditioning is not possible for everybody.[337] In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control, and genetic improvements for increased tolerance to a changing climate.[338] Insurance allows for risk-sharing, but is often difficult to get for people on lower incomes.[339] Education, migration and early warning systems can reduce climate vulnerability.[340] Planting mangroves or encouraging other coastal vegetation can buffer storms.[341][342]

Ecosystems adapt to climate change, a process that can be supported by human intervention. By increasing connectivity between ecosystems, species can migrate to more favourable climate conditions. Species can also be introduced to areas acquiring a favourable climate. Protection and restoration of natural and semi-natural areas helps build resilience, making it easier for ecosystems to adapt. Many of the actions that promote adaptation in ecosystems, also help humans adapt via ecosystem-based adaptation. For instance, restoration of natural fire regimes makes catastrophic fires less likely, and reduces human exposure. Giving rivers more space allows for more water storage in the natural system, reducing flood risk. Restored forest acts as a carbon sink, but planting trees in unsuitable regions can exacerbate climate impacts.[343]

There are synergies but also trade-offs between adaptation and mitigation.[344] An example for synergy is increased food productivity, which has large benefits for both adaptation and mitigation.[345] An example of a trade-off is that increased use of air conditioning allows people to better cope with heat, but increases energy demand. Another trade-off example is that more compact urban development may reduce emissions from transport and construction, but may also increase the urban heat island effect, exposing people to heat-related health risks.[346]

Examples of adaptation methods

Policies and politics

The Climate Change Performance Index ranks countries by greenhouse gas emissions (40% of score), renewable energy (20%), energy use (20%), and climate policy (20%).
  High
  Medium
  Low
  Very low

Countries that are most vulnerable to climate change have typically been responsible for a small share of global emissions. This raises questions about justice and fairness.[347] Limiting global warming makes it much easier to achieve the UN's Sustainable Development Goals, such as eradicating poverty and reducing inequalities. The connection is recognized in Sustainable Development Goal 13 which is to "take urgent action to combat climate change and its impacts".[348] The goals on food, clean water and ecosystem protection have synergies with climate mitigation.[349]

The geopolitics of climate change is complex. It has often been framed as a free-rider problem, in which all countries benefit from mitigation done by other countries, but individual countries would lose from switching to a low-carbon economy themselves. Sometimes mitigation also has localized benefits though. For instance, the benefits of a coal phase-out to public health and local environments exceed the costs in almost all regions.[350] Furthermore, net importers of fossil fuels win economically from switching to clean energy, causing net exporters to face stranded assets: fossil fuels they cannot sell.[351]

Policy options

A wide range of policies, regulations, and laws are being used to reduce emissions. As of 2019, carbon pricing covers about 20% of global greenhouse gas emissions.[352] Carbon can be priced with carbon taxes and emissions trading systems.[353] Direct global fossil fuel subsidies reached $319 billion in 2017, and $5.2 trillion when indirect costs such as air pollution are priced in.[354] Ending these can cause a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths.[355] Money saved on fossil subsidies could be used to support the transition to clean energy instead.[356] More direct methods to reduce greenhouse gases include vehicle efficiency standards, renewable fuel standards, and air pollution regulations on heavy industry.[357] Several countries require utilities to increase the share of renewables in power production.[358]

Climate justice

Policy designed through the lens of climate justice tries to address human rights issues and social inequality. According to proponents of climate justice, the costs of climate adaptation should be paid by those most responsible for climate change, while the beneficiaries of payments should be those suffering impacts. One way this can be addressed in practice is to have wealthy nations pay poorer countries to adapt.[359]

Oxfam found that in 2023 the wealthiest 10% of people were responsible for 50% of global emissions, while the bottom 50% were responsible for just 8%.[360] Production of emissions is another way to look at responsibility: under that approach, the top 21 fossil fuel companies would owe cumulative climate reparations of $5.4 trillion over the period 2025–2050.[361] To achieve a just transition, people working in the fossil fuel sector would also need other jobs, and their communities would need investments.[362]

International climate agreements

Since 2000, rising CO2 emissions in China and the rest of world have surpassed the output of the United States and Europe.[363]
Per person, the United States generates CO2 at a far faster rate than other primary regions.[363]

Nearly all countries in the world are parties to the 1994 United Nations Framework Convention on Climate Change (UNFCCC).[364] The goal of the UNFCCC is to prevent dangerous human interference with the climate system.[365] As stated in the convention, this requires that greenhouse gas concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can be sustained.[366] The UNFCCC does not itself restrict emissions but rather provides a framework for protocols that do. Global emissions have risen since the UNFCCC was signed.[367] Its yearly conferences are the stage of global negotiations.[368]

The 1997 Kyoto Protocol extended the UNFCCC and included legally binding commitments for most developed countries to limit their emissions.[369] During the negotiations, the G77 (representing developing countries) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions,[370] since developed countries contributed most to the accumulation of greenhouse gases in the atmosphere. Per-capita emissions were also still relatively low in developing countries and developing countries would need to emit more to meet their development needs.[371]

The 2009 Copenhagen Accord has been widely portrayed as disappointing because of its low goals, and was rejected by poorer nations including the G77.[372] Associated parties aimed to limit the global temperature rise to below 2 °C.[373] The Accord set the goal of sending $100 billion per year to developing countries for mitigation and adaptation by 2020, and proposed the founding of the Green Climate Fund.[374] As of 2020, only 83.3 billion were delivered. Only in 2023 the target is expected to be achieved.[375]

In 2015 all UN countries negotiated the Paris Agreement, which aims to keep global warming well below 2.0 °C and contains an aspirational goal of keeping warming under 1.5 °C.[376] The agreement replaced the Kyoto Protocol. Unlike Kyoto, no binding emission targets were set in the Paris Agreement. Instead, a set of procedures was made binding. Countries have to regularly set ever more ambitious goals and reevaluate these goals every five years.[377] The Paris Agreement restated that developing countries must be financially supported.[378] As of October 2021, 194 states and the European Union have signed the treaty and 191 states and the EU have ratified or acceded to the agreement.[379]

The 1987 Montreal Protocol, an international agreement to phase out production of ozone-depleting gases, has had benefits for climate change mitigation.[380] Several ozone-depleting gases like chlorofluorocarbons are powerful greenhouse gases, so banning their production and usage may have avoided a temperature rise of 0.5 °C–1.0 °C,[381] as well as additional warming by preventing damage to vegetation from ultraviolet radiation.[382] It is estimated that the agreement has been more effective at curbing greenhouse gas emissions than the Kyoto Protocol specifically designed to do so.[383] The most recent amendment to the Montreal Protocol, the 2016 Kigali Amendment, committed to reducing the emissions of hydrofluorocarbons, which served as a replacement for banned ozone-depleting gases and are also potent greenhouse gases.[384] Should countries comply with the amendment, a warming of 0.3 °C–0.5 °C is estimated to be avoided.[385]

National responses

Annual CO2 emissions by region. This measures fossil fuel and industry emissions. Land use change is not included.[386]

In 2019, the United Kingdom parliament became the first national government to declare a climate emergency.[387] Other countries and jurisdictions followed suit.[388] That same year, the European Parliament declared a "climate and environmental emergency".[389] The European Commission presented its European Green Deal with the goal of making the EU carbon-neutral by 2050.[390] In 2021, the European Commission released its "Fit for 55" legislation package, which contains guidelines for the car industry; all new cars on the European market must be zero-emission vehicles from 2035.[391]

Major countries in Asia have made similar pledges: South Korea and Japan have committed to become carbon-neutral by 2050, and China by 2060.[392] While India has strong incentives for renewables, it also plans a significant expansion of coal in the country.[393] Vietnam is among very few coal-dependent, fast-developing countries that pledged to phase out unabated coal power by the 2040s or as soon as possible thereafter.[394]

As of 2021, based on information from 48 national climate plans, which represent 40% of the parties to the Paris Agreement, estimated total greenhouse gas emissions will be 0.5% lower compared to 2010 levels, below the 45% or 25% reduction goals to limit global warming to 1.5 °C or 2 °C, respectively.[395]

Society

Denial and misinformation

Data has been cherry picked from short periods to falsely assert that global temperatures are not rising. Blue trendlines show short periods that mask longer-term warming trends (red trendlines). Blue rectangle with blue dots shows the so-called global warming hiatus.[396]

Public debate about climate change has been strongly affected by climate change denial and misinformation, which originated in the United States and has since spread to other countries, particularly Canada and Australia. Climate change denial has originated from fossil fuel companies, industry groups, conservative think tanks, and contrarian scientists.[397] Like the tobacco industry, the main strategy of these groups has been to manufacture doubt about climate-change related scientific data and results.[398] People who hold unwarranted doubt about climate change are called climate change "skeptics", although "contrarians" or "deniers" are more appropriate terms.[399]

There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimize the negative impacts of climate change.[400] Manufacturing uncertainty about the science later developed into a manufactured controversy: creating the belief that there is significant uncertainty about climate change within the scientific community to delay policy changes.[401] Strategies to promote these ideas include criticism of scientific institutions,[402] and questioning the motives of individual scientists.[400] An echo chamber of climate-denying blogs and media has further fomented misunderstanding of climate change.[403]

Public awareness and opinion

The public substantially underestimates the degree of scientific consensus that humans are causing climate change.[404] Studies from 2019 to 2021[405][4][406] found scientific consensus to range from 98.7 to 100%.

Climate change came to international public attention in the late 1980s.[407] Due to media coverage in the early 1990s, people often confused climate change with other environmental issues like ozone depletion.[408] In popular culture, the climate fiction movie The Day After Tomorrow (2004) and the Al Gore documentary An Inconvenient Truth (2006) focused on climate change.[407]

Significant regional, gender, age and political differences exist in both public concern for, and understanding of, climate change. More highly educated people, and in some countries, women and younger people, were more likely to see climate change as a serious threat.[409] College biology textbooks from the 2010s featured less content on climate change compared to those from the preceding decade, with decreasing emphasis on solutions.[410] Partisan gaps also exist in many countries,[411] and countries with high CO2 emissions tend to be less concerned.[412] Views on causes of climate change vary widely between countries.[413] Concern has increased over time,[414] and a majority of citizens in many countries now express a high level of worry about climate change, or view it as a global emergency.[415] Higher levels of worry are associated with stronger public support for policies that address climate change.[416]

Climate movement

Climate protests demand that political leaders take action to prevent climate change. They can take the form of public demonstrations, fossil fuel divestment, lawsuits and other activities.[417] Prominent demonstrations include the School Strike for Climate. In this initiative, young people across the globe have been protesting since 2018 by skipping school on Fridays, inspired by Swedish teenager Greta Thunberg.[418] Mass civil disobedience actions by groups like Extinction Rebellion have protested by disrupting roads and public transport.[419]

Litigation is increasingly used as a tool to strengthen climate action from public institutions and companies. Activists also initiate lawsuits which target governments and demand that they take ambitious action or enforce existing laws on climate change.[420] Lawsuits against fossil-fuel companies generally seek compensation for loss and damage.[421]

History

Early discoveries

This 1912 article succinctly describes the greenhouse effect, how burning coal creates carbon dioxide to cause global warming and climate change.[422]

Scientists in the 19th century such as Alexander von Humboldt began to foresee the effects of climate change.[423][424][425][426] In the 1820s, Joseph Fourier proposed the greenhouse effect to explain why Earth's temperature was higher than the Sun's energy alone could explain. Earth's atmosphere is transparent to sunlight, so sunlight reaches the surface where it is converted to heat. However, the atmosphere is not transparent to heat radiating from the surface, and captures some of that heat, which in turn warms the planet.[427]

In 1856 Eunice Newton Foote demonstrated that the warming effect of the Sun is greater for air with water vapour than for dry air, and that the effect is even greater with carbon dioxide (CO2). She concluded that "An atmosphere of that gas would give to our earth a high temperature..."[428][429]

Studying what would become known as the greenhouse effect, Tyndall's pre-1861 ratio spectrophotometer measured how much various gases in a tube absorb and emit infrared radiation—which humans experience as heat.

Starting in 1859,[430] John Tyndall established that nitrogen and oxygen—together totalling 99% of dry air—are transparent to radiated heat. However, water vapour and gases such as methane and carbon dioxide absorb radiated heat and re-radiate that heat into the atmosphere. Tyndall proposed that changes in the concentrations of these gases may have caused climatic changes in the past, including ice ages.[431]

Svante Arrhenius noted that water vapour in air continuously varied, but the CO2 concentration in air was influenced by long-term geological processes. Warming from increased CO2 levels would increase the amount of water vapour, amplifying warming in a positive feedback loop. In 1896, he published the first climate model of its kind, projecting that halving CO2 levels could have produced a drop in temperature initiating an ice age. Arrhenius calculated the temperature increase expected from doubling CO2 to be around 5–6 °C.[432] Other scientists were initially sceptical and believed that the greenhouse effect was saturated so that adding more CO2 would make no difference, and that the climate would be self-regulating.[433] Beginning in 1938, Guy Stewart Callendar published evidence that climate was warming and CO2 levels were rising,[434] but his calculations met the same objections.[433]

Development of a scientific consensus

Scientific consensus on causation: Academic studies of scientific agreement on human-caused global warming among climate experts (2010–2015) reflect that the level of consensus correlates with expertise in climate science.[435] A 2019 study found scientific consensus to be at 100%,[436] and a 2021 study concluded that consensus exceeded 99%.[437] Another 2021 study found that 98.7% of climate experts indicated that the Earth is getting warmer mostly because of human activity.[438]

In the 1950s, Gilbert Plass created a detailed computer model that included different atmospheric layers and the infrared spectrum. This model predicted that increasing CO2 levels would cause warming. Around the same time, Hans Suess found evidence that CO2 levels had been rising, and Roger Revelle showed that the oceans would not absorb the increase. The two scientists subsequently helped Charles Keeling to begin a record of continued increase, which has been termed the "Keeling Curve".[433] Scientists alerted the public,[439] and the dangers were highlighted at James Hansen's 1988 Congressional testimony.[34] The Intergovernmental Panel on Climate Change (IPCC), set up in 1988 to provide formal advice to the world's governments, spurred interdisciplinary research.[440] As part of the IPCC reports, scientists assess the scientific discussion that takes place in peer-reviewed journal articles.[441]

There is a near-complete scientific consensus that the climate is warming and that this is caused by human activities. As of 2019, agreement in recent literature reached over 99%.[436][437] No scientific body of national or international standing disagrees with this view.[442] Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change. National science academies have called on world leaders to cut global emissions.[443] The 2021 IPCC Assessment Report stated that it is "unequivocal" that climate change is caused by humans.[437]

See also

References

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  2. ^ IPCC AR6 WG1 Summary for Policymakers 2021, SPM-7
  3. ^ Forster et al. 2024, p. 2626: "The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced."
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  7. ^
    • IPCC SRCCL 2019, p. 7: "Since the pre-industrial period, the land surface air temperature has risen nearly twice as much as the global average temperature (high confidence). Climate change... contributed to desertification and land degradation in many regions (high confidence)."
    • IPCC AR6 WG2 SPM 2022, p. 9: "Observed increases in areas burned by wildfires have been attributed to human-induced climate change in some regions (medium to high confidence)"
  8. ^ IPCC SROCC 2019, p. 16: "Over the last decades, global warming has led to widespread shrinking of the cryosphere, with mass loss from ice sheets and glaciers (very high confidence), reductions in snow cover (high confidence) and Arctic sea ice extent and thickness (very high confidence), and increased permafrost temperature (very high confidence)."
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Sources

 This article incorporates text from a free content work. Licensed under CC BY-SA 3.0. Text taken from The status of women in agrifood systems – Overview​, FAO, FAO.

IPCC reports

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Fifth Assessment report

Special Report: Global Warming of 1.5 °C

Special Report: Climate change and Land

Special Report: The Ocean and Cryosphere in a Changing Climate

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