Editing Causes of climate change (section)

===Carbon sinks ===
[[File:Carbon Sources and Sinks.svg|thumb|right|{{CO2}} sources and sinks since 1880. While there is little debate that excess carbon dioxide in the industrial era has mostly come from burning fossil fuels, the future strength of land and ocean carbon sinks is an area of study.<ref>{{cite web |title=CO2 is making Earth greener—for now |url=https://climate.nasa.gov/news/2436/co2-is-making-earth-greenerfor-now/ |url-status=live |archive-url=https://web.archive.org/web/20200227173022/https://climate.nasa.gov/news/2436/co2-is-making-earth-greenerfor-now/ |archive-date=27 February 2020 |access-date=28 February 2020 |publisher=NASA}}</ref>]]
The Earth's surface absorbs {{CO2}} as part of the [[carbon cycle]]. Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant [[carbon sink]] for {{CO2}}. Land-surface 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 also serves as a significant carbon sink via a two-step process. First, {{CO2}} dissolves in the surface water. Afterwards, the ocean's [[Thermohaline circulation|overturning circulation]] distributes it deep into the ocean's interior, where it accumulates over time as part of the [[carbon cycle]]. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted {{CO2}}.<ref name=":0" />{{Rp|450|date=November 2012}} Thus, around half of human-caused {{CO2}} emissions have been absorbed by land plants and by the oceans.<ref>{{harvnb|Climate.gov, 23 June|2022|ps=:"Carbon cycle experts estimate that natural "sinks"—processes that remove carbon from the atmosphere—on land and in the ocean absorbed the equivalent of about half of the carbon dioxide we emitted each year in the 2011–2020 decade."}}</ref>

This fraction of absorbed emissions is not static. 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%.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=TS-122|loc=Box TS.5, Figure 1}}</ref> 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 [[Soil carbon feedback|when they are warmer]].<ref>{{harvnb|Melillo|Frey|DeAngelis|Werner|2017}}: Our first-order estimate of a warming-induced loss of 190 Pg of soil carbon over the 21st century is equivalent to the past two decades of carbon emissions from fossil fuel burning.</ref><ref>{{harvnb|IPCC SRCCL Ch2|2019|pp=133, 144}}.</ref> 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.{{sfn|USGCRP Chapter 2|2017|pp=93–95}}<ref name="Liu2022">{{cite journal |last1=Liu |first1=Y. |last2=Moore |first2=J. K. |last3=Primeau |first3=F. |last4=Wang |first4=W. L. |date=22 December 2022 |title=Reduced CO2 uptake and growing nutrient sequestration from slowing overturning circulation |journal=Nature Climate Change |volume=13 |pages=83–90 |doi=10.1038/s41558-022-01555-7 |osti=2242376 |s2cid=255028552 }}</ref><ref name="PearceYale3602023">{{cite web |last=Pearce |first=Fred |date=18 April 2023 |title=New Research Sparks Concerns That Ocean Circulation Will Collapse |url=https://e360.yale.edu/features/climate-change-ocean-circulation-collapse-antarctica |language=en |access-date=3 February 2024 }}</ref>