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'{{Short description|Sub-cycle of the larger global carbon cycle}} {{Use dmy dates|date=September 2019}} {{About|movement of carbon in and around permafrost|other aspects of permafrost|permafrost}} [[File:Schuur_2022_permafrost_carbon_literature.jpeg|thumb|The annual number of scientific research papers published on the subject of permafrost carbon has grown from next to nothing around 1990 to around 400 by 2020.<ref name="Schuur2022" /> ]] {{Carbon cycle|By regions}} The '''permafrost carbon cycle''' or '''Arctic carbon cycle''' is a sub-cycle of the larger global [[carbon cycle]]. [[Permafrost]] is defined as subsurface material that remains below 0^o C (32^o F) for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir, one which was often neglected in the initial research determining global terrestrial carbon reservoirs. Since the start of the 2000s, however, far more attention has been paid to the subject,<ref name=zimov>{{Cite journal|vauthors=Zimov SA, Schuur EA, Chapin FS |title=Climate change. Permafrost and the global carbon budget |journal=Science |volume=312 |issue=5780 |pages=1612–3 |date=June 2006 |pmid=16778046 |doi=10.1126/science.1128908 |s2cid=129667039 }}</ref> with an enormous growth both in general attention and in the scientific research output.<ref name="Schuur2022" /> The permafrost carbon cycle deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to [[Atmosphere of Earth|the atmosphere]], back to vegetation, and, finally, back to permafrost soils through burial and sedimentation due to cryogenic processes. Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle. The cycle includes the exchange of [[carbon dioxide]] and [[methane]] between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water as methane, [[dissolved organic carbon]], [[dissolved inorganic carbon]], [[particulate inorganic carbon]], and [[particulate organic carbon]].<ref>{{Cite journal|doi=10.1890/08-2025.1 |author=McGuire, A.D., Anderson, L.G., Christensen, T.R., Dallimore, S., Guo, L., Hayes, D.J., Heimann, M., Lorenson, T.D., Macdonald, R.W., and Roulet, N. |title=Sensitivity of the carbon cycle in the Arctic to climate change |journal=Ecological Monographs |volume=79 |issue=4 |pages=523–555 |year=2009 |bibcode=2009EcoM...79..523M |hdl=11858/00-001M-0000-000E-D87B-C |s2cid=1779296 |hdl-access=free }}</ref> ==Storage== Soils, in general, are the largest reservoirs of carbon in [[Ecosystem|terrestrial ecosystem]]s. This is also true for soils in the Arctic that are underlain by permafrost. In 2003, Tarnocai, et al. used the Northern and Mid Latitudes Soil Database to make a determination of carbon stocks in [[Gelisols|cryosols]]—soils containing permafrost within two meters of the soil surface.<ref name=kimble>{{Cite book|author=Tarnocai, C., Kimble, J., Broll, G. |chapter=Determining carbon stocks in Cryosols using the Northern and Mid Latitudes Soil Database |chapter-url=http://www.arlis.org/docs/vol1/ICOP/55700698/Pdf/Chapter_198.pdf |editor1=Phillips, Marcia |editor2=Springman, Sarah M |editor3=Arenson, Lukas U |title=Permafrost: Proceedings of the 8th International Conference on Permafrost, Zurich, Switzerland, 21–25 July 2003 |pages=1129–34 |publisher=Momenta |year=2003 |location=London |isbn=978-90-5809-584-8}}</ref> Permafrost affected soils cover nearly 9% of the Earth's land area, yet store between 25 and 50% of the soil organic carbon. These estimates show that permafrost soils are an important carbon pool.<ref name=bockheim>{{Cite journal |doi=10.2136/sssaj2007.0070N |author1=Bockheim, J.G. |author2=Hinkel, K.M. |name-list-style=amp |title=The importance of "Deep" organic carbon in permafrost-affected soils of Arctic Alaska |journal=Soil Science Society of America Journal |volume=71 |issue=6 |pages=1889–92 |year=2007 |url=http://soil.scijournals.org/cgi/content/abstract/71/6/1889 |bibcode=2007SSASJ..71.1889B |access-date=5 June 2010 |archive-url=https://web.archive.org/web/20090717063627/http://soil.scijournals.org/cgi/content/abstract/71/6/1889 |archive-date=17 July 2009 }}</ref> These soils not only contain large amounts of carbon, but also sequester carbon through [[cryoturbation]] and cryogenic processes.<ref name=kimble/><ref name=tarnocai/> ===Processes=== Carbon is not produced by permafrost. Organic carbon derived from terrestrial vegetation must be incorporated into the soil column and subsequently be incorporated into permafrost to be effectively stored. Because permafrost responds to climate changes slowly, carbon storage removes carbon from the atmosphere for long periods of time. [[Radiocarbon]] dating techniques reveal that carbon within permafrost is often thousands of years old.<ref name=guo/><ref name=nowinski/> Carbon storage in permafrost is the result of two primary processes. *The first process that captures carbon and stores it is [[syngenetic permafrost growth]].<ref>{{Cite journal|last1=Anderson|first1=D. A.|last2=Bray|first2=M. T.|last3=French|first3=H. M.|last4=Shur|first4=Y.|date=1 October 2004|title=Syngenetic permafrost growth: cryostratigraphic observations from the CRREL tunnel near Fairbanks, Alaska|journal=Permafrost and Periglacial Processes|language=en|volume=15|issue=4|pages=339–347|doi=10.1002/ppp.486|bibcode=2004PPPr...15..339S |s2cid=128478370 |issn=1099-1530}}</ref> This process is the result of a constant active layer where thickness and energy exchange between permafrost, active layer, biosphere, and atmosphere, resulting in the vertical increase of the soil surface elevation. This aggradation of soil is the result of [[Aeolian processes|aeolian]] or [[fluvial]] sedimentation and/or [[peat]] formation. Peat accumulation rates are as high as 0.5mm/yr while sedimentation may cause a rise of 0.7mm/yr. Thick silt deposits resulting from abundant loess deposition during the [[last glacial maximum]] form thick carbon-rich soils known as [[yedoma]].<ref name=schuur/> As this process occurs, the organic and mineral soil that is deposited is incorporated into the permafrost as the permafrost surface rises. *The second process responsible for storing carbon is [[cryoturbation]], the mixing of soil due to freeze-thaw cycles. Cryoturbation moves carbon from the surface to depths within the soil profile. [[Frost heaving]] is the most common form of cryoturbation. Eventually, carbon that originates at the surface moves deep enough into the active layer to be incorporated into permafrost. When cryoturbation and the deposition of sediments act together carbon storage rates increase.<ref name=schuur/> ===Current estimates=== [[File:Hugelius_2020_peatland_projections.jpg|thumb|Permafrost peatlands under varying extent of global warming, and the resultant emissions as a fraction of anthropogenic emissions needed to cause that extent of warming.<ref name="Hugelius2020" />]] It is estimated that the total soil organic carbon (SOC) stock in northern circumpolar permafrost region equals around 1,460–1,600 [[Kilogram#SI multiples|Pg]].<ref name=tarnocai>{{Cite journal |author=Tarnocai, C., Canadell, J.G., Schuur, E.A.G., Kuhry, P., Mazhitova, G., and Zimov, S. |title=Soil organic carbon pools in the northern circumpolar permafrost region |journal=Global Biogeochemical Cycles |volume=23 |issue=2 |year=2009 |pages=GB2023 |doi=10.1029/2008GB003327 |bibcode=2009GBioC..23.2023T |doi-access=free }}</ref> (1 Pg = 1 Gt = 10¹⁵g)<ref>{{Cite journal|last1=Hugelius|first1=G.|last2=Strauss|first2=J.|last3=Zubrzycki|first3=S.|last4=Harden|first4=J. W.|author-link4=Jennifer Harden|last5=Schuur|first5=E. A. G.|last6=Ping|first6=C.-L.|last7=Schirrmeister|first7=L.|last8=Grosse|first8=G.|last9=Michaelson|first9=G. J.|last10=Koven|first10=C. D.|last11=O'Donnell|first11=J. A.|date=2014-12-01|title=Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps|journal=Biogeosciences|volume=11|issue=23|pages=6573–6593|doi=10.5194/bg-11-6573-2014|bibcode=2014BGeo...11.6573H|s2cid=14158339 |issn=1726-4189|doi-access=free}}</ref><ref name="ARC2019">{{Cite web|title=Permafrost and the Global Carbon Cycle|url=https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/844/Permafrost-and-the-Global-Carbon-Cycle|access-date=2021-05-18|website=Arctic Program|date=31 October 2019 |language=en-US}}</ref> With the [[Tibetan Plateau]] carbon content included, the total carbon pools in the permafrost of the Northern Hemisphere is likely to be around 1832 Gt.<ref>{{cite journal |last1=Mu |first1=C. |last2=Zhang |first2=T. |last3=Wu |first3=Q. |last4=Peng |first4=X. |last5=Cao |first5=B. |last6=Zhang |first6=X. |last7=Cao |first7=B. |last8=Cheng |first8=G. |title=Editorial: Organic carbon pools in permafrost regions on the Qinghai–Xizang (Tibetan) Plateau |journal=The Cryosphere |date=6 March 2015 |volume=9 |issue=2 |pages=479–486 |doi=10.5194/tc-9-479-2015 |bibcode=2015TCry....9..479M |url=https://tc.copernicus.org/articles/9/479/2015/tc-9-479-2015.pdf |access-date=5 December 2022 |doi-access=free }}</ref> This estimation of the amount of carbon stored in permafrost soils is more than double the amount currently in the atmosphere.<ref name=zimov/> Soil column in the permafrost soils is generally broken into three horizons, 0–30&nbsp;cm, 0–100&nbsp;cm, and 1–300&nbsp;cm. The uppermost horizon (0–30&nbsp;cm) contains approximately 200 Pg of organic carbon. The 0–100&nbsp;cm horizon contains an estimated 500 Pg of organic carbon, and the 0–300&nbsp;cm horizon contains an estimated 1024 Pg of organic carbon. These estimates more than doubled the previously known carbon pools in permafrost soils.<ref name=kimble/><ref name=bockheim/><ref name=tarnocai/> Additional carbon stocks exist in [[yedoma]] (400 Pg), carbon rich [[loess]] deposits found throughout Siberia and isolated regions of North America, and deltaic deposits (240 Pg) throughout the Arctic. These deposits are generally deeper than the 3 m investigated in traditional studies.<ref name=tarnocai/> Many concerns arise because of the large amount of carbon stored in permafrost soils. Until recently, the amount of carbon present in permafrost was not taken into account in climate models and global carbon budgets.<ref name=zimov/><ref name=schuur/> ==Carbon release from the permafrost== Carbon is continually cycling between soils, vegetation, and the atmosphere. As climate change increases mean annual air temperatures throughout the Arctic, it extends permafrost thaw and deepens the active layer, exposing old carbon that has been in storage for decades to millennia to biogenic processes which facilitate its entrance into the atmosphere. In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per {{convert|1|C-change|F-change}}of global warming.<ref name="AR6_WG1_Chapter922">Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G.  Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf Chapter 9: Ocean, Cryosphere and Sea Level Change]. 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, NY, USA, pp. 1211–1362, doi:10.1017/9781009157896.011.</ref>{{rp|1283}} According to the [[IPCC Sixth Assessment Report]], there is high confidence that global warming over the last few decades has led to widespread increases in permafrost temperature.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} Observed warming was up to {{convert|3|C-change|F-change}} in parts of Northern Alaska (early 1980s to mid-2000s) and up to {{convert|2|C-change|F-change}} in parts of the Russian European North (1970–2020), and active layer thickness has increased in the European and Russian Arctic across the 21st century and at high elevation areas in Europe and Asia since the 1990s.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} In [[Yukon]], the zone of continuous permafrost might have moved {{convert|100|km}} poleward since 1899, but accurate records only go back 30 years. Based on high agreement across model projections, fundamental process understanding, and paleoclimate evidence, it is virtually certain that permafrost extent and volume will continue to shrink as global climate warms.<ref name="AR6_WG1_Chapter922" />{{rp|1283}} [[File:Douglas_2020_precipitation_layers.png|thumb|left|Greater summer precipitation increases the depth of permafrost layer subject to thaw, in different Arctic permafrost environments.<ref name="Douglas2020" />]] Carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it a [[Climate change feedback#Positive feedbacks|positive climate change feedback]]. The warming also intensifies Arctic [[water cycle]], and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.<ref name="Douglas2020">{{Cite journal |last1=Douglas |first1=Thomas A. |last2=Turetsky |first2=Merritt R. |last3=Koven |first3=Charles D. |date=24 July 2020 |title=Increased rainfall stimulates permafrost thaw across a variety of Interior Alaskan boreal ecosystems |journal=npj Climate and Atmospheric Science |volume=3 |issue=1 |page=5626 |doi=10.1038/s41612-020-0130-4 |doi-access=free |bibcode=2020npCAS...3...28D }}</ref> The amount of carbon that will be released from warming conditions depends on depth of thaw, carbon content within the thawed soil, physical changes to the environment<ref name=nowinski>{{Cite journal|vauthors=Nowinski NS, Taneva L, [[Susan Trumbore|Trumbore SE]], Welker JM |title=Decomposition of old organic matter as a result of deeper active layers in a snow depth manipulation experiment |journal=Oecologia |volume=163 |issue=3 |pages=785–92 |date=January 2010 |pmid=20084398 |pmc=2886135 |doi=10.1007/s00442-009-1556-x |bibcode=2010Oecol.163..785N }}</ref> and microbial and vegetation activity in the soil. Microbial respiration is the primary process through which old permafrost carbon is re-activated and enters the atmosphere. The rate of microbial decomposition within organic soils, including thawed permafrost, depends on environmental controls, such as soil temperature, moisture availability, nutrient availability, and oxygen availability.<ref name=schuur>{{Cite journal|author=Schuur, E.A.G., Bockheim, J., Canadell, J.G., Euskirchen, E., Field, C.B., Goryachkin, S.V., Hagemann, S., Kuhry, P., Lafleur, P.M., Lee, H., Mazhitova, G., Nelson, F.E., Rinke, A., Romanovsky, V.E., Skiklomanov, N., Tarnocai, C., Venevsky, S., Vogel, J.G., and Zimov, S.A. |title=Vulnerability of Permafrost Carbon to Climate Change: Implications for the Global Carbon Cycle |journal=BioScience |volume=58 |issue=8 |pages=701–714 |year=2008 |doi=10.1641/B580807 |doi-access=free }}</ref> In particular, sufficient concentrations of iron oxides in some permafrost soils can inhibit microbial respiration and prevent carbon mobilization: however, this protection only lasts until carbon is separated from the iron oxides by Fe-reducing bacteria, which is only a matter of time under the typical conditions.<ref>{{Cite journal |last1=Lim |first1=Artem G. |last2=Loiko |first2=Sergey V. |last3=Pokrovsky |first3=Oleg S. |date=10 January 2023 |title=Interactions between organic matter and Fe oxides at soil micro-interfaces: Quantification, associations, and influencing factors |journal=Science of the Total Environment |volume=3 |page=158710 |doi=10.1016/j.scitotenv.2022.158710|pmid=36099954 |s2cid=252221350 |doi-access=free }}</ref> Depending on the soil type, [[Iron(III) oxide]] can boost oxidation of methane to carbon dioxide in the soil, but it can also amplify methane production by acetotrophs: these soil processes are not yet fully understood.<ref>{{Cite journal |last1=Patzner |first1=Monique S. |last2=Mueller |first2=Carsten W. |last3=Malusova |first3=Miroslava |last4=Baur |first4=Moritz |last5=Nikeleit |first5=Verena |last6=Scholten |first6=Thomas |last7=Hoeschen |first7=Carmen |last8=Byrne |first8=James M. |last9=Borch |first9=Thomas |last10=Kappler |first10=Andreas |last11=Bryce |first11=Casey |date=10 December 2020 |title=Iron mineral dissolution releases iron and associated organic carbon during permafrost thaw |journal=Nature Communications |volume=11 |issue=1 |page=6329 |doi=10.1038/s41467-020-20102-6|pmid=33303752 |pmc=7729879 |bibcode=2020NatCo..11.6329P }}</ref> Altogether, the likelihood of the entire carbon pool mobilizing and entering the atmosphere is low despite the large volumes stored in the soil. Although temperatures will increase, this does not imply complete loss of permafrost and mobilization of the entire carbon pool. Much of the ground underlain by permafrost will remain frozen even if warming temperatures increase the thaw depth or increase thermokarsting and permafrost degradation.<ref name=bockheim/> Moreover, other elements such as [[iron]] and [[aluminum]] can [[adsorbtion|adsorb]] some of the mobilized [[soil carbon]] before it reaches the atmosphere, and they are particularly prominent in the mineral sand layers which often overlay permafrost.<ref>{{cite journal | doi=10.1016/j.geoderma.2021.115601 | title=Sizable pool of labile organic carbon in peat and mineral soils of permafrost peatlands, western Siberia | date=2022 | last1=Lim | first1=Artem G. | last2=Loiko | first2=Sergey V. | last3=Pokrovsky | first3=Oleg S. | journal=Geoderma | volume=409 | bibcode=2022Geode.409k5601L }}</ref> On the other hand, once the permafrost area thaws, it will not go back to being permafrost for centuries even if the temperature increase reversed, making it one of the best-known examples of [[tipping points in the climate system]]. A 1993 study suggested that while the tundra was a [[carbon sink]] until the end of the 1970s, it had already transitioned to a net carbon source by the time the study concluded.<ref name="Oechel1993">{{cite journal | first1=Walter C.|last1=Oechel|first2=Steven J. |last2=Hastings |first3=George |last3=Vourlrtis |first4=Mitchell |last4=Jenkins |first5=George |last5=Riechers |first6=Nancy|last6=Grulkelast|display-authors=4 | date = 1993 | title = Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source | journal = [[Nature (journal)|Nature]] | volume = 361 | issue = 6412 | pages = 520–523 | doi = 10.1038/361520a0 |bibcode=1993Natur.361..520O |s2cid=4339256}}</ref> The 2019 Arctic Report Card estimated that Arctic permafrost releases between 0.3 and 0.6 Pg C per year.<ref name="ARC2019" /> That same year, a study settled on the 0.6 Pg C figure, as the net difference between the annual emissions of 1,66 Pg C during the winter season (October–April), and the model-estimated vegetation carbon uptake of 1 Pg C during the growing season. It estimated that under [[Representative Concentration Pathway|RCP]] 8.5, a scenario of continually accelerating greenhouse gas emissions, winter {{CO2}} emissions from the northern permafrost domain would increase 41% by 2100. Under the "intermediate" scenario RCP 4.5, where greenhouse gas emissions peak and plateau within the next two decades, before gradually declining for the rest of the century (a rate of mitigation deeply insufficient to meet the [[Paris Agreement]] goals) permafrost carbon emissions would increase by 17%.<ref>{{Cite journal|last1=Natali|first1=Susan M.|last2=Watts|first2=Jennifer D.|last3=Rogers|first3=Brendan M.|last4=Potter|first4=Stefano|last5=Ludwig|first5=Sarah M.|last6=Selbmann|first6=Anne-Katrin|last7=Sullivan|first7=Patrick F.|last8=Abbott|first8=Benjamin W.|last9=Arndt|first9=Kyle A.|last10=Birch|first10=Leah|last11=Björkman|first11=Mats P.|date=2019-10-21|title=Large loss of CO2 in winter observed across the northern permafrost region|journal=Nature Climate Change|volume=9|issue=11|pages=852–857|doi=10.1038/s41558-019-0592-8|pmid=35069807|pmc=8781060|bibcode=2019NatCC...9..852N|hdl=10037/17795|s2cid=204812327|issn=1758-678X}}</ref> In 2022, this was challenged by a study which used a record of atmospheric observations between 1980 and 2017, and found that permafrost regions have been gaining carbon on net, as process-based models underestimated net CO₂ uptake in the permafrost regions and overestimated it in the forested regions, where increased respiration in response to warming offsets more of the gains than was previously understood.<ref name="Liu2022">{{Cite journal |last1=Liu |first1=Zhihua |last2=Kimball |first2=John S. |last3=Ballantyne |first3=Ashley P. |last4=Parazoo |first4=Nicholas C. |last5=Wang |first5=Wen J. |last6=Bastos |first6=Ana |last7=Madani |first7=Nima |last8=Natali |first8=Susan M. |last9=Watts |first9=Jennifer D. |last10=Rogers |first10=Brendan M. |last11=Ciais |first11=Philippe |last12=Yu |first12=Kailiang |last13=Virkkala |first13=Anna-Maria |last14=Chevallier |first14=Frederic |last15=Peters |first15=Wouter |last16=Patra |first16=Prabir K. |last17=Chandra |first17=Naveen |date=2019-10-21|title=Respiratory loss during late-growing season determines the net carbon dioxide sink in northern permafrost regions |journal=Nature Communications |volume=13 |issue=1 |page=5626 |doi=10.1038/s41467-022-33293-x|pmid=36163194 |pmc=9512808 }}</ref> Notably, estimates of carbon release alone do not fully represent the impact of permafrost thaw on climate change. This is because carbon can either be released as carbon dioxide (CO₂) or methane (CH₄). [[Aerobic respiration]] releases carbon dioxide, while [[anaerobic respiration]] releases methane. This is a substantial difference, as while biogenic methane lasts less than 12 years in the atmosphere, its [[global warming potential]] is around 80 times larger than that of CO₂ over a 20-year period and between 28 and 40 times larger over a 100-year period. ===Carbon dioxide emissions=== [[File:Liu_2022_permafrost_tree_cover.png|thumb|Recent observations suggest that {{CO2}} absorption had been increasing at a faster rate over the areas with a lot of permafrost and limited tree cover than over the areas with extensive tree cover.<ref name="Liu2022" />]] Most of the permafrost soil are oxic and provide a suitable environment for aerobic microbial respiration. As such, carbon dioxide emissions account for the overwhelming majority of permafrost emissions and of the Arctic emissions in general.<ref>{{Cite journal |last1=Miner |first1=Kimberley R. |last2=Turetsky |first2=Merritt R. |last3=Malina |first3=Edward |last4=Bartsch |first4=Annett |last5=Tamminen |first5=Johanna |last6=McGuire |first6=A. David |last7=Fix |first7=Andreas |last8=Sweeney |first8=Colm |last9=Elder |first9=Clayton D. |last10=Miller |first10=Charles E. |date=11 January 2022|title=Permafrost carbon emissions in a changing Arctic |url=https://www.nature.com/articles/s43017-021-00230-3 |journal=Nature Reviews Earth & Environment |volume=13 |issue=1 |pages=55–67 |doi=10.1038/s43017-021-00230-3|bibcode=2022NRvEE...3...55M |s2cid=245917526 }}</ref> There's some debate over whether the observed emissions from permafrost soils primarily constitute microbial respiration of ancient carbon, or simply greater respiration of modern-day carbon (i.e. leaf litter), due to warmer soils intensifying microbial metabolism. Studies published in the early 2020s indicate that while soil microbiota still primarily consumes and respires modern carbon when plants grow during the spring and summer, these microorganisms then sustain themselves on ancient carbon during the winter, releasing it into the atmosphere.<ref>{{Cite journal |last1=Estop-Aragonés |first1= Cristian |last2=Olefeldt |first2=David |display-authors=etal |date=2 September 2020 |title=Assessing the Potential for Mobilization of Old Soil Carbon After Permafrost Thaw: A Synthesis of 14C Measurements From the Northern Permafrost Region |journal=Global Biogeochemical Cycles |volume=34 |issue=9 |doi=10.1029/2020GB006672|bibcode= 2020GBioC..3406672E |s2cid= 225258236 |doi-access=free }}</ref><ref>{{Cite journal |last1=Pedron |first1=Shawn A. |last2=Welker |first2=J. M. |last3=Euskirchen |first3=E. S. |last4=Klein |first4=E. S. |last5=Walker |first5=J. C. |last6=Xu |first6=X. |last7=Czimczik |first7=C. I. |date=14 March 2022 |title=Closing the Winter Gap—Year-Round Measurements of Soil CO2 Emission Sources in Arctic Tundra |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL097347 |journal=Geophysical Research Letters |volume=49 |issue=6 |doi=10.1029/2021GL097347|bibcode=2022GeoRL..4997347P |s2cid=247491567 }}</ref> On the other hand, former permafrost areas consistently see increased vegetation growth, or primary production, as plants can set down deeper roots in the thawed soil and grow larger and uptake more carbon. This is generally the main counteracting feedback on permafrost carbon emissions. However, in areas with streams and other waterways, more of their leaf litter enters those waterways, increasing their dissolved organic carbon content. Leaching of soil organic carbon from permafrost soils is also accelerated by warming climate and by erosion along river and stream banks freeing the carbon from the previously frozen soil.<ref name=guo>{{Cite journal|author=Guo, L., Chien-Lu Ping, and Macdonald, R.W. |title=Mobilization pathways of organic carbon from permafrost to arctic rivers in a changing climate |journal=Geophysical Research Letters |volume=34 |issue=13 |pages=L13603 |date=July 2007 |doi=10.1029/2007GL030689 |bibcode=2007GeoRL..3413603G|s2cid=129757480 }}</ref> Moreover, thawed areas become more vulnerable to wildfires, which alter landscape and release large quantities of stored organic carbon through combustion. As these fires burn, they remove organic matter from the surface. Removal of the protective organic mat that insulates the soil exposes the underlying soil and permafrost to increased [[solar radiation]], which in turn increases the soil temperature, active layer thickness, and changes soil moisture. Changes in the soil moisture and saturation alter the ratio of [[oxic]] to anoxic decomposition within the soil.<ref name=meyers>{{Cite journal|doi=10.1029/2007JG000423 |author=Meyers-Smith, I.H., McGuire, A.D., Harden, J.W., Chapin, F.S. |title=Influence of disturbance on carbon exchange in a permafrost collapse and adjacent burned forest |journal=Journal of Geophysical Research |volume=112 |issue=G4 |pages=G04017 |year=2007 |bibcode=2007JGRG..112.4017M|url=https://www.pure.ed.ac.uk/ws/files/8365805/PDF_Myers_Smith.et.al2007.pdf |doi-access=free }}</ref> A hypothesis promoted by [[Sergey Zimov]] is that the reduction of herds of large herbivores has increased the ratio of energy emission and energy absorption tundra (energy balance) in a manner that increases the tendency for net thawing of permafrost.<ref>{{cite web|title=Mammoth steppe: a high-productivity phenomenon|author=S.A. Zimov, N.S. Zimov, A.N. Tikhonov, [[F. Stuart Chapin III|F.S. Chapin III]]|url=http://www.lter.uaf.edu/pdf/1754_Zimov_Zimov_2012.pdf|year=2012|publisher=In: [[Quaternary Science Reviews]], vol.&nbsp;57, 4&nbsp;December&nbsp;2012, p.&nbsp;42&nbsp;fig.17|access-date=17 October 2014|archive-url=https://web.archive.org/web/20160304103247/http://www.lter.uaf.edu/pdf/1754_Zimov_Zimov_2012.pdf|archive-date=4 March 2016}}</ref> He is testing this hypothesis in an experiment at [[Pleistocene Park]], a nature reserve in northeastern Siberia.<ref>Sergey A. Zimov (6 May 2005): [https://www.science.org/doi/full/10.1126/science.1113442 "Pleistocene Park: Return of the Mammoth's Ecosystem."] {{Webarchive|url=https://web.archive.org/web/20170220222928/http://science.sciencemag.org/content/308/5723/796.1.full |date=2017-02-20 }} In: ''[[Science (journal)|Science]]'', pages 796–798. Article also to be found in [http://www.pleistocenepark.ru/en/materials/ www.pleistocenepark.ru/en/ – Materials.] {{Webarchive|url=https://web.archive.org/web/20161103172534/http://www.pleistocenepark.ru/en/materials/ |date=2016-11-03 }} Retrieved 5 May 2013.</ref> On the other hand, warming allows the [[beaver]]s to extend their habitat further north, where their [[Beaver dam#Effects|dams impair]] boat travel, impact access to food, affect water quality, and endanger downstream fish populations.<ref name=Guardian_20220104/> Pools formed by the dams store heat, thus changing local [[hydrology]] and causing localized permafrost thaw.<ref name=Guardian_20220104>{{cite news |last1=Milman |first1=Oliver |title=Dam it: beavers head north to the Arctic as tundra continues to heat up |url=https://www.theguardian.com/world/2022/jan/04/beavers-arctic-north-climate-crisis |newspaper=The Guardian |date=January 4, 2022 |archive-url=https://web.archive.org/web/20220104220623/https://www.theguardian.com/world/2022/jan/04/beavers-arctic-north-climate-crisis |archive-date=January 4, 2022 |url-status=live }}</ref> ===Methane emissions=== {{See also|Arctic methane emissions}} [[File:Bernhard_2022_RTS_activity.png|thumb|Carbon cycle accelerates in the wake of abrupt thaw (orange) relative to the previous state of the area (blue, black).<ref name="Bernhard2022" />]] Global warming in the Arctic accelerates methane release from both existing stores and [[methanogenesis]] in rotting [[Biomass (ecology)|biomass]].<ref>{{Cite journal| doi = 10.1029/2007JG000569| title = Methane production and bubble emissions from arctic lakes: Isotopic implications for source pathways and ages |year = 2008| last1 = Walter | first1 = K. M.| last2 = Chanton | first2 = J. P. |author-link2=Jeff Chanton| last3 = Chapin | first3 = F. S.| last4 = Schuur | first4 = E. A. G.| last5 = Zimov | first5 = S. A.| journal = Journal of Geophysical Research| volume = 113| issue = G3 | pages = G00A08 | bibcode=2008JGRG..113.0A08W| doi-access = free}}</ref> Methanogenesis requires thoroughly anaerobic environments, which slows down the mobilization of old carbon. A 2015 ''[[Nature (magazine)|Nature]]'' review estimated that the cumulative emissions from thawed anaerobic permafrost sites were 75–85% lower than the cumulative emissions from aerobic sites, and that even there, methane emissions amounted to only 3% to 7% of CO₂ emitted in situ. While they represented between 25% and 45% of the CO₂'s potential impact on climate over a 100-year timescale, the review concluded that aerobic permafrost thaw still had a greater warming impact overall.<ref>{{Cite journal|last1=Schuur |first1=E. A. G. |last2=McGuire |first2=A. D. |last3=Schädel |first3=C. |last4=Grosse |first4=G. |last5=Harden |first5=J. W. |display-authors=etal |date=9 April 2015|title=Climate change and the permafrost carbon feedback|url=https://www.nature.com/articles/nature14338 |journal=Nature |volume=520 |issue=7546 |pages=171–179 |doi=10.1038/nature14338|pmid=25855454 |bibcode=2015Natur.520..171S |hdl=1874/330256 |s2cid=4460926 }}</ref> In 2018, however, another study in ''[[Nature Climate Change]]'' performed seven-year incubation experiments and found that methane production became equivalent to CO₂ production once a methanogenic microbial community became established at the anaerobic site. This finding had substantially raised the overall warming impact represented by anaerobic thaw sites.<ref>{{Cite journal|last1=Pfeiffer|first1=Eva-Maria|last2=Grigoriev|first2=Mikhail N. |last3=Liebner |first3=Susanne |last4=Beer |first4=Christian |last5=Knoblauch|first5=Christian|date=April 2018|title=Methane production as key to the greenhouse gas budget of thawing permafrost|journal=Nature Climate Change|volume=8|issue=4|pages=309–312|doi=10.1038/s41558-018-0095-z|issn=1758-6798|bibcode=2018NatCC...8..309K|s2cid=90764924|url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:3094899}}</ref> Since methanogenesis requires anaerobic environments, it is frequently associated with Arctic lakes, where the emergence of bubbles of methane can be observed.<ref>{{cite journal|journal=Nature|volume=443|issue=7107|pages=71–75|date=7 September 2006| doi=10.1038/nature05040|pmid=16957728|title=Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming |first1=KM |last1=Walter |first2=SA |last2=Zimov |first3=JP |last3=Chanton |first4=D |last4=Verbyla |first5=FS III|last5=Chapin|display-authors=4|bibcode=2006Natur.443...71W|s2cid=4415304}}</ref><ref name="NYT Thaw">{{cite news|title=As Permafrost Thaws, Scientists Study the Risks|url=https://www.nytimes.com/2011/12/17/science/earth/warming-arctic-permafrost-fuels-climate-change-worries.html|access-date=December 17, 2011|newspaper=The New York Times|date=December 16, 2011|first=Justin|last=Gillis}}</ref> Lakes produced by the thaw of particularly ice-rich permafrost are known as [[thermokarst]] lakes. Not all of the methane produced in the sediment of a lake reaches the atmosphere, as it can get oxidized in the water column or even within the sediment itself:<ref>{{Cite journal |last1=Vigderovich |first1=Hanni |last2=Eckert |first2=Werner |last3=Elul |first3=Michal |last4=Rubin-Blum |first4=Maxim |last5=Elvert |first5=Marcus |last6=Sivan |first6=Orit |last7=Czimczik |first7=C. I. |date=2 May 2022 |title=Long-term incubations provide insight into the mechanisms of anaerobic oxidation of methane in methanogenic lake sediments |url=https://bg.copernicus.org/articles/19/2313/2022/ |journal=Biogeosciences |volume=19 |issue=8 |doi=10.1029/2021GL097347|bibcode=2022GeoRL..4997347P |s2cid=247491567 }}</ref> However, 2022 observations indicate that at least half of the methane produced within thermokarst lakes reaches the atmosphere.<ref>{{Cite journal |last1=Pellerin |first1=André |last2=Lotem |first2=Noam |last3=Anthony |first3=Katey Walter |last4=Russak |first4=Efrat Eliani |last5=Hasson |first5=Nicholas |last6=Røy |first6=Hans |last7=Chanton |first7=Jeffrey P. |last8=Sivan |first8=Orit |date=4 March 2022 |title=Methane production controls in a young thermokarst lake formed by abrupt permafrost thaw |journal=Global Change Biology |volume=28 |issue=10 |pages=3206–3221 |doi=10.1111/gcb.16151|pmid=35243729 |pmc=9310722 }}</ref> Another process which frequently results in substantial methane emissions is the [[erosion]] of permafrost-stabilized hillsides and their ultimate collapse.<ref>{{Cite journal|last=Turetsky|first=Merritt R.|date=2019-04-30|title=Permafrost collapse is accelerating carbon release|journal=Nature|volume=569|issue=7754|pages=32–34|bibcode=2019Natur.569...32T|doi=10.1038/d41586-019-01313-4|pmid=31040419|doi-access=free}}</ref> Altogether, these two processes - hillside collapse (also known as retrogressive thaw slump, or RTS) and thermokarst lake formation - are collectively described as abrupt thaw, as they can rapidly expose substantial volumes of soil to microbial respiration in a matter of days, as opposed to the gradual, cm by cm, thaw of formerly frozen soil which dominates across most permafrost environments. This rapidity was illustrated in 2019, when three permafrost sites which would have been safe from thawing under the "intermediate" [[Representative Concentration Pathway]] 4.5 for 70 more years had undergone abrupt thaw.<ref name="TGRomanovsky">{{Cite news|url=https://www.theguardian.com/environment/2019/jun/18/arctic-permafrost-canada-science-climate-crisis|title=Scientists shocked by Arctic permafrost thawing 70 years sooner than predicted|date=2019-06-18|work=The Guardian|access-date=2019-07-02|language=en-GB|issn=0261-3077}}</ref> Another example occurred in the wake of a 2020 Siberian heatwave, which was found to have increased RTS numbers 17-fold across the northern [[Taymyr Peninsula]] – from 82 to 1404, while the resultant soil carbon mobilization increased 28-fold, to an average of 11 grams of carbon per square meter per year across the peninsula (with a range between 5 and 38 grams).<ref name="Bernhard2022">{{Cite journal |last1=Bernhard |first1=Philipp |last2=Zwieback |first2=Simon |last3=Hajnsek |first3=Irena |date=2 May 2022 |title=Accelerated mobilization of organic carbon from retrogressive thaw slumps on the northern Taymyr Peninsula |url=https://tc.copernicus.org/articles/16/2819/2022/ |journal=The Cryosphere |volume= 16 |issue=7 |pages=2819–2835 |doi=10.5194/tc-16-2819-2022|bibcode=2022TCry...16.2819B |doi-access=free }}</ref> Until recently, Permafrost carbon feedback (PCF) modeling had mainly focused on gradual permafrost thaw, due to the difficulty of modelling abrupt thaw, and because of the flawed assumptions about the rates of methane production.<ref name=":5" /> Nevertheless, a study from 2018, by using field observations, radiocarbon dating, and remote sensing to account for [[thermokarst]] lakes, determined that abrupt thaw will more than double permafrost carbon emissions by 2100.<ref name=":6" /> And a second study from 2020, showed that under the scenario of continually accelerating emissions (RCP 8.5), abrupt thaw carbon emissions across 2.5 million km² are projected to provide the same feedback as gradual thaw of near-surface permafrost across the whole 18 million km² it occupies.<ref name=":5" /> Thus, abrupt thaw adds between 60 and 100 gigatonnes of carbon by 2300,<ref>{{Cite journal |vauthors=Turetsky MR, Abbott BW, Jones MC, Anthony KW, Olefeldt D, Schuur EA, Koven C, McGuire AD, Grosse G, Kuhry P, Hugelius G|date=May 2019 |title=Permafrost collapse is accelerating carbon release |journal=Nature |volume=569 |issue=7754 |pages=32–34 |doi=10.1038/d41586-019-01313-4|pmid=31040419 |bibcode=2019Natur.569...32T |doi-access=free }}</ref> increasing carbon emissions by ~125–190% when compared to gradual thaw alone.<ref name=":5">{{Cite journal|last1=Turetsky|first1=Merritt R.|last2=Abbott|first2=Benjamin W.|last3=Jones|first3=Miriam C.|last4=Anthony|first4=Katey Walter|last5=Olefeldt|first5=David|last6=Schuur|first6=Edward A. G.|last7=Grosse|first7=Guido|last8=Kuhry|first8=Peter|last9=Hugelius|first9=Gustaf|last10=Koven|first10=Charles|last11=Lawrence|first11=David M.|date=February 2020|title=Carbon release through abrupt permafrost thaw|journal=Nature Geoscience|volume=13|issue=2|pages=138–143|doi=10.1038/s41561-019-0526-0|bibcode=2020NatGe..13..138T|s2cid=213348269|issn=1752-0894}}</ref><ref name=":6">{{Cite journal|last1=Walter Anthony|first1=Katey|last2=Schneider von Deimling|first2=Thomas|last3=Nitze|first3=Ingmar|last4=Frolking|first4=Steve|last5=Emond|first5=Abraham|last6=Daanen|first6=Ronald|last7=Anthony|first7=Peter|last8=Lindgren|first8=Prajna|last9=Jones|first9=Benjamin|last10=Grosse|first10=Guido|date=2018-08-15|title=21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes|journal=Nature Communications|volume=9|issue=1|page=3262|doi=10.1038/s41467-018-05738-9|pmid=30111815|pmc=6093858|bibcode=2018NatCo...9.3262W|issn=2041-1723}}</ref> [[File:Hefferman_2022_bog_methane.png|thumb|left|Methane emissions from thawed permafrost appear to decrease as bog matures over time.<ref name="Heffernan2022" />]] However, there is still scientific debate about the rate and the trajectory of methane production in the thawed permafrost environments. For instance, a 2017 paper suggested that even in the thawing peatlands with frequent thermokarst lakes, less than 10% of methane emissions can be attributed to the old, thawed carbon, and the rest is anaerobic decomposition of modern carbon.<ref>{{Cite journal|last1=Cooper |first1=M. |last2=Estop-Aragonés |first2=C. |last3=Fisher |first3=J. |display-authors=etal|date=26 June 2017 |title=Limited contribution of permafrost carbon to methane release from thawing peatlands|url=https://www.nature.com/articles/nature14338 |journal=Nature Climate Change |volume=7 |issue=7 |pages=507–511 |doi=10.1038/nclimate3328|bibcode=2017NatCC...7..507C }}</ref> A follow-up study in 2018 had even suggested that increased uptake of carbon due to rapid peat formation in the thermokarst wetlands would compensate for the increased methane release.<ref>{{Cite journal |last1=Estop-Aragonés |first1=Cristian |last2=Cooper |first2=Mark D.A. |last3=Fisher |first3=James P. |display-authors=etal |date=March 2018 |title=Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands |journal=Soil Biology and Biochemistry |volume=118 |pages=115–129 |doi=10.1016/j.soilbio.2017.12.010|doi-access=free |bibcode=2018SBiBi.118..115E }}</ref> Another 2018 paper suggested that permafrost emissions are limited following thermokarst thaw, but are substantially greater in the aftermath of wildfires.<ref>{{Cite journal |last1=Estop-Aragonés |first1=Cristian |display-authors=etal|date=13 August 2018 |title=Respiration of aged soil carbon during fall in permafrost peatlands enhanced by active layer deepening following wildfire but limited following thermokarst |journal=Environmental Research Letters |volume=13 |issue=8 |page=085002 |doi=10.1088/1748-9326/aad5f0|bibcode=2018ERL....13h5002E |s2cid=158857491 |doi-access=free }}</ref> In 2022, a paper demonstrated that peatland methane emissions from permafrost thaw are initially quite high (82 milligrams of methane per square meter per day), but decline by nearly three times as the permafrost bog matures, suggesting a reduction in methane emissions in several decades to a century following abrupt thaw.<ref name="Heffernan2022">{{Cite journal|last1=Heffernan|first1=Liam |last2=Cavaco |first2= Maria A. |last3=Bhatia |first3=Maya P. |last4=Estop-Aragonés |first4= Cristian |last5=Knorr |first5=Klaus-Holger |last6=Olefeldt |first6=David |date=24 June 2022 |title=High peatland methane emissions following permafrost thaw: enhanced acetoclastic methanogenesis during early successional stages |url=https://bg.copernicus.org/articles/19/3051/2022/ |journal=Biogeosciences |volume=19 |issue=8 |pages=3051–3071 |doi=10.5194/bg-19-3051-2022|bibcode=2022BGeo...19.3051H |doi-access=free }}</ref> ===Subsea permafrost=== [[File:Sayedi_2020_subsea_projections.jpg|thumb|Carbon dioxide and methane (in {{CO2}} equivalent) emissions from subsea permafrost alone under the different [[Representative Concentration Pathway]] scenarios over time.<ref name=":4" />]] Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions.<ref>{{cite web|author=IPCC AR4|title=Climate Change 2007: Working Group I: The Physical Science Basis|date=2007|url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-7-2-4.html|access-date=12 April 2014|archive-url=https://web.archive.org/web/20140413125748/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-7-2-4.html|archive-date=13 April 2014}}</ref> Thus, it can be defined as "the unglaciated continental shelf areas exposed during the [[Last Glacial Maximum]] (LGM, ~26 500 BP) that are currently inundated". Large stocks of organic matter (OM) and methane ({{CH4}}) are accumulated below and within the subsea permafrost deposits.This source of methane is different from [[methane clathrate]]s, but contributes to the overall outcome and feedbacks in the Earth's climate system.<ref name=":4" /> The size of today's subsea permafrost has been estimated at 2 million km² (~1/5 of the terrestrial permafrost domain size), which constitutes a 30–50% reduction since the LGM. Containing around 560 GtC in OM and 45 GtC in CH₄, with a current release of 18 and 38 MtC per year respectively, which is due to the warming and thawing that the subsea permafrost domain has been experiencing since after the LGM (~14000 years ago). In fact, because the subsea permafrost systems responds at millennial timescales to climate warming, the current carbon fluxes it is emitting to the water are in response to climatic changes occurring after the LGM. Therefore, human-driven climate change effects on subsea permafrost will only be seen hundreds or thousands of years from today. According to predictions under a business-as-usual emissions scenario [[RCP8.5|RCP 8.5]], by 2100, 43 GtC could be released from the subsea permafrost domain, and 190 GtC by the year 2300. Whereas for the low emissions scenario RCP 2.6, 30% less emissions are estimated. This constitutes a significant anthropogenic-driven acceleration of carbon release in the upcoming centuries.<ref name=":4" /> ===Cumulative=== In 2011, preliminary computer analyses suggested that permafrost emissions could be equivalent to around 15% of anthropogenic emissions.<ref>{{cite news |title=As Permafrost Thaws, Scientists Study the Risks |first=Justin |last=Gillis |newspaper=The New York Times |date=December 16, 2011 |url=https://www.nytimes.com/2011/12/17/science/earth/warming-arctic-permafrost-fuels-climate-change-worries.html?pagewanted=all |access-date=2017-02-11 |archive-url=https://web.archive.org/web/20170519052405/http://www.nytimes.com/2011/12/17/science/earth/warming-arctic-permafrost-fuels-climate-change-worries.html?pagewanted=all |archive-date=2017-05-19 |url-status=live }}</ref> A 2018 perspectives article discussing [[tipping points in the climate system]] activated around {{convert|2|C-change|F-change}} of global warming suggested that at this threshold, permafrost thaw would add a further {{convert|0.09|C-change|F-change}} to global temperatures by 2100, with a range of {{convert|0.04-0.16|C-change|F-change}}<ref>{{Cite journal |last1=Schellnhuber |first1=Hans Joachim |last2=Winkelmann |first2=Ricarda |last3=Scheffer |first3=Marten |last4=Lade |first4=Steven J. |last5=Fetzer |first5=Ingo |last6=Donges |first6=Jonathan F. |last7=Crucifix |first7=Michel |last8=Cornell |first8=Sarah E. |last9=Barnosky |first9=Anthony D. |author-link9=Anthony David Barnosky |date=2018 |title=Trajectories of the Earth System in the Anthropocene |journal=[[Proceedings of the National Academy of Sciences]] |volume=115 |issue=33 |pages=8252–8259 |bibcode=2018PNAS..115.8252S |doi=10.1073/pnas.1810141115 |issn=0027-8424 |pmc=6099852 |pmid=30082409 |doi-access=free}}</ref> In 2021, another study estimated that in a future where [[net zero|zero emissions]] were reached following an emission of a further 1000 Pg C into the atmosphere (a scenario where temperatures ordinarily stay stable after the last emission, or start to decline slowly) permafrost carbon would add {{convert|0.06|C-change|F-change}} (with a range of {{convert|0.02-0.14|C-change|F-change}}) 50 years after the last anthropogenic emission, {{convert|0.09|C-change|F-change}} ({{convert|0.04-0.21|C-change|F-change}}) 100 years later and {{convert|0.27|C-change|F-change}} ({{convert|0.12-0.49|C-change|F-change}}) 500 years later.<ref>{{Cite journal |last1=MacDougall |first1=Andrew H. |date=10 September 2021 |title=Estimated effect of the permafrost carbon feedback on the zero emissions commitment to climate change |journal=Biogeosciences |volume=18 |issue=17 |pages=4937–4952 | doi=10.5194/bg-18-4937-2021|bibcode=2021BGeo...18.4937M |doi-access=free }}</ref> However, neither study was able to take abrupt thaw into account. In 2020, a study of the northern permafrost peatlands (a smaller subset of the entire permafrost area, covering 3.7 million km² out of the estimated 18 million km²<ref name=":4">{{Cite journal|last1=Sayedi|first1=Sayedeh Sara|last2=Abbott|first2=Benjamin W|last3=Thornton|first3=Brett F|last4=Frederick|first4=Jennifer M|last5=Vonk|first5=Jorien E|last6=Overduin|first6=Paul|last7=Schädel|first7=Christina|last8=Schuur|first8=Edward A G|last9=Bourbonnais|first9=Annie|last10=Demidov|first10=Nikita|last11=Gavrilov|first11=Anatoly|date=2020-12-01|title=Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment|journal=Environmental Research Letters|volume=15|issue=12|pages=B027-08|doi=10.1088/1748-9326/abcc29|bibcode=2020AGUFMB027...08S|s2cid=234515282|issn=1748-9326|doi-access=free}}</ref>) would amount to ~1% of anthropogenic [[radiative forcing]] by 2100, and that this proportion remains the same in all warming scenarios considered, from {{convert|1.5|C-change|F-change}} to {{convert|6|C-change|F-change}}. It had further suggested that after 200 more years, those peatlands would have absorbed more carbon than what they had emitted into the atmosphere.<ref name="Hugelius2020">{{Cite journal |last1=Hugelius |first1=Gustaf |last2=Loisel |first2=Julie |last3=Chadburn |first3=Sarah |display-authors=etal |date=10 August 2020 |title=Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw |journal= Proceedings of the National Academy of Sciences|volume=117 |issue=34 |pages=20438–20446 |doi=10.1073/pnas.1916387117|pmid=32778585 |pmc=7456150 |bibcode=2020PNAS..11720438H |doi-access=free }}</ref> The [[IPCC Sixth Assessment Report]] estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per {{convert|1|C-change|F-change}} of warming.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} For comparison, by 2019, ''annual'' anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} [[File:Schuur_2022_century-scale_permafrost_projections.jpeg|thumb|Nine probable scenarios of [[greenhouse gas emission]]s from permafrost thaw during the 21st century, which show a limited, moderate and intense {{CO2}} and {{CH4}} emission response to low, medium and high-emission [[Representative Concentration Pathway]]s. The vertical bar uses emissions of selected large countries as a comparison: the right-hand side of the scale shows their cumulative emissions since the start of the [[Industrial Revolution]], while the left-hand side shows each country's cumulative emissions for the rest of the 21st century if they remained unchanged from their 2019 levels.<ref name="Schuur2022" />]] A 2021 assessment of the economic impact of climate tipping points estimated that permafrost carbon emissions would increase the [[social cost of carbon]] by about 8.4% <ref>{{Cite journal |last1=Dietz |first1=Simon |last2=Rising |first2=James |last3=Stoerk |first3=Thomas |last4=Wagner |first4=Gernot |date=24 August 2021 |title=Economic impacts of tipping points in the climate system |journal=[[Proceedings of the National Academy of Sciences]] |volume=118 |issue=34 |pages=e2103081118|doi=10.1073/pnas.2103081118 |pmid=34400500 |pmc=8403967 |bibcode=2021PNAS..11803081D |doi-access=free }}</ref> However, the methods of that assessment have attracted controversy: when researchers like [[Steve Keen]] and [[Timothy Lenton]] had accused it of underestimating the overall impact of tipping points and of higher levels of warming in general,<ref>{{Cite journal |last1=Keen |first1=Steve |last2=Lenton |first2=Timothy M. |last3=Garrett |first3=Timothy J. |last4=Rae |first4=James W. B. |last5=Hanley |first5=Brian P. |last6=Grasselli |first6=Matheus |date=19 May 2022 |title=Estimates of economic and environmental damages from tipping points cannot be reconciled with the scientific literature |journal=Proceedings of the National Academy of Sciences |volume=119 |issue=21 |pages=e2117308119 |doi=10.1073/pnas.2117308119 |doi-access=free |pmid=35588449 |pmc=9173761 |bibcode=2022PNAS..11917308K |s2cid=248917625 }}</ref> the authors have conceded some of their points.<ref>{{Cite journal |last1=Dietz |first1=Simon |last2=Rising |first2=James |last3=Stoerk |first3=Thomas |last4=Wagner |first4=Gernot |date=19 May 2022 |title=Reply to Keen et al.: Dietz et al. modeling of climate tipping points is informative even if estimates are a probable lower bound |journal=Proceedings of the National Academy of Sciences |volume=119 |issue=21 |pages= e2201191119 |doi=10.1073/pnas.2201191119 |doi-access=free |pmid=35588452 |pmc=9173815 |bibcode=2022PNAS..11901191D }}</ref> In 2021, a group of prominent permafrost researchers like [[Merritt Turetsky]] had presented their collective estimate of permafrost emissions, including the abrupt thaw processes, as part of an effort to advocate for a 50% reduction in anthropogenic emissions by 2030 as a necessary milestone to help reach net zero by 2050. Their figures for combined permafrost emissions by 2100 amounted to 150–200 billion tonnes of carbon dioxide equivalent under {{convert|1.5|C-change|F-change}} of warming, 220–300 billion tonnes under {{convert|2|C-change|F-change}} and 400–500 billion tonnes if the warming was allowed to exceed {{convert|4|C-change|F-change}}. They compared those figures to the extrapolated present-day emissions of [[Canada]], the [[European Union]] and the [[United States]] or [[China]], respectively. The 400–500 billion tonnes figure would also be equivalent to the today's remaining budget for staying within a {{convert|1.5|C-change|F-change}} target.<ref>{{cite web |date=2021 |title=Carbon Emissions from Permafrost |url=https://www.50x30.net/carbon-emissions-from-permafrost |language=en |website=50x30 |access-date=8 October 2022}}</ref> One of the scientists involved in that effort, [[Susan M. Natali]] of [[Woods Hole Research Centre]], had also led the publication of a complementary estimate in a [[PNAS]] paper that year, which suggested that when the amplification of permafrost emissions by abrupt thaw and wildfires is combined with the foreseeable range of near-future anthropogenic emissions, avoiding the exceedance (or "overshoot") of {{convert|1.5|C-change|F-change}} warming is already implausible, and the efforts to attain it may have to rely on [[carbon dioxide removal|negative emissions]] to force the temperature back down.<ref>{{Cite journal |last1=Natali |first1=Susan M. |last2=Holdren |first2=John P. |last3=Rogers |first3=Brendan M. |last4=Treharne |first4=Rachael |last5=Duffy |first5=Philip B. |last6=Pomerance |first6=Rafe |last7=MacDonald |first7=Erin |date=10 December 2020 |title=Permafrost carbon feedbacks threaten global climate goals |journal=Biological Sciences |volume=118 |issue=21 |doi=10.1073/pnas.2100163118|pmid=34001617 |pmc=8166174 |doi-access=free }}</ref> An updated 2022 assessment of climate tipping points concluded that abrupt permafrost thaw would add 50% to gradual thaw rates, and would add 14 billion tons of carbon dioxide equivalent emissions by 2100 and 35 billion tons by 2300 per every degree of warming. This would have a warming impact of {{convert|0.04|C-change|F-change}} per every full degree of warming by 2100, and {{convert|0.11|C-change|F-change}} per every full degree of warming by 2300. It also suggested that at between {{convert|3|C-change|F-change}} and {{convert|6|C-change|F-change}} degrees of warming (with the most likely figure around {{convert|4|C-change|F-change}} degrees) a large-scale collapse of permafrost areas could become irreversible, adding between 175 and 350 billion tons of {{chem2|CO2}} equivalent emissions, or {{convert|0.2-0.4|C-change|F-change}} degrees, over about 50 years (with a range between 10 and 300 years).<ref>{{Cite journal |last1=Armstrong McKay |first1=David|last2=Abrams |first2=Jesse |last3=Winkelmann |first3=Ricarda |last4=Sakschewski |first4=Boris |last5=Loriani |first5=Sina |last6=Fetzer |first6=Ingo|last7=Cornell|first7=Sarah |last8=Rockström |first8=Johan |last9=Staal |first9=Arie |last10=Lenton |first10=Timothy |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=Science |language=en |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><ref>{{Cite web |last=Armstrong McKay |first=David |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer |url=https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/ |access-date=2 October 2022 |website=climatetippingpoints.info |language=en}}</ref> A major review published in the year 2022 concluded that if the goal of preventing {{convert|2|C-change|F-change}} of warming was realized, then the average annual permafrost emissions throughout the 21st century would be equivalent to the year 2019 annual emissions of [[Russia]]. Under RCP4.5, a scenario considered close to the current trajectory and where the warming stays slightly below {{convert|3|C-change|F-change}}, annual permafrost emissions would be comparable to year 2019 emissions of [[Western Europe]] or the [[United States]], while under the scenario of high global warming and worst-case permafrost feedback response, they would nearly match year 2019 emissions of [[China]].<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 }}</ref> ==See also== * [[Fire and carbon cycling in boreal forests]] * [[Carbon cycle]] ==References== {{reflist|30em}} ==External links== * [http://ipa.arcticportal.org/ International Permafrost Association] * [http://cenperm.ku.dk// Center for Permafrost] * [https://web.archive.org/web/20101124144710/http://science.nasa.gov/missions/carve/ Carbon in Arctic Reservoirs Vulnerability Experiment] {{Global Warming}} {{DEFAULTSORT:Permafrost Carbon Cycle}} [[Category:Climate change feedbacks]] [[Category:Carbon cycle]] [[Category:Permafrost]]'

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'{{Short description|Sub-cycle of the larger global carbon cycle}} {{Use dmy dates|date=September 2019}} {{About|movement of carbon in and around permafrost|other aspects of permafrost|permafrost}} [[File:Schuur_2022_permafrost_carbon_literature.jpeg|thumb|The annual number of scientific research papers published on the subject of permafrost carbon has grown from next to nothing around 1990 to around 400 by 2020.<ref name="Schuur2022" /> ]] {{Carbon cycle|By regions}} The '''permafrost carbon cycle''' or '''Arctic carbon cycle''' is a sub-cycle of the larger global [[carbon cycle]]. [[Permafrost]] is defined as subsurface material that remains below 0^o C (32^o F) for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir, one which was often neglected in the initial research determining global terrestrial carbon reservoirs. Since the start of the 2000s, however, far more attention has been paid to the subject,<ref name=zimov>{{Cite journal|vauthors=Zimov SA, Schuur EA, Chapin FS |title=Climate change. Permafrost and the global carbon budget |journal=Science |volume=312 |issue=5780 |pages=1612–3 |date=June 2006 |pmid=16778046 |doi=10.1126/science.1128908 |s2cid=129667039 }}</ref> with an enormous growth both in general attention and in the scientific research output.<ref name="Schuur2022" /> The permafrost carbon cycle deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to [[Atmosphere of Earth|the atmosphere]], back to vegetation, and, finally, back to permafrost soils through burial and sedimentation due to cryogenic processes. Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle. The cycle includes the exchange of [[carbon dioxide]] and [[methane]] between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water as methane, [[dissolved organic carbon]], [[dissolved inorganic carbon]], [[particulate inorganic carbon]], and [[particulate organic carbon]].<ref>{{Cite journal|doi=10.1890/08-2025.1 |author=McGuire, A.D., Anderson, L.G., Christensen, T.R., Dallimore, S., Guo, L., Hayes, D.J., Heimann, M., Lorenson, T.D., Macdonald, R.W., and Roulet, N. |title=Sensitivity of the carbon cycle in the Arctic to climate change |journal=Ecological Monographs |volume=79 |issue=4 |pages=523–555 |year=2009 |bibcode=2009EcoM...79..523M |hdl=11858/00-001M-0000-000E-D87B-C |s2cid=1779296 |hdl-access=free }}</ref> ==Storage== Soils, in general, are the largest reservoirs of carbon in [[Ecosystem|terrestrial ecosystem]]s. This is also true for soils in the Arctic that are underlain by permafrost. In 2003, Tarnocai, et al. used the Northern and Mid Latitudes Soil Database to make a determination of carbon stocks in [[Gelisols|cryosols]]—soils containing permafrost within two meters of the soil surface.<ref name=kimble>{{Cite book|author=Tarnocai, C., Kimble, J., Broll, G. |chapter=Determining carbon stocks in Cryosols using the Northern and Mid Latitudes Soil Database |chapter-url=http://www.arlis.org/docs/vol1/ICOP/55700698/Pdf/Chapter_198.pdf |editor1=Phillips, Marcia |editor2=Springman, Sarah M |editor3=Arenson, Lukas U |title=Permafrost: Proceedings of the 8th International Conference on Permafrost, Zurich, Switzerland, 21–25 July 2003 |pages=1129–34 |publisher=Momenta |year=2003 |location=London |isbn=978-90-5809-584-8}}</ref> Permafrost affected soils cover nearly 9% of the Earth's land area, yet store between 25 and 50% of the soil organic carbon. These estimates show that permafrost soils are an important carbon pool.<ref name=bockheim>{{Cite journal |doi=10.2136/sssaj2007.0070N |author1=Bockheim, J.G. |author2=Hinkel, K.M. |name-list-style=amp |title=The importance of "Deep" organic carbon in permafrost-affected soils of Arctic Alaska |journal=Soil Science Society of America Journal |volume=71 |issue=6 |pages=1889–92 |year=2007 |url=http://soil.scijournals.org/cgi/content/abstract/71/6/1889 |bibcode=2007SSASJ..71.1889B |access-date=5 June 2010 |archive-url=https://web.archive.org/web/20090717063627/http://soil.scijournals.org/cgi/content/abstract/71/6/1889 |archive-date=17 July 2009 }}</ref> These soils not only contain large amounts of carbon, but also sequester carbon through [[cryoturbation]] and cryogenic processes.<ref name=kimble/><ref name=tarnocai/> ===Processes=== Carbon is not produced by permafrost. Organic carbon derived from terrestrial vegetation must be incorporated into the soil column and subsequently be incorporated into permafrost to be effectively stored. Because permafrost responds to climate changes slowly, carbon storage removes carbon from the atmosphere for long periods of time. [[Radiocarbon]] dating techniques reveal that carbon within permafrost is often thousands of years old.<ref name=guo/><ref name=nowinski/> Carbon storage in permafrost is the result of two primary processes. *The first process that captures carbon and stores it is [[syngenetic permafrost growth]].<ref>{{Cite journal|last1=Anderson|first1=D. A.|last2=Bray|first2=M. T.|last3=French|first3=H. M.|last4=Shur|first4=Y.|date=1 October 2004|title=Syngenetic permafrost growth: cryostratigraphic observations from the CRREL tunnel near Fairbanks, Alaska|journal=Permafrost and Periglacial Processes|language=en|volume=15|issue=4|pages=339–347|doi=10.1002/ppp.486|bibcode=2004PPPr...15..339S |s2cid=128478370 |issn=1099-1530}}</ref> This process is the result of a constant active layer where thickness and energy exchange between permafrost, active layer, biosphere, and atmosphere, resulting in the vertical increase of the soil surface elevation. This aggradation of soil is the result of [[Aeolian processes|aeolian]] or [[fluvial]] sedimentation and/or [[peat]] formation. Peat accumulation rates are as high as 0.5mm/yr while sedimentation may cause a rise of 0.7mm/yr. Thick silt deposits resulting from abundant loess deposition during the [[last glacial maximum]] form thick carbon-rich soils known as [[yedoma]].<ref name=schuur/> As this process occurs, the organic and mineral soil that is deposited is incorporated into the permafrost as the permafrost surface rises. *The second process responsible for storing carbon is [[cryoturbation]], the mixing of soil due to freeze-thaw cycles. Cryoturbation moves carbon from the surface to depths within the soil profile. [[Frost heaving]] is the most common form of cryoturbation. Eventually, carbon that originates at the surface moves deep enough into the active layer to be incorporated into permafrost. When cryoturbation and the deposition of sediments act together carbon storage rates increase.<ref name=schuur/> ===Current estimates=== [[File:Hugelius_2020_peatland_projections.jpg|thumb|Permafrost peatlands under varying extent of global warming, and the resultant emissions as a fraction of anthropogenic emissions needed to cause that extent of warming.<ref name="Hugelius2020" />]] It is estimated that the total soil organic carbon (SOC) stock in northern circumpolar permafrost region equals around 1,460–1,600 [[Kilogram#SI multiples|Pg]].<ref name=tarnocai>{{Cite journal |author=Tarnocai, C., Canadell, J.G., Schuur, E.A.G., Kuhry, P., Mazhitova, G., and Zimov, S. |title=Soil organic carbon pools in the northern circumpolar permafrost region |journal=Global Biogeochemical Cycles |volume=23 |issue=2 |year=2009 |pages=GB2023 |doi=10.1029/2008GB003327 |bibcode=2009GBioC..23.2023T |doi-access=free }}</ref> (1 Pg = 1 Gt = 10¹⁵g)<ref>{{Cite journal|last1=Hugelius|first1=G.|last2=Strauss|first2=J.|last3=Zubrzycki|first3=S.|last4=Harden|first4=J. W.|author-link4=Jennifer Harden|last5=Schuur|first5=E. A. G.|last6=Ping|first6=C.-L.|last7=Schirrmeister|first7=L.|last8=Grosse|first8=G.|last9=Michaelson|first9=G. J.|last10=Koven|first10=C. D.|last11=O'Donnell|first11=J. A.|date=2014-12-01|title=Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps|journal=Biogeosciences|volume=11|issue=23|pages=6573–6593|doi=10.5194/bg-11-6573-2014|bibcode=2014BGeo...11.6573H|s2cid=14158339 |issn=1726-4189|doi-access=free}}</ref><ref name="ARC2019">{{Cite web|title=Permafrost and the Global Carbon Cycle|url=https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/844/Permafrost-and-the-Global-Carbon-Cycle|access-date=2021-05-18|website=Arctic Program|date=31 October 2019 |language=en-US}}</ref> With the [[Tibetan Plateau]] carbon content included, the total carbon pools in the permafrost of the Northern Hemisphere is likely to be around 1832 Gt.<ref>{{cite journal |last1=Mu |first1=C. |last2=Zhang |first2=T. |last3=Wu |first3=Q. |last4=Peng |first4=X. |last5=Cao |first5=B. |last6=Zhang |first6=X. |last7=Cao |first7=B. |last8=Cheng |first8=G. |title=Editorial: Organic carbon pools in permafrost regions on the Qinghai–Xizang (Tibetan) Plateau |journal=The Cryosphere |date=6 March 2015 |volume=9 |issue=2 |pages=479–486 |doi=10.5194/tc-9-479-2015 |bibcode=2015TCry....9..479M |url=https://tc.copernicus.org/articles/9/479/2015/tc-9-479-2015.pdf |access-date=5 December 2022 |doi-access=free }}</ref> This estimation of the amount of carbon stored in permafrost soils is more than double the amount currently in the atmosphere.<ref name=zimov/> Soil column in the permafrost soils is generally broken into three horizons, 0–30&nbsp;cm, 0–100&nbsp;cm, and 1–300&nbsp;cm. The uppermost horizon (0–30&nbsp;cm) contains approximately 200 Pg of organic carbon. The 0–100&nbsp;cm horizon contains an estimated 500 Pg of organic carbon, and the 0–300&nbsp;cm horizon contains an estimated 1024 Pg of organic carbon. These estimates more than doubled the previously known carbon pools in permafrost soils.<ref name=kimble/><ref name=bockheim/><ref name=tarnocai/> Additional carbon stocks exist in [[yedoma]] (400 Pg), carbon rich [[loess]] deposits found throughout Siberia and isolated regions of North America, and deltaic deposits (240 Pg) throughout the Arctic. These deposits are generally deeper than the 3 m investigated in traditional studies.<ref name=tarnocai/> Many concerns arise because of the large amount of carbon stored in permafrost soils. Until recently, the amount of carbon present in permafrost was not taken into account in climate models and global carbon budgets.<ref name=zimov/><ref name=schuur/> ==Carbon release from the permafrost== Carbon is continually cycling between soils, vegetation, and the atmosphere. As climate change increases mean annual air temperatures throughout the Arctic, it extends permafrost thaw and deepens the active layer, exposing old carbon that has been in storage for decades to millennia to biogenic processes which facilitate its entrance into the atmosphere. In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per {{convert|1|C-change|F-change}}of global warming.<ref name="AR6_WG1_Chapter922">Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G.  Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf Chapter 9: Ocean, Cryosphere and Sea Level Change]. 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, NY, USA, pp. 1211–1362, doi:10.1017/9781009157896.011.</ref>{{rp|1283}} According to the [[IPCC Sixth Assessment Report]], there is high confidence that global warming over the last few decades has led to widespread increases in permafrost temperature.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} Observed warming was up to {{convert|3|C-change|F-change}} in parts of Northern Alaska (early 1980s to mid-2000s) and up to {{convert|2|C-change|F-change}} in parts of the Russian European North (1970–2020), and active layer thickness has increased in the European and Russian Arctic across the 21st century and at high elevation areas in Europe and Asia since the 1990s.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} In [[Yukon]], the zone of continuous permafrost might have moved {{convert|100|km}} poleward since 1899, but accurate records only go back 30 years. Based on high agreement across model projections, fundamental process understanding, and paleoclimate evidence, it is virtually certain that permafrost extent and volume will continue to shrink as global climate warms.<ref name="AR6_WG1_Chapter922" />{{rp|1283}} [[File:Douglas_2020_precipitation_layers.png|thumb|left|Greater summer precipitation increases the depth of permafrost layer subject to thaw, in different Arctic permafrost environments.<ref name="Douglas2020" />]] Carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it a [[Climate change feedback#Positive feedbacks|positive climate change feedback]]. The warming also intensifies Arctic [[water cycle]], and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.<ref name="Douglas2020">{{Cite journal |last1=Douglas |first1=Thomas A. |last2=Turetsky |first2=Merritt R. |last3=Koven |first3=Charles D. |date=24 July 2020 |title=Increased rainfall stimulates permafrost thaw across a variety of Interior Alaskan boreal ecosystems |journal=npj Climate and Atmospheric Science |volume=3 |issue=1 |page=5626 |doi=10.1038/s41612-020-0130-4 |doi-access=free |bibcode=2020npCAS...3...28D }}</ref> The amount of carbon that will be released from warming conditions depends on depth of thaw, carbon content within the thawed soil, physical changes to the environment<ref name=nowinski>{{Cite journal|vauthors=Nowinski NS, Taneva L, [[Susan Trumbore|Trumbore SE]], Welker JM |title=Decomposition of old organic matter as a result of deeper active layers in a snow depth manipulation experiment |journal=Oecologia |volume=163 |issue=3 |pages=785–92 |date=January 2010 |pmid=20084398 |pmc=2886135 |doi=10.1007/s00442-009-1556-x |bibcode=2010Oecol.163..785N }}</ref> and microbial and vegetation activity in the soil. Microbial respiration is the primary process through which old permafrost carbon is re-activated and enters the atmosphere. The rate of microbial decomposition within organic soils, including thawed permafrost, depends on environmental controls, such as soil temperature, moisture availability, nutrient availability, and oxygen availability.<ref name=schuur>{{Cite journal|author=Schuur, E.A.G., Bockheim, J., Canadell, J.G., Euskirchen, E., Field, C.B., Goryachkin, S.V., Hagemann, S., Kuhry, P., Lafleur, P.M., Lee, H., Mazhitova, G., Nelson, F.E., Rinke, A., Romanovsky, V.E., Skiklomanov, N., Tarnocai, C., Venevsky, S., Vogel, J.G., and Zimov, S.A. |title=Vulnerability of Permafrost Carbon to Climate Change: Implications for the Global Carbon Cycle |journal=BioScience |volume=58 |issue=8 |pages=701–714 |year=2008 |doi=10.1641/B580807 |doi-access=free }}</ref> In particular, sufficient concentrations of iron oxides in some permafrost soils can inhibit microbial respiration and prevent carbon mobilization: however, this protection only lasts until carbon is separated from the iron oxides by Fe-reducing bacteria, which is only a matter of time under the typical conditions.<ref>{{Cite journal |last1=Lim |first1=Artem G. |last2=Loiko |first2=Sergey V. |last3=Pokrovsky |first3=Oleg S. |date=10 January 2023 |title=Interactions between organic matter and Fe oxides at soil micro-interfaces: Quantification, associations, and influencing factors |journal=Science of the Total Environment |volume=3 |page=158710 |doi=10.1016/j.scitotenv.2022.158710|pmid=36099954 |s2cid=252221350 |doi-access=free }}</ref> Depending on the soil type, [[Iron(III) oxide]] can boost oxidation of methane to carbon dioxide in the soil, but it can also amplify methane production by acetotrophs: these soil processes are not yet fully understood.<ref>{{Cite journal |last1=Patzner |first1=Monique S. |last2=Mueller |first2=Carsten W. |last3=Malusova |first3=Miroslava |last4=Baur |first4=Moritz |last5=Nikeleit |first5=Verena |last6=Scholten |first6=Thomas |last7=Hoeschen |first7=Carmen |last8=Byrne |first8=James M. |last9=Borch |first9=Thomas |last10=Kappler |first10=Andreas |last11=Bryce |first11=Casey |date=10 December 2020 |title=Iron mineral dissolution releases iron and associated organic carbon during permafrost thaw |journal=Nature Communications |volume=11 |issue=1 |page=6329 |doi=10.1038/s41467-020-20102-6|pmid=33303752 |pmc=7729879 |bibcode=2020NatCo..11.6329P }}</ref> Altogether, the likelihood of the entire carbon pool mobilizing and entering the atmosphere is low despite the large volumes stored in the soil. Although temperatures will increase, this does not imply complete loss of permafrost and mobilization of the entire carbon pool. Much of the ground underlain by permafrost will remain frozen even if warming temperatures increase the thaw depth or increase thermokarsting and permafrost degradation.<ref name=bockheim/> Moreover, other elements such as [[iron]] and [[aluminum]] can [[adsorbtion|adsorb]] some of the mobilized [[soil carbon]] before it reaches the atmosphere, and they are particularly prominent in the mineral sand layers which often overlay permafrost.<ref>{{cite journal | doi=10.1016/j.geoderma.2021.115601 | title=Sizable pool of labile organic carbon in peat and mineral soils of permafrost peatlands, western Siberia | date=2022 | last1=Lim | first1=Artem G. | last2=Loiko | first2=Sergey V. | last3=Pokrovsky | first3=Oleg S. | journal=Geoderma | volume=409 | bibcode=2022Geode.409k5601L }}</ref> On the other hand, once the permafrost area thaws, it will not go back to being permafrost for centuries even if the temperature increase reversed, making it one of the best-known examples of [[tipping points in the climate system]]. A 1993 study suggested that while the tundra was a [[carbon sink]] until the end of the 1970s, it had already transitioned to a net carbon source by the time the study concluded.<ref name="Oechel1993">{{cite journal | first1=Walter C.|last1=Oechel|first2=Steven J. |last2=Hastings |first3=George |last3=Vourlrtis |first4=Mitchell |last4=Jenkins |first5=George |last5=Riechers |first6=Nancy|last6=Grulkelast|display-authors=4 | date = 1993 | title = Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source | journal = [[Nature (journal)|Nature]] | volume = 361 | issue = 6412 | pages = 520–523 | doi = 10.1038/361520a0 |bibcode=1993Natur.361..520O |s2cid=4339256}}</ref> The 2019 Arctic Report Card estimated that Arctic permafrost releases between 0.3 and 0.6 Pg C per year.<ref name="ARC2019" /> That same year, a study settled on the 0.6 Pg C figure, as the net difference between the annual emissions of 1,66 Pg C during the winter season (October–April), and the model-estimated vegetation carbon uptake of 1 Pg C during the growing season. It estimated that under [[Representative Concentration Pathway|RCP]] 8.5, a scenario of continually accelerating greenhouse gas emissions, winter {{CO2}} emissions from the northern permafrost domain would increase 41% by 2100. Under the "intermediate" scenario RCP 4.5, where greenhouse gas emissions peak and plateau within the next two decades, before gradually declining for the rest of the century (a rate of mitigation deeply insufficient to meet the [[Paris Agreement]] goals) permafrost carbon emissions would increase by 17%.<ref>{{Cite journal|last1=Natali|first1=Susan M.|last2=Watts|first2=Jennifer D.|last3=Rogers|first3=Brendan M.|last4=Potter|first4=Stefano|last5=Ludwig|first5=Sarah M.|last6=Selbmann|first6=Anne-Katrin|last7=Sullivan|first7=Patrick F.|last8=Abbott|first8=Benjamin W.|last9=Arndt|first9=Kyle A.|last10=Birch|first10=Leah|last11=Björkman|first11=Mats P.|date=2019-10-21|title=Large loss of CO2 in winter observed across the northern permafrost region|journal=Nature Climate Change|volume=9|issue=11|pages=852–857|doi=10.1038/s41558-019-0592-8|pmid=35069807|pmc=8781060|bibcode=2019NatCC...9..852N|hdl=10037/17795|s2cid=204812327|issn=1758-678X}}</ref> In 2022, this was challenged by a study which used a record of atmospheric observations between 1980 and 2017, and found that permafrost regions have been gaining carbon on net, as process-based models underestimated net CO₂ uptake in the permafrost regions and overestimated it in the forested regions, where increased respiration in response to warming offsets more of the gains than was previously understood.<ref name="Liu2022">{{Cite journal |last1=Liu |first1=Zhihua |last2=Kimball |first2=John S. |last3=Ballantyne |first3=Ashley P. |last4=Parazoo |first4=Nicholas C. |last5=Wang |first5=Wen J. |last6=Bastos |first6=Ana |last7=Madani |first7=Nima |last8=Natali |first8=Susan M. |last9=Watts |first9=Jennifer D. |last10=Rogers |first10=Brendan M. |last11=Ciais |first11=Philippe |last12=Yu |first12=Kailiang |last13=Virkkala |first13=Anna-Maria |last14=Chevallier |first14=Frederic |last15=Peters |first15=Wouter |last16=Patra |first16=Prabir K. |last17=Chandra |first17=Naveen |date=2019-10-21|title=Respiratory loss during late-growing season determines the net carbon dioxide sink in northern permafrost regions |journal=Nature Communications |volume=13 |issue=1 |page=5626 |doi=10.1038/s41467-022-33293-x|pmid=36163194 |pmc=9512808 }}</ref> Notably, estimates of carbon release alone do not fully represent the impact of permafrost thaw on climate change. This is because carbon can either be released as carbon dioxide (CO₂) or methane (CH₄). [[Aerobic respiration]] releases carbon dioxide, while [[anaerobic respiration]] releases methane. This is a substantial difference, as while biogenic methane lasts less than 12 years in the atmosphere, its [[global warming potential]] is around 80 times larger than that of CO₂ over a 20-year period and between 28 and 40 times larger over a 100-year period.<ref>{{Cite book |last1=Forster |first1=Piers |title={{Harvnb|IPCC AR6 WG1|2021}} |last2=Storelvmo |first2=Trude |year=2021 |chapter=Chapter 7: The Earth's Energy Budget, Climate Feedbacks, and Climate Sensitivity |ref={{harvid|IPCC AR6 WG1 Ch7|2021}} |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter07.pdf}}</ref><ref>{{Cite journal |last1=Allen |first1=Robert J. |last2=Zhao |first2=Xueying |last3=Randles |first3=Cynthia A. |last4=Kramer |first4=Ryan J. |last5=Samset |first5=Bjørn H. |last6=Smith |first6=Christopher J. |date=16 March 2023 |title=Surface warming and wetting due to methane's long-wave radiative effects muted by short-wave absorption |journal=Nature Geoscience |volume=16 |issue=4 |pages=314–320 |bibcode=2023NatGe..16..314A |doi=10.1038/s41561-023-01144-z |s2cid=257595431}}</ref> ===Carbon dioxide emissions=== [[File:Liu_2022_permafrost_tree_cover.png|thumb|Recent observations suggest that {{CO2}} absorption had been increasing at a faster rate over the areas with a lot of permafrost and limited tree cover than over the areas with extensive tree cover.<ref name="Liu2022" />]] Most of the permafrost soil are oxic and provide a suitable environment for aerobic microbial respiration. As such, carbon dioxide emissions account for the overwhelming majority of permafrost emissions and of the Arctic emissions in general.<ref>{{Cite journal |last1=Miner |first1=Kimberley R. |last2=Turetsky |first2=Merritt R. |last3=Malina |first3=Edward |last4=Bartsch |first4=Annett |last5=Tamminen |first5=Johanna |last6=McGuire |first6=A. David |last7=Fix |first7=Andreas |last8=Sweeney |first8=Colm |last9=Elder |first9=Clayton D. |last10=Miller |first10=Charles E. |date=11 January 2022|title=Permafrost carbon emissions in a changing Arctic |url=https://www.nature.com/articles/s43017-021-00230-3 |journal=Nature Reviews Earth & Environment |volume=13 |issue=1 |pages=55–67 |doi=10.1038/s43017-021-00230-3|bibcode=2022NRvEE...3...55M |s2cid=245917526 }}</ref> There's some debate over whether the observed emissions from permafrost soils primarily constitute microbial respiration of ancient carbon, or simply greater respiration of modern-day carbon (i.e. leaf litter), due to warmer soils intensifying microbial metabolism. Studies published in the early 2020s indicate that while soil microbiota still primarily consumes and respires modern carbon when plants grow during the spring and summer, these microorganisms then sustain themselves on ancient carbon during the winter, releasing it into the atmosphere.<ref>{{Cite journal |last1=Estop-Aragonés |first1= Cristian |last2=Olefeldt |first2=David |display-authors=etal |date=2 September 2020 |title=Assessing the Potential for Mobilization of Old Soil Carbon After Permafrost Thaw: A Synthesis of 14C Measurements From the Northern Permafrost Region |journal=Global Biogeochemical Cycles |volume=34 |issue=9 |doi=10.1029/2020GB006672|bibcode= 2020GBioC..3406672E |s2cid= 225258236 |doi-access=free }}</ref><ref>{{Cite journal |last1=Pedron |first1=Shawn A. |last2=Welker |first2=J. M. |last3=Euskirchen |first3=E. S. |last4=Klein |first4=E. S. |last5=Walker |first5=J. C. |last6=Xu |first6=X. |last7=Czimczik |first7=C. I. |date=14 March 2022 |title=Closing the Winter Gap—Year-Round Measurements of Soil CO2 Emission Sources in Arctic Tundra |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL097347 |journal=Geophysical Research Letters |volume=49 |issue=6 |doi=10.1029/2021GL097347|bibcode=2022GeoRL..4997347P |s2cid=247491567 }}</ref> On the other hand, former permafrost areas consistently see increased vegetation growth, or primary production, as plants can set down deeper roots in the thawed soil and grow larger and uptake more carbon. This is generally the main counteracting feedback on permafrost carbon emissions. However, in areas with streams and other waterways, more of their leaf litter enters those waterways, increasing their dissolved organic carbon content. Leaching of soil organic carbon from permafrost soils is also accelerated by warming climate and by erosion along river and stream banks freeing the carbon from the previously frozen soil.<ref name=guo>{{Cite journal|author=Guo, L., Chien-Lu Ping, and Macdonald, R.W. |title=Mobilization pathways of organic carbon from permafrost to arctic rivers in a changing climate |journal=Geophysical Research Letters |volume=34 |issue=13 |pages=L13603 |date=July 2007 |doi=10.1029/2007GL030689 |bibcode=2007GeoRL..3413603G|s2cid=129757480 }}</ref> Moreover, thawed areas become more vulnerable to wildfires, which alter landscape and release large quantities of stored organic carbon through combustion. As these fires burn, they remove organic matter from the surface. Removal of the protective organic mat that insulates the soil exposes the underlying soil and permafrost to increased [[solar radiation]], which in turn increases the soil temperature, active layer thickness, and changes soil moisture. Changes in the soil moisture and saturation alter the ratio of [[oxic]] to anoxic decomposition within the soil.<ref name=meyers>{{Cite journal|doi=10.1029/2007JG000423 |author=Meyers-Smith, I.H., McGuire, A.D., Harden, J.W., Chapin, F.S. |title=Influence of disturbance on carbon exchange in a permafrost collapse and adjacent burned forest |journal=Journal of Geophysical Research |volume=112 |issue=G4 |pages=G04017 |year=2007 |bibcode=2007JGRG..112.4017M|url=https://www.pure.ed.ac.uk/ws/files/8365805/PDF_Myers_Smith.et.al2007.pdf |doi-access=free }}</ref> A hypothesis promoted by [[Sergey Zimov]] is that the reduction of herds of large herbivores has increased the ratio of energy emission and energy absorption tundra (energy balance) in a manner that increases the tendency for net thawing of permafrost.<ref>{{cite web|title=Mammoth steppe: a high-productivity phenomenon|author=S.A. Zimov, N.S. Zimov, A.N. Tikhonov, [[F. Stuart Chapin III|F.S. Chapin III]]|url=http://www.lter.uaf.edu/pdf/1754_Zimov_Zimov_2012.pdf|year=2012|publisher=In: [[Quaternary Science Reviews]], vol.&nbsp;57, 4&nbsp;December&nbsp;2012, p.&nbsp;42&nbsp;fig.17|access-date=17 October 2014|archive-url=https://web.archive.org/web/20160304103247/http://www.lter.uaf.edu/pdf/1754_Zimov_Zimov_2012.pdf|archive-date=4 March 2016}}</ref> He is testing this hypothesis in an experiment at [[Pleistocene Park]], a nature reserve in northeastern Siberia.<ref>Sergey A. Zimov (6 May 2005): [https://www.science.org/doi/full/10.1126/science.1113442 "Pleistocene Park: Return of the Mammoth's Ecosystem."] {{Webarchive|url=https://web.archive.org/web/20170220222928/http://science.sciencemag.org/content/308/5723/796.1.full |date=2017-02-20 }} In: ''[[Science (journal)|Science]]'', pages 796–798. Article also to be found in [http://www.pleistocenepark.ru/en/materials/ www.pleistocenepark.ru/en/ – Materials.] {{Webarchive|url=https://web.archive.org/web/20161103172534/http://www.pleistocenepark.ru/en/materials/ |date=2016-11-03 }} Retrieved 5 May 2013.</ref> On the other hand, warming allows the [[beaver]]s to extend their habitat further north, where their [[Beaver dam#Effects|dams impair]] boat travel, impact access to food, affect water quality, and endanger downstream fish populations.<ref name=Guardian_20220104/> Pools formed by the dams store heat, thus changing local [[hydrology]] and causing localized permafrost thaw.<ref name=Guardian_20220104>{{cite news |last1=Milman |first1=Oliver |title=Dam it: beavers head north to the Arctic as tundra continues to heat up |url=https://www.theguardian.com/world/2022/jan/04/beavers-arctic-north-climate-crisis |newspaper=The Guardian |date=January 4, 2022 |archive-url=https://web.archive.org/web/20220104220623/https://www.theguardian.com/world/2022/jan/04/beavers-arctic-north-climate-crisis |archive-date=January 4, 2022 |url-status=live }}</ref> ===Methane emissions=== {{See also|Arctic methane emissions}} [[File:Bernhard_2022_RTS_activity.png|thumb|Carbon cycle accelerates in the wake of abrupt thaw (orange) relative to the previous state of the area (blue, black).<ref name="Bernhard2022" />]] Global warming in the Arctic accelerates methane release from both existing stores and [[methanogenesis]] in rotting [[Biomass (ecology)|biomass]].<ref>{{Cite journal| doi = 10.1029/2007JG000569| title = Methane production and bubble emissions from arctic lakes: Isotopic implications for source pathways and ages |year = 2008| last1 = Walter | first1 = K. M.| last2 = Chanton | first2 = J. P. |author-link2=Jeff Chanton| last3 = Chapin | first3 = F. S.| last4 = Schuur | first4 = E. A. G.| last5 = Zimov | first5 = S. A.| journal = Journal of Geophysical Research| volume = 113| issue = G3 | pages = G00A08 | bibcode=2008JGRG..113.0A08W| doi-access = free}}</ref> Methanogenesis requires thoroughly anaerobic environments, which slows down the mobilization of old carbon. A 2015 ''[[Nature (magazine)|Nature]]'' review estimated that the cumulative emissions from thawed anaerobic permafrost sites were 75–85% lower than the cumulative emissions from aerobic sites, and that even there, methane emissions amounted to only 3% to 7% of CO₂ emitted in situ. While they represented between 25% and 45% of the CO₂'s potential impact on climate over a 100-year timescale, the review concluded that aerobic permafrost thaw still had a greater warming impact overall.<ref>{{Cite journal|last1=Schuur |first1=E. A. G. |last2=McGuire |first2=A. D. |last3=Schädel |first3=C. |last4=Grosse |first4=G. |last5=Harden |first5=J. W. |display-authors=etal |date=9 April 2015|title=Climate change and the permafrost carbon feedback|url=https://www.nature.com/articles/nature14338 |journal=Nature |volume=520 |issue=7546 |pages=171–179 |doi=10.1038/nature14338|pmid=25855454 |bibcode=2015Natur.520..171S |hdl=1874/330256 |s2cid=4460926 }}</ref> In 2018, however, another study in ''[[Nature Climate Change]]'' performed seven-year incubation experiments and found that methane production became equivalent to CO₂ production once a methanogenic microbial community became established at the anaerobic site. This finding had substantially raised the overall warming impact represented by anaerobic thaw sites.<ref>{{Cite journal|last1=Pfeiffer|first1=Eva-Maria|last2=Grigoriev|first2=Mikhail N. |last3=Liebner |first3=Susanne |last4=Beer |first4=Christian |last5=Knoblauch|first5=Christian|date=April 2018|title=Methane production as key to the greenhouse gas budget of thawing permafrost|journal=Nature Climate Change|volume=8|issue=4|pages=309–312|doi=10.1038/s41558-018-0095-z|issn=1758-6798|bibcode=2018NatCC...8..309K|s2cid=90764924|url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:3094899}}</ref> Since methanogenesis requires anaerobic environments, it is frequently associated with Arctic lakes, where the emergence of bubbles of methane can be observed.<ref>{{cite journal|journal=Nature|volume=443|issue=7107|pages=71–75|date=7 September 2006| doi=10.1038/nature05040|pmid=16957728|title=Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming |first1=KM |last1=Walter |first2=SA |last2=Zimov |first3=JP |last3=Chanton |first4=D |last4=Verbyla |first5=FS III|last5=Chapin|display-authors=4|bibcode=2006Natur.443...71W|s2cid=4415304}}</ref><ref name="NYT Thaw">{{cite news|title=As Permafrost Thaws, Scientists Study the Risks|url=https://www.nytimes.com/2011/12/17/science/earth/warming-arctic-permafrost-fuels-climate-change-worries.html|access-date=December 17, 2011|newspaper=The New York Times|date=December 16, 2011|first=Justin|last=Gillis}}</ref> Lakes produced by the thaw of particularly ice-rich permafrost are known as [[thermokarst]] lakes. Not all of the methane produced in the sediment of a lake reaches the atmosphere, as it can get oxidized in the water column or even within the sediment itself:<ref>{{Cite journal |last1=Vigderovich |first1=Hanni |last2=Eckert |first2=Werner |last3=Elul |first3=Michal |last4=Rubin-Blum |first4=Maxim |last5=Elvert |first5=Marcus |last6=Sivan |first6=Orit |last7=Czimczik |first7=C. I. |date=2 May 2022 |title=Long-term incubations provide insight into the mechanisms of anaerobic oxidation of methane in methanogenic lake sediments |url=https://bg.copernicus.org/articles/19/2313/2022/ |journal=Biogeosciences |volume=19 |issue=8 |doi=10.1029/2021GL097347|bibcode=2022GeoRL..4997347P |s2cid=247491567 }}</ref> However, 2022 observations indicate that at least half of the methane produced within thermokarst lakes reaches the atmosphere.<ref>{{Cite journal |last1=Pellerin |first1=André |last2=Lotem |first2=Noam |last3=Anthony |first3=Katey Walter |last4=Russak |first4=Efrat Eliani |last5=Hasson |first5=Nicholas |last6=Røy |first6=Hans |last7=Chanton |first7=Jeffrey P. |last8=Sivan |first8=Orit |date=4 March 2022 |title=Methane production controls in a young thermokarst lake formed by abrupt permafrost thaw |journal=Global Change Biology |volume=28 |issue=10 |pages=3206–3221 |doi=10.1111/gcb.16151|pmid=35243729 |pmc=9310722 }}</ref> Another process which frequently results in substantial methane emissions is the [[erosion]] of permafrost-stabilized hillsides and their ultimate collapse.<ref>{{Cite journal|last=Turetsky|first=Merritt R.|date=2019-04-30|title=Permafrost collapse is accelerating carbon release|journal=Nature|volume=569|issue=7754|pages=32–34|bibcode=2019Natur.569...32T|doi=10.1038/d41586-019-01313-4|pmid=31040419|doi-access=free}}</ref> Altogether, these two processes - hillside collapse (also known as retrogressive thaw slump, or RTS) and thermokarst lake formation - are collectively described as abrupt thaw, as they can rapidly expose substantial volumes of soil to microbial respiration in a matter of days, as opposed to the gradual, cm by cm, thaw of formerly frozen soil which dominates across most permafrost environments. This rapidity was illustrated in 2019, when three permafrost sites which would have been safe from thawing under the "intermediate" [[Representative Concentration Pathway]] 4.5 for 70 more years had undergone abrupt thaw.<ref name="TGRomanovsky">{{Cite news|url=https://www.theguardian.com/environment/2019/jun/18/arctic-permafrost-canada-science-climate-crisis|title=Scientists shocked by Arctic permafrost thawing 70 years sooner than predicted|date=2019-06-18|work=The Guardian|access-date=2019-07-02|language=en-GB|issn=0261-3077}}</ref> Another example occurred in the wake of a 2020 Siberian heatwave, which was found to have increased RTS numbers 17-fold across the northern [[Taymyr Peninsula]] – from 82 to 1404, while the resultant soil carbon mobilization increased 28-fold, to an average of 11 grams of carbon per square meter per year across the peninsula (with a range between 5 and 38 grams).<ref name="Bernhard2022">{{Cite journal |last1=Bernhard |first1=Philipp |last2=Zwieback |first2=Simon |last3=Hajnsek |first3=Irena |date=2 May 2022 |title=Accelerated mobilization of organic carbon from retrogressive thaw slumps on the northern Taymyr Peninsula |url=https://tc.copernicus.org/articles/16/2819/2022/ |journal=The Cryosphere |volume= 16 |issue=7 |pages=2819–2835 |doi=10.5194/tc-16-2819-2022|bibcode=2022TCry...16.2819B |doi-access=free }}</ref> Until recently, Permafrost carbon feedback (PCF) modeling had mainly focused on gradual permafrost thaw, due to the difficulty of modelling abrupt thaw, and because of the flawed assumptions about the rates of methane production.<ref name=":5" /> Nevertheless, a study from 2018, by using field observations, radiocarbon dating, and remote sensing to account for [[thermokarst]] lakes, determined that abrupt thaw will more than double permafrost carbon emissions by 2100.<ref name=":6" /> And a second study from 2020, showed that under the scenario of continually accelerating emissions (RCP 8.5), abrupt thaw carbon emissions across 2.5 million km² are projected to provide the same feedback as gradual thaw of near-surface permafrost across the whole 18 million km² it occupies.<ref name=":5" /> Thus, abrupt thaw adds between 60 and 100 gigatonnes of carbon by 2300,<ref>{{Cite journal |vauthors=Turetsky MR, Abbott BW, Jones MC, Anthony KW, Olefeldt D, Schuur EA, Koven C, McGuire AD, Grosse G, Kuhry P, Hugelius G|date=May 2019 |title=Permafrost collapse is accelerating carbon release |journal=Nature |volume=569 |issue=7754 |pages=32–34 |doi=10.1038/d41586-019-01313-4|pmid=31040419 |bibcode=2019Natur.569...32T |doi-access=free }}</ref> increasing carbon emissions by ~125–190% when compared to gradual thaw alone.<ref name=":5">{{Cite journal|last1=Turetsky|first1=Merritt R.|last2=Abbott|first2=Benjamin W.|last3=Jones|first3=Miriam C.|last4=Anthony|first4=Katey Walter|last5=Olefeldt|first5=David|last6=Schuur|first6=Edward A. G.|last7=Grosse|first7=Guido|last8=Kuhry|first8=Peter|last9=Hugelius|first9=Gustaf|last10=Koven|first10=Charles|last11=Lawrence|first11=David M.|date=February 2020|title=Carbon release through abrupt permafrost thaw|journal=Nature Geoscience|volume=13|issue=2|pages=138–143|doi=10.1038/s41561-019-0526-0|bibcode=2020NatGe..13..138T|s2cid=213348269|issn=1752-0894}}</ref><ref name=":6">{{Cite journal|last1=Walter Anthony|first1=Katey|last2=Schneider von Deimling|first2=Thomas|last3=Nitze|first3=Ingmar|last4=Frolking|first4=Steve|last5=Emond|first5=Abraham|last6=Daanen|first6=Ronald|last7=Anthony|first7=Peter|last8=Lindgren|first8=Prajna|last9=Jones|first9=Benjamin|last10=Grosse|first10=Guido|date=2018-08-15|title=21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes|journal=Nature Communications|volume=9|issue=1|page=3262|doi=10.1038/s41467-018-05738-9|pmid=30111815|pmc=6093858|bibcode=2018NatCo...9.3262W|issn=2041-1723}}</ref> [[File:Hefferman_2022_bog_methane.png|thumb|left|Methane emissions from thawed permafrost appear to decrease as bog matures over time.<ref name="Heffernan2022" />]] However, there is still scientific debate about the rate and the trajectory of methane production in the thawed permafrost environments. For instance, a 2017 paper suggested that even in the thawing peatlands with frequent thermokarst lakes, less than 10% of methane emissions can be attributed to the old, thawed carbon, and the rest is anaerobic decomposition of modern carbon.<ref>{{Cite journal|last1=Cooper |first1=M. |last2=Estop-Aragonés |first2=C. |last3=Fisher |first3=J. |display-authors=etal|date=26 June 2017 |title=Limited contribution of permafrost carbon to methane release from thawing peatlands|url=https://www.nature.com/articles/nature14338 |journal=Nature Climate Change |volume=7 |issue=7 |pages=507–511 |doi=10.1038/nclimate3328|bibcode=2017NatCC...7..507C }}</ref> A follow-up study in 2018 had even suggested that increased uptake of carbon due to rapid peat formation in the thermokarst wetlands would compensate for the increased methane release.<ref>{{Cite journal |last1=Estop-Aragonés |first1=Cristian |last2=Cooper |first2=Mark D.A. |last3=Fisher |first3=James P. |display-authors=etal |date=March 2018 |title=Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands |journal=Soil Biology and Biochemistry |volume=118 |pages=115–129 |doi=10.1016/j.soilbio.2017.12.010|doi-access=free |bibcode=2018SBiBi.118..115E }}</ref> Another 2018 paper suggested that permafrost emissions are limited following thermokarst thaw, but are substantially greater in the aftermath of wildfires.<ref>{{Cite journal |last1=Estop-Aragonés |first1=Cristian |display-authors=etal|date=13 August 2018 |title=Respiration of aged soil carbon during fall in permafrost peatlands enhanced by active layer deepening following wildfire but limited following thermokarst |journal=Environmental Research Letters |volume=13 |issue=8 |page=085002 |doi=10.1088/1748-9326/aad5f0|bibcode=2018ERL....13h5002E |s2cid=158857491 |doi-access=free }}</ref> In 2022, a paper demonstrated that peatland methane emissions from permafrost thaw are initially quite high (82 milligrams of methane per square meter per day), but decline by nearly three times as the permafrost bog matures, suggesting a reduction in methane emissions in several decades to a century following abrupt thaw.<ref name="Heffernan2022">{{Cite journal|last1=Heffernan|first1=Liam |last2=Cavaco |first2= Maria A. |last3=Bhatia |first3=Maya P. |last4=Estop-Aragonés |first4= Cristian |last5=Knorr |first5=Klaus-Holger |last6=Olefeldt |first6=David |date=24 June 2022 |title=High peatland methane emissions following permafrost thaw: enhanced acetoclastic methanogenesis during early successional stages |url=https://bg.copernicus.org/articles/19/3051/2022/ |journal=Biogeosciences |volume=19 |issue=8 |pages=3051–3071 |doi=10.5194/bg-19-3051-2022|bibcode=2022BGeo...19.3051H |doi-access=free }}</ref> ===Subsea permafrost=== [[File:Sayedi_2020_subsea_projections.jpg|thumb|Carbon dioxide and methane (in {{CO2}} equivalent) emissions from subsea permafrost alone under the different [[Representative Concentration Pathway]] scenarios over time.<ref name=":4" />]] Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions.<ref>{{cite web|author=IPCC AR4|title=Climate Change 2007: Working Group I: The Physical Science Basis|date=2007|url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-7-2-4.html|access-date=12 April 2014|archive-url=https://web.archive.org/web/20140413125748/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-7-2-4.html|archive-date=13 April 2014}}</ref> Thus, it can be defined as "the unglaciated continental shelf areas exposed during the [[Last Glacial Maximum]] (LGM, ~26 500 BP) that are currently inundated". Large stocks of organic matter (OM) and methane ({{CH4}}) are accumulated below and within the subsea permafrost deposits.This source of methane is different from [[methane clathrate]]s, but contributes to the overall outcome and feedbacks in the Earth's climate system.<ref name=":4" /> The size of today's subsea permafrost has been estimated at 2 million km² (~1/5 of the terrestrial permafrost domain size), which constitutes a 30–50% reduction since the LGM. Containing around 560 GtC in OM and 45 GtC in CH₄, with a current release of 18 and 38 MtC per year respectively, which is due to the warming and thawing that the subsea permafrost domain has been experiencing since after the LGM (~14000 years ago). In fact, because the subsea permafrost systems responds at millennial timescales to climate warming, the current carbon fluxes it is emitting to the water are in response to climatic changes occurring after the LGM. Therefore, human-driven climate change effects on subsea permafrost will only be seen hundreds or thousands of years from today. According to predictions under a business-as-usual emissions scenario [[RCP8.5|RCP 8.5]], by 2100, 43 GtC could be released from the subsea permafrost domain, and 190 GtC by the year 2300. Whereas for the low emissions scenario RCP 2.6, 30% less emissions are estimated. This constitutes a significant anthropogenic-driven acceleration of carbon release in the upcoming centuries.<ref name=":4" /> ===Cumulative=== In 2011, preliminary computer analyses suggested that permafrost emissions could be equivalent to around 15% of anthropogenic emissions.<ref>{{cite news |title=As Permafrost Thaws, Scientists Study the Risks |first=Justin |last=Gillis |newspaper=The New York Times |date=December 16, 2011 |url=https://www.nytimes.com/2011/12/17/science/earth/warming-arctic-permafrost-fuels-climate-change-worries.html?pagewanted=all |access-date=2017-02-11 |archive-url=https://web.archive.org/web/20170519052405/http://www.nytimes.com/2011/12/17/science/earth/warming-arctic-permafrost-fuels-climate-change-worries.html?pagewanted=all |archive-date=2017-05-19 |url-status=live }}</ref> A 2018 perspectives article discussing [[tipping points in the climate system]] activated around {{convert|2|C-change|F-change}} of global warming suggested that at this threshold, permafrost thaw would add a further {{convert|0.09|C-change|F-change}} to global temperatures by 2100, with a range of {{convert|0.04-0.16|C-change|F-change}}<ref>{{Cite journal |last1=Schellnhuber |first1=Hans Joachim |last2=Winkelmann |first2=Ricarda |last3=Scheffer |first3=Marten |last4=Lade |first4=Steven J. |last5=Fetzer |first5=Ingo |last6=Donges |first6=Jonathan F. |last7=Crucifix |first7=Michel |last8=Cornell |first8=Sarah E. |last9=Barnosky |first9=Anthony D. |author-link9=Anthony David Barnosky |date=2018 |title=Trajectories of the Earth System in the Anthropocene |journal=[[Proceedings of the National Academy of Sciences]] |volume=115 |issue=33 |pages=8252–8259 |bibcode=2018PNAS..115.8252S |doi=10.1073/pnas.1810141115 |issn=0027-8424 |pmc=6099852 |pmid=30082409 |doi-access=free}}</ref> In 2021, another study estimated that in a future where [[net zero|zero emissions]] were reached following an emission of a further 1000 Pg C into the atmosphere (a scenario where temperatures ordinarily stay stable after the last emission, or start to decline slowly) permafrost carbon would add {{convert|0.06|C-change|F-change}} (with a range of {{convert|0.02-0.14|C-change|F-change}}) 50 years after the last anthropogenic emission, {{convert|0.09|C-change|F-change}} ({{convert|0.04-0.21|C-change|F-change}}) 100 years later and {{convert|0.27|C-change|F-change}} ({{convert|0.12-0.49|C-change|F-change}}) 500 years later.<ref>{{Cite journal |last1=MacDougall |first1=Andrew H. |date=10 September 2021 |title=Estimated effect of the permafrost carbon feedback on the zero emissions commitment to climate change |journal=Biogeosciences |volume=18 |issue=17 |pages=4937–4952 | doi=10.5194/bg-18-4937-2021|bibcode=2021BGeo...18.4937M |doi-access=free }}</ref> However, neither study was able to take abrupt thaw into account. In 2020, a study of the northern permafrost peatlands (a smaller subset of the entire permafrost area, covering 3.7 million km² out of the estimated 18 million km²<ref name=":4">{{Cite journal|last1=Sayedi|first1=Sayedeh Sara|last2=Abbott|first2=Benjamin W|last3=Thornton|first3=Brett F|last4=Frederick|first4=Jennifer M|last5=Vonk|first5=Jorien E|last6=Overduin|first6=Paul|last7=Schädel|first7=Christina|last8=Schuur|first8=Edward A G|last9=Bourbonnais|first9=Annie|last10=Demidov|first10=Nikita|last11=Gavrilov|first11=Anatoly|date=2020-12-01|title=Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment|journal=Environmental Research Letters|volume=15|issue=12|pages=B027-08|doi=10.1088/1748-9326/abcc29|bibcode=2020AGUFMB027...08S|s2cid=234515282|issn=1748-9326|doi-access=free}}</ref>) would amount to ~1% of anthropogenic [[radiative forcing]] by 2100, and that this proportion remains the same in all warming scenarios considered, from {{convert|1.5|C-change|F-change}} to {{convert|6|C-change|F-change}}. It had further suggested that after 200 more years, those peatlands would have absorbed more carbon than what they had emitted into the atmosphere.<ref name="Hugelius2020">{{Cite journal |last1=Hugelius |first1=Gustaf |last2=Loisel |first2=Julie |last3=Chadburn |first3=Sarah |display-authors=etal |date=10 August 2020 |title=Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw |journal= Proceedings of the National Academy of Sciences|volume=117 |issue=34 |pages=20438–20446 |doi=10.1073/pnas.1916387117|pmid=32778585 |pmc=7456150 |bibcode=2020PNAS..11720438H |doi-access=free }}</ref> The [[IPCC Sixth Assessment Report]] estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per {{convert|1|C-change|F-change}} of warming.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} For comparison, by 2019, ''annual'' anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes.<ref name="AR6_WG1_Chapter922" />{{rp|1237}} [[File:Schuur_2022_century-scale_permafrost_projections.jpeg|thumb|Nine probable scenarios of [[greenhouse gas emission]]s from permafrost thaw during the 21st century, which show a limited, moderate and intense {{CO2}} and {{CH4}} emission response to low, medium and high-emission [[Representative Concentration Pathway]]s. The vertical bar uses emissions of selected large countries as a comparison: the right-hand side of the scale shows their cumulative emissions since the start of the [[Industrial Revolution]], while the left-hand side shows each country's cumulative emissions for the rest of the 21st century if they remained unchanged from their 2019 levels.<ref name="Schuur2022" />]] A 2021 assessment of the economic impact of climate tipping points estimated that permafrost carbon emissions would increase the [[social cost of carbon]] by about 8.4% <ref>{{Cite journal |last1=Dietz |first1=Simon |last2=Rising |first2=James |last3=Stoerk |first3=Thomas |last4=Wagner |first4=Gernot |date=24 August 2021 |title=Economic impacts of tipping points in the climate system |journal=[[Proceedings of the National Academy of Sciences]] |volume=118 |issue=34 |pages=e2103081118|doi=10.1073/pnas.2103081118 |pmid=34400500 |pmc=8403967 |bibcode=2021PNAS..11803081D |doi-access=free }}</ref> However, the methods of that assessment have attracted controversy: when researchers like [[Steve Keen]] and [[Timothy Lenton]] had accused it of underestimating the overall impact of tipping points and of higher levels of warming in general,<ref>{{Cite journal |last1=Keen |first1=Steve |last2=Lenton |first2=Timothy M. |last3=Garrett |first3=Timothy J. |last4=Rae |first4=James W. B. |last5=Hanley |first5=Brian P. |last6=Grasselli |first6=Matheus |date=19 May 2022 |title=Estimates of economic and environmental damages from tipping points cannot be reconciled with the scientific literature |journal=Proceedings of the National Academy of Sciences |volume=119 |issue=21 |pages=e2117308119 |doi=10.1073/pnas.2117308119 |doi-access=free |pmid=35588449 |pmc=9173761 |bibcode=2022PNAS..11917308K |s2cid=248917625 }}</ref> the authors have conceded some of their points.<ref>{{Cite journal |last1=Dietz |first1=Simon |last2=Rising |first2=James |last3=Stoerk |first3=Thomas |last4=Wagner |first4=Gernot |date=19 May 2022 |title=Reply to Keen et al.: Dietz et al. modeling of climate tipping points is informative even if estimates are a probable lower bound |journal=Proceedings of the National Academy of Sciences |volume=119 |issue=21 |pages= e2201191119 |doi=10.1073/pnas.2201191119 |doi-access=free |pmid=35588452 |pmc=9173815 |bibcode=2022PNAS..11901191D }}</ref> In 2021, a group of prominent permafrost researchers like [[Merritt Turetsky]] had presented their collective estimate of permafrost emissions, including the abrupt thaw processes, as part of an effort to advocate for a 50% reduction in anthropogenic emissions by 2030 as a necessary milestone to help reach net zero by 2050. Their figures for combined permafrost emissions by 2100 amounted to 150–200 billion tonnes of carbon dioxide equivalent under {{convert|1.5|C-change|F-change}} of warming, 220–300 billion tonnes under {{convert|2|C-change|F-change}} and 400–500 billion tonnes if the warming was allowed to exceed {{convert|4|C-change|F-change}}. They compared those figures to the extrapolated present-day emissions of [[Canada]], the [[European Union]] and the [[United States]] or [[China]], respectively. The 400–500 billion tonnes figure would also be equivalent to the today's remaining budget for staying within a {{convert|1.5|C-change|F-change}} target.<ref>{{cite web |date=2021 |title=Carbon Emissions from Permafrost |url=https://www.50x30.net/carbon-emissions-from-permafrost |language=en |website=50x30 |access-date=8 October 2022}}</ref> One of the scientists involved in that effort, [[Susan M. Natali]] of [[Woods Hole Research Centre]], had also led the publication of a complementary estimate in a [[PNAS]] paper that year, which suggested that when the amplification of permafrost emissions by abrupt thaw and wildfires is combined with the foreseeable range of near-future anthropogenic emissions, avoiding the exceedance (or "overshoot") of {{convert|1.5|C-change|F-change}} warming is already implausible, and the efforts to attain it may have to rely on [[carbon dioxide removal|negative emissions]] to force the temperature back down.<ref>{{Cite journal |last1=Natali |first1=Susan M. |last2=Holdren |first2=John P. |last3=Rogers |first3=Brendan M. |last4=Treharne |first4=Rachael |last5=Duffy |first5=Philip B. |last6=Pomerance |first6=Rafe |last7=MacDonald |first7=Erin |date=10 December 2020 |title=Permafrost carbon feedbacks threaten global climate goals |journal=Biological Sciences |volume=118 |issue=21 |doi=10.1073/pnas.2100163118|pmid=34001617 |pmc=8166174 |doi-access=free }}</ref> An updated 2022 assessment of climate tipping points concluded that abrupt permafrost thaw would add 50% to gradual thaw rates, and would add 14 billion tons of carbon dioxide equivalent emissions by 2100 and 35 billion tons by 2300 per every degree of warming. This would have a warming impact of {{convert|0.04|C-change|F-change}} per every full degree of warming by 2100, and {{convert|0.11|C-change|F-change}} per every full degree of warming by 2300. It also suggested that at between {{convert|3|C-change|F-change}} and {{convert|6|C-change|F-change}} degrees of warming (with the most likely figure around {{convert|4|C-change|F-change}} degrees) a large-scale collapse of permafrost areas could become irreversible, adding between 175 and 350 billion tons of {{chem2|CO2}} equivalent emissions, or {{convert|0.2-0.4|C-change|F-change}} degrees, over about 50 years (with a range between 10 and 300 years).<ref>{{Cite journal |last1=Armstrong McKay |first1=David|last2=Abrams |first2=Jesse |last3=Winkelmann |first3=Ricarda |last4=Sakschewski |first4=Boris |last5=Loriani |first5=Sina |last6=Fetzer |first6=Ingo|last7=Cornell|first7=Sarah |last8=Rockström |first8=Johan |last9=Staal |first9=Arie |last10=Lenton |first10=Timothy |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=Science |language=en |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><ref>{{Cite web |last=Armstrong McKay |first=David |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer |url=https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/ |access-date=2 October 2022 |website=climatetippingpoints.info |language=en}}</ref> A major review published in the year 2022 concluded that if the goal of preventing {{convert|2|C-change|F-change}} of warming was realized, then the average annual permafrost emissions throughout the 21st century would be equivalent to the year 2019 annual emissions of [[Russia]]. Under RCP4.5, a scenario considered close to the current trajectory and where the warming stays slightly below {{convert|3|C-change|F-change}}, annual permafrost emissions would be comparable to year 2019 emissions of [[Western Europe]] or the [[United States]], while under the scenario of high global warming and worst-case permafrost feedback response, they would nearly match year 2019 emissions of [[China]].<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 }}</ref> ==See also== * [[Fire and carbon cycling in boreal forests]] * [[Carbon cycle]] ==References== {{reflist|30em}} ==External links== * [http://ipa.arcticportal.org/ International Permafrost Association] * [http://cenperm.ku.dk// Center for Permafrost] * [https://web.archive.org/web/20101124144710/http://science.nasa.gov/missions/carve/ Carbon in Arctic Reservoirs Vulnerability Experiment] {{Global Warming}} {{DEFAULTSORT:Permafrost Carbon Cycle}} [[Category:Climate change feedbacks]] [[Category:Carbon cycle]] [[Category:Permafrost]]'

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'<div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Sub-cycle of the larger global carbon cycle</div> <p class="mw-empty-elt"> </p> <style data-mw-deduplicate="TemplateStyles:r1033289096">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}</style><div role="note" class="hatnote navigation-not-searchable">This article is about movement of carbon in and around permafrost. For other aspects of permafrost, see <a href="/wiki/Permafrost" title="Permafrost">permafrost</a>.</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Schuur_2022_permafrost_carbon_literature.jpeg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Schuur_2022_permafrost_carbon_literature.jpeg/220px-Schuur_2022_permafrost_carbon_literature.jpeg" decoding="async" width="220" height="189" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Schuur_2022_permafrost_carbon_literature.jpeg/330px-Schuur_2022_permafrost_carbon_literature.jpeg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Schuur_2022_permafrost_carbon_literature.jpeg/440px-Schuur_2022_permafrost_carbon_literature.jpeg 2x" data-file-width="1867" data-file-height="1605" /></a><figcaption>The annual number of scientific research papers published on the subject of permafrost carbon has grown from next to nothing around 1990 to around 400 by 2020.<sup id="cite_ref-Schuur2022_1-0" class="reference"><a href="#cite_note-Schuur2022-1">&#91;1&#93;</a></sup></figcaption></figure> <style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist 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class="sidebar-pretitle">Part of a series on the</td></tr><tr><th class="sidebar-title-with-pretitle" style="background:#82C3D8; padding:0.2em; font-size:160%; font-weight:bold;"><a href="/wiki/Carbon_cycle" title="Carbon cycle">Carbon cycle</a></th></tr><tr><td class="sidebar-image"><span typeof="mw:File"><a href="/wiki/File:Carbon_cycle-cute_diagram.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/82/Carbon_cycle-cute_diagram.svg/160px-Carbon_cycle-cute_diagram.svg.png" decoding="async" width="160" height="123" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/82/Carbon_cycle-cute_diagram.svg/240px-Carbon_cycle-cute_diagram.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/82/Carbon_cycle-cute_diagram.svg/320px-Carbon_cycle-cute_diagram.svg.png 2x" data-file-width="600" data-file-height="460" /></a></span></td></tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)">By regions</div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Terrestrial_biological_carbon_cycle" title="Terrestrial biological carbon cycle">Terrestrial</a></li> <li><a href="/wiki/Oceanic_carbon_cycle" title="Oceanic carbon cycle">Marine</a></li> <li><a href="/wiki/Atmospheric_carbon_cycle" title="Atmospheric carbon cycle">Atmospheric</a></li> <li><a href="/wiki/Deep_carbon_cycle" title="Deep carbon cycle">Deep carbon</a></li> <li><a href="/wiki/Soil_carbon" title="Soil carbon">Soil</a></li> <li><a class="mw-selflink selflink">Permafrost</a></li> <li><a href="/wiki/Fire_and_carbon_cycling_in_boreal_forests" title="Fire and carbon cycling in boreal forests">Boreal forest</a></li> <li><a href="/wiki/Geochemistry_of_carbon" title="Geochemistry of carbon">Geochemistry</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Carbon_dioxide" title="Carbon dioxide">Carbon dioxide</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Carbon_dioxide_in_Earth%27s_atmosphere" title="Carbon dioxide in Earth&#39;s atmosphere">In the atmosphere</a></li> <li><a href="/wiki/Ocean_acidification" title="Ocean acidification">Ocean acidification</a></li> <li><a href="/wiki/Carbon_dioxide_removal" title="Carbon dioxide removal">Removal</a></li> <li><a href="/wiki/Space-based_measurements_of_carbon_dioxide" title="Space-based measurements of carbon dioxide">Satellite measurements</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Forms_of_carbon" class="mw-redirect" title="Forms of carbon">Forms of carbon</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="plainlist"> <ul><li><a href="/wiki/Total_carbon" title="Total carbon">Total carbon</a> (TC)</li> <li><a href="/wiki/Total_organic_carbon" title="Total organic carbon">Total organic carbon</a> (TOC)</li> <li><a href="/wiki/Total_inorganic_carbon" title="Total inorganic carbon">Total inorganic carbon</a> (TIC)</li> <li><a href="/wiki/Dissolved_organic_carbon" title="Dissolved organic carbon">Dissolved organic carbon</a> (DOC)</li> <li><a href="/wiki/Dissolved_inorganic_carbon" title="Dissolved inorganic carbon">Dissolved inorganic carbon</a> (DIC)</li> <li><a href="/wiki/Particulate_organic_matter" title="Particulate organic matter">Particulate organic carbon</a> (POC)</li> <li><a href="/wiki/Particulate_inorganic_carbon" title="Particulate inorganic carbon">Particulate inorganic carbon</a> (PIC)</li></ul> </div> <div class="hlist"> <ul><li><a href="/wiki/Primary_production" title="Primary production">Primary production</a> <ul><li><a href="/wiki/Marine_primary_production" title="Marine primary production">marine</a></li></ul></li></ul> </div> <div class="hlist"> <ul><li><a href="/wiki/Black_carbon" title="Black carbon">Black carbon</a></li> <li><a href="/wiki/Blue_carbon" title="Blue carbon">Blue carbon</a></li> <li><a href="/wiki/Kerogen" title="Kerogen">Kerogen</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Metabolic_pathway" title="Metabolic pathway">Metabolic pathways</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Photosynthesis" title="Photosynthesis">Photosynthesis</a></li> <li><a href="/wiki/Chemosynthesis" title="Chemosynthesis">Chemosynthesis</a></li></ul> </div> <div class="hlist"> <ul><li><a href="/wiki/Calvin_cycle" title="Calvin cycle">Calvin cycle</a></li> <li><a href="/wiki/Reverse_Krebs_cycle" title="Reverse Krebs cycle">Reverse Krebs cycle</a></li> <li><a href="/wiki/Carbon_fixation" class="mw-redirect" title="Carbon fixation">Carbon fixation</a> <ul><li><a href="/wiki/C3_carbon_fixation" title="C3 carbon fixation">C3</a></li> <li><a href="/wiki/C4_carbon_fixation" title="C4 carbon fixation">C4</a></li></ul></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Carbon_respiration" title="Carbon respiration">Carbon respiration</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="plainlist"> <ul><li><a href="/wiki/Ecosystem_respiration" title="Ecosystem respiration">Ecosystem respiration</a></li> <li><a href="/wiki/Net_ecosystem_production" title="Net ecosystem production">Net ecosystem production</a></li> <li><a href="/wiki/Photorespiration" title="Photorespiration">Photorespiration</a></li> <li><a href="/wiki/Soil_respiration" title="Soil respiration">Soil respiration</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Carbon_pump" class="mw-redirect" title="Carbon pump">Carbon pumps</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Biological_pump" title="Biological pump">Biological pump</a> <ul><li><a href="/wiki/Martin_curve" title="Martin curve">Martin curve</a></li></ul></li> <li><a href="/wiki/Solubility_pump" title="Solubility pump">Solubility pump</a></li> <li><a href="/wiki/Lipid_pump" title="Lipid pump">Lipid pump</a></li> <li><a href="/wiki/Marine_snow" title="Marine snow">Marine snow</a></li> <li><a href="/wiki/Microbial_loop" title="Microbial loop">Microbial loop</a></li> <li><a href="/wiki/Viral_shunt" title="Viral shunt">Viral shunt</a></li> <li><a href="/wiki/Jelly-falls" title="Jelly-falls">Jelly pump</a></li> <li><a href="/wiki/Whale_feces" title="Whale feces">Whale pump</a></li> <li><a href="/wiki/Continental_shelf_pump" title="Continental shelf pump">Continental shelf pump</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Carbon_sequestration" title="Carbon sequestration">Carbon sequestration</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Carbon_sink" title="Carbon sink">Carbon sink</a></li> <li><a href="/wiki/Mycorrhizal_fungi_and_soil_carbon_storage" title="Mycorrhizal fungi and soil carbon storage">Soil carbon storage</a></li> <li><a href="/wiki/Marine_sediment" title="Marine sediment">Marine sediment</a> <ul><li><a href="/wiki/Pelagic_sediment" title="Pelagic sediment">pelagic sediment</a></li></ul></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Methane" title="Methane">Methane</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Atmospheric_methane" title="Atmospheric methane">Atmospheric methane</a></li> <li><a href="/wiki/Methanogenesis" title="Methanogenesis">Methanogenesis</a></li> <li><a href="/wiki/Methane_emissions" title="Methane emissions">Methane emissions</a> <ul><li><a href="/wiki/Arctic_methane_emissions" title="Arctic methane emissions">Arctic</a></li> <li><a href="/wiki/Greenhouse_gas_emissions_from_wetlands" title="Greenhouse gas emissions from wetlands">Wetland</a></li></ul></li> <li><a href="/wiki/Aerobic_methane_production" title="Aerobic methane production">Aerobic production</a></li> <li><a href="/wiki/Clathrate_gun_hypothesis" title="Clathrate gun hypothesis">Clathrate gun hypothesis</a></li> <li><a href="/wiki/Carbon_dioxide_clathrate" title="Carbon dioxide clathrate">Carbon dioxide clathrate</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)"><a href="/wiki/Biogeochemical_cycle" title="Biogeochemical cycle">Biogeochemical</a></div><div class="sidebar-list-content mw-collapsible-content"><div class="hlist"> <ul><li><a href="/wiki/Marine_biogeochemical_cycles" title="Marine biogeochemical cycles">Marine cycles</a></li> <li><a href="/wiki/Nutrient_cycle" title="Nutrient cycle">Nutrient cycle</a></li> <li><a href="/wiki/Carbonate%E2%80%93silicate_cycle" title="Carbonate–silicate cycle">Carbonate–silicate cycle</a></li> <li><a href="/wiki/Carbonate_compensation_depth" title="Carbonate compensation depth">Carbonate compensation depth</a></li> <li><a href="/wiki/Great_Calcite_Belt" title="Great Calcite Belt">Great Calcite Belt</a></li> <li><a href="/wiki/Redfield_ratio" title="Redfield ratio">Redfield ratio</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-content"> <div class="sidebar-list mw-collapsible mw-collapsed"><div class="sidebar-list-title" style="text-align:center;font-size:100%;font-weight:bold;;color: var(--color-base)">Other</div><div 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href="/wiki/Total_Carbon_Column_Observing_Network" title="Total Carbon Column Observing Network">Total Carbon Column Observing Network</a></li> <li><a href="/wiki/C4MIP" title="C4MIP">C4MIP</a></li> <li><a href="/wiki/CO2SYS" title="CO2SYS">CO2SYS</a></li></ul> </div></div></div></td> </tr><tr><td class="sidebar-below hlist" style="background-color: #82C3D8; border-color: #A2B8BF"> <ul><li><span class="nowrap"><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span>&#160;<a href="/wiki/Category:Carbon_cycle" title="Category:Carbon cycle">Category</a></span></li></ul></td></tr><tr><td class="sidebar-navbar"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1063604349">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Carbon_cycle" title="Template:Carbon cycle"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/w/index.php?title=Template_talk:Carbon_cycle&amp;action=edit&amp;redlink=1" class="new" title="Template talk:Carbon cycle (page does not exist)"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Carbon_cycle" title="Special:EditPage/Template:Carbon cycle"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table> <p>The <b>permafrost carbon cycle</b> or <b>Arctic carbon cycle</b> is a sub-cycle of the larger global <a href="/wiki/Carbon_cycle" title="Carbon cycle">carbon cycle</a>. <a href="/wiki/Permafrost" title="Permafrost">Permafrost</a> is defined as subsurface material that remains below 0^o C (32^o F) for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir, one which was often neglected in the initial research determining global terrestrial carbon reservoirs. Since the start of the 2000s, however, far more attention has been paid to the subject,<sup id="cite_ref-zimov_2-0" class="reference"><a href="#cite_note-zimov-2">&#91;2&#93;</a></sup> with an enormous growth both in general attention and in the scientific research output.<sup id="cite_ref-Schuur2022_1-1" class="reference"><a href="#cite_note-Schuur2022-1">&#91;1&#93;</a></sup> </p><p>The permafrost carbon cycle deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to <a href="/wiki/Atmosphere_of_Earth" title="Atmosphere of Earth">the atmosphere</a>, back to vegetation, and, finally, back to permafrost soils through burial and sedimentation due to cryogenic processes. Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle. The cycle includes the exchange of <a href="/wiki/Carbon_dioxide" title="Carbon dioxide">carbon dioxide</a> and <a href="/wiki/Methane" title="Methane">methane</a> between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water as methane, <a href="/wiki/Dissolved_organic_carbon" title="Dissolved organic carbon">dissolved organic carbon</a>, <a href="/wiki/Dissolved_inorganic_carbon" title="Dissolved inorganic carbon">dissolved inorganic carbon</a>, <a href="/wiki/Particulate_inorganic_carbon" title="Particulate inorganic carbon">particulate inorganic carbon</a>, and <a href="/wiki/Particulate_organic_carbon" class="mw-redirect" title="Particulate organic carbon">particulate organic carbon</a>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3">&#91;3&#93;</a></sup> </p> <div id="toc" class="toc" role="navigation" aria-labelledby="mw-toc-heading"><input type="checkbox" role="button" id="toctogglecheckbox" class="toctogglecheckbox" style="display:none" /><div class="toctitle" lang="en" dir="ltr"><h2 id="mw-toc-heading">Contents</h2><span class="toctogglespan"><label class="toctogglelabel" for="toctogglecheckbox"></label></span></div> <ul> <li class="toclevel-1 tocsection-1"><a href="#Storage"><span class="tocnumber">1</span> <span class="toctext">Storage</span></a> <ul> <li class="toclevel-2 tocsection-2"><a href="#Processes"><span class="tocnumber">1.1</span> <span class="toctext">Processes</span></a></li> <li class="toclevel-2 tocsection-3"><a href="#Current_estimates"><span class="tocnumber">1.2</span> <span class="toctext">Current estimates</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-4"><a href="#Carbon_release_from_the_permafrost"><span class="tocnumber">2</span> <span class="toctext">Carbon release from the permafrost</span></a> <ul> <li class="toclevel-2 tocsection-5"><a href="#Carbon_dioxide_emissions"><span class="tocnumber">2.1</span> <span class="toctext">Carbon dioxide emissions</span></a></li> <li class="toclevel-2 tocsection-6"><a href="#Methane_emissions"><span class="tocnumber">2.2</span> <span class="toctext">Methane emissions</span></a></li> <li class="toclevel-2 tocsection-7"><a href="#Subsea_permafrost"><span class="tocnumber">2.3</span> <span class="toctext">Subsea permafrost</span></a></li> <li class="toclevel-2 tocsection-8"><a href="#Cumulative"><span class="tocnumber">2.4</span> <span class="toctext">Cumulative</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-9"><a href="#See_also"><span class="tocnumber">3</span> <span class="toctext">See also</span></a></li> <li class="toclevel-1 tocsection-10"><a href="#References"><span class="tocnumber">4</span> <span class="toctext">References</span></a></li> <li class="toclevel-1 tocsection-11"><a href="#External_links"><span class="tocnumber">5</span> <span class="toctext">External links</span></a></li> </ul> </div> <div class="mw-heading mw-heading2"><h2 id="Storage">Storage</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=1" title="Edit section: Storage" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=1" title="Edit section&#039;s source code: Storage"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Soils, in general, are the largest reservoirs of carbon in <a href="/wiki/Ecosystem" title="Ecosystem">terrestrial ecosystems</a>. This is also true for soils in the Arctic that are underlain by permafrost. In 2003, Tarnocai, et al. used the Northern and Mid Latitudes Soil Database to make a determination of carbon stocks in <a href="/wiki/Gelisols" class="mw-redirect" title="Gelisols">cryosols</a>—soils containing permafrost within two meters of the soil surface.<sup id="cite_ref-kimble_4-0" class="reference"><a href="#cite_note-kimble-4">&#91;4&#93;</a></sup> Permafrost affected soils cover nearly 9% of the Earth's land area, yet store between 25 and 50% of the soil organic carbon. These estimates show that permafrost soils are an important carbon pool.<sup id="cite_ref-bockheim_5-0" class="reference"><a href="#cite_note-bockheim-5">&#91;5&#93;</a></sup> These soils not only contain large amounts of carbon, but also sequester carbon through <a href="/wiki/Cryoturbation" title="Cryoturbation">cryoturbation</a> and cryogenic processes.<sup id="cite_ref-kimble_4-1" class="reference"><a href="#cite_note-kimble-4">&#91;4&#93;</a></sup><sup id="cite_ref-tarnocai_6-0" class="reference"><a href="#cite_note-tarnocai-6">&#91;6&#93;</a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Processes">Processes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=2" title="Edit section: Processes" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=2" title="Edit section&#039;s source code: Processes"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Carbon is not produced by permafrost. Organic carbon derived from terrestrial vegetation must be incorporated into the soil column and subsequently be incorporated into permafrost to be effectively stored. Because permafrost responds to climate changes slowly, carbon storage removes carbon from the atmosphere for long periods of time. <a href="/wiki/Radiocarbon" class="mw-redirect" title="Radiocarbon">Radiocarbon</a> dating techniques reveal that carbon within permafrost is often thousands of years old.<sup id="cite_ref-guo_7-0" class="reference"><a href="#cite_note-guo-7">&#91;7&#93;</a></sup><sup id="cite_ref-nowinski_8-0" class="reference"><a href="#cite_note-nowinski-8">&#91;8&#93;</a></sup> Carbon storage in permafrost is the result of two primary processes. </p> <ul><li>The first process that captures carbon and stores it is <a href="/wiki/Syngenetic_permafrost_growth" title="Syngenetic permafrost growth">syngenetic permafrost growth</a>.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9">&#91;9&#93;</a></sup> This process is the result of a constant active layer where thickness and energy exchange between permafrost, active layer, biosphere, and atmosphere, resulting in the vertical increase of the soil surface elevation. This aggradation of soil is the result of <a href="/wiki/Aeolian_processes" title="Aeolian processes">aeolian</a> or <a href="/wiki/Fluvial" class="mw-redirect" title="Fluvial">fluvial</a> sedimentation and/or <a href="/wiki/Peat" title="Peat">peat</a> formation. Peat accumulation rates are as high as 0.5mm/yr while sedimentation may cause a rise of 0.7mm/yr. Thick silt deposits resulting from abundant loess deposition during the <a href="/wiki/Last_glacial_maximum" class="mw-redirect" title="Last glacial maximum">last glacial maximum</a> form thick carbon-rich soils known as <a href="/wiki/Yedoma" title="Yedoma">yedoma</a>.<sup id="cite_ref-schuur_10-0" class="reference"><a href="#cite_note-schuur-10">&#91;10&#93;</a></sup> As this process occurs, the organic and mineral soil that is deposited is incorporated into the permafrost as the permafrost surface rises.</li> <li>The second process responsible for storing carbon is <a href="/wiki/Cryoturbation" title="Cryoturbation">cryoturbation</a>, the mixing of soil due to freeze-thaw cycles. Cryoturbation moves carbon from the surface to depths within the soil profile. <a href="/wiki/Frost_heaving" title="Frost heaving">Frost heaving</a> is the most common form of cryoturbation. Eventually, carbon that originates at the surface moves deep enough into the active layer to be incorporated into permafrost. When cryoturbation and the deposition of sediments act together carbon storage rates increase.<sup id="cite_ref-schuur_10-1" class="reference"><a href="#cite_note-schuur-10">&#91;10&#93;</a></sup></li></ul> <div class="mw-heading mw-heading3"><h3 id="Current_estimates">Current estimates</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=3" title="Edit section: Current estimates" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=3" title="Edit section&#039;s source code: Current estimates"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Hugelius_2020_peatland_projections.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Hugelius_2020_peatland_projections.jpg/220px-Hugelius_2020_peatland_projections.jpg" decoding="async" width="220" height="252" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Hugelius_2020_peatland_projections.jpg/330px-Hugelius_2020_peatland_projections.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Hugelius_2020_peatland_projections.jpg/440px-Hugelius_2020_peatland_projections.jpg 2x" data-file-width="762" data-file-height="872" /></a><figcaption>Permafrost peatlands under varying extent of global warming, and the resultant emissions as a fraction of anthropogenic emissions needed to cause that extent of warming.<sup id="cite_ref-Hugelius2020_11-0" class="reference"><a href="#cite_note-Hugelius2020-11">&#91;11&#93;</a></sup></figcaption></figure> <p>It is estimated that the total soil organic carbon (SOC) stock in northern circumpolar permafrost region equals around 1,460–1,600 <a href="/wiki/Kilogram#SI_multiples" title="Kilogram">Pg</a>.<sup id="cite_ref-tarnocai_6-1" class="reference"><a href="#cite_note-tarnocai-6">&#91;6&#93;</a></sup> (1 Pg = 1 Gt = 10¹⁵g)<sup id="cite_ref-12" class="reference"><a href="#cite_note-12">&#91;12&#93;</a></sup><sup id="cite_ref-ARC2019_13-0" class="reference"><a href="#cite_note-ARC2019-13">&#91;13&#93;</a></sup> With the <a href="/wiki/Tibetan_Plateau" title="Tibetan Plateau">Tibetan Plateau</a> carbon content included, the total carbon pools in the permafrost of the Northern Hemisphere is likely to be around 1832 Gt.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14">&#91;14&#93;</a></sup> This estimation of the amount of carbon stored in permafrost soils is more than double the amount currently in the atmosphere.<sup id="cite_ref-zimov_2-1" class="reference"><a href="#cite_note-zimov-2">&#91;2&#93;</a></sup> </p><p>Soil column in the permafrost soils is generally broken into three horizons, 0–30&#160;cm, 0–100&#160;cm, and 1–300&#160;cm. The uppermost horizon (0–30&#160;cm) contains approximately 200 Pg of organic carbon. The 0–100&#160;cm horizon contains an estimated 500 Pg of organic carbon, and the 0–300&#160;cm horizon contains an estimated 1024 Pg of organic carbon. These estimates more than doubled the previously known carbon pools in permafrost soils.<sup id="cite_ref-kimble_4-2" class="reference"><a href="#cite_note-kimble-4">&#91;4&#93;</a></sup><sup id="cite_ref-bockheim_5-1" class="reference"><a href="#cite_note-bockheim-5">&#91;5&#93;</a></sup><sup id="cite_ref-tarnocai_6-2" class="reference"><a href="#cite_note-tarnocai-6">&#91;6&#93;</a></sup> Additional carbon stocks exist in <a href="/wiki/Yedoma" title="Yedoma">yedoma</a> (400 Pg), carbon rich <a href="/wiki/Loess" title="Loess">loess</a> deposits found throughout Siberia and isolated regions of North America, and deltaic deposits (240 Pg) throughout the Arctic. These deposits are generally deeper than the 3 m investigated in traditional studies.<sup id="cite_ref-tarnocai_6-3" class="reference"><a href="#cite_note-tarnocai-6">&#91;6&#93;</a></sup> Many concerns arise because of the large amount of carbon stored in permafrost soils. Until recently, the amount of carbon present in permafrost was not taken into account in climate models and global carbon budgets.<sup id="cite_ref-zimov_2-2" class="reference"><a href="#cite_note-zimov-2">&#91;2&#93;</a></sup><sup id="cite_ref-schuur_10-2" class="reference"><a href="#cite_note-schuur-10">&#91;10&#93;</a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Carbon_release_from_the_permafrost">Carbon release from the permafrost</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=4" title="Edit section: Carbon release from the permafrost" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=4" title="Edit section&#039;s source code: Carbon release from the permafrost"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Carbon is continually cycling between soils, vegetation, and the atmosphere. As climate change increases mean annual air temperatures throughout the Arctic, it extends permafrost thaw and deepens the active layer, exposing old carbon that has been in storage for decades to millennia to biogenic processes which facilitate its entrance into the atmosphere. In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per 1&#160;°C (1.8&#160;°F)of global warming.<sup id="cite_ref-AR6_WG1_Chapter922_15-0" class="reference"><a href="#cite_note-AR6_WG1_Chapter922-15">&#91;15&#93;</a></sup><sup class="reference nowrap"><span title="Page / location: 1283">&#58;&#8202;1283&#8202;</span></sup> According to the <a href="/wiki/IPCC_Sixth_Assessment_Report" title="IPCC Sixth Assessment Report">IPCC Sixth Assessment Report</a>, there is high confidence that global warming over the last few decades has led to widespread increases in permafrost temperature.<sup id="cite_ref-AR6_WG1_Chapter922_15-1" class="reference"><a href="#cite_note-AR6_WG1_Chapter922-15">&#91;15&#93;</a></sup><sup class="reference nowrap"><span title="Page / location: 1237">&#58;&#8202;1237&#8202;</span></sup> Observed warming was up to 3&#160;°C (5.4&#160;°F) in parts of Northern Alaska (early 1980s to mid-2000s) and up to 2&#160;°C (3.6&#160;°F) in parts of the Russian European North (1970–2020), and active layer thickness has increased in the European and Russian Arctic across the 21st century and at high elevation areas in Europe and Asia since the 1990s.<sup id="cite_ref-AR6_WG1_Chapter922_15-2" class="reference"><a href="#cite_note-AR6_WG1_Chapter922-15">&#91;15&#93;</a></sup><sup class="reference nowrap"><span title="Page / location: 1237">&#58;&#8202;1237&#8202;</span></sup> In <a href="/wiki/Yukon" title="Yukon">Yukon</a>, the zone of continuous permafrost might have moved 100 kilometres (62&#160;mi) poleward since 1899, but accurate records only go back 30 years. Based on high agreement across model projections, fundamental process understanding, and paleoclimate evidence, it is virtually certain that permafrost extent and volume will continue to shrink as global climate warms.<sup id="cite_ref-AR6_WG1_Chapter922_15-3" class="reference"><a href="#cite_note-AR6_WG1_Chapter922-15">&#91;15&#93;</a></sup><sup class="reference nowrap"><span title="Page / location: 1283">&#58;&#8202;1283&#8202;</span></sup> </p> <figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Douglas_2020_precipitation_layers.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Douglas_2020_precipitation_layers.png/220px-Douglas_2020_precipitation_layers.png" decoding="async" width="220" height="373" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Douglas_2020_precipitation_layers.png/330px-Douglas_2020_precipitation_layers.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Douglas_2020_precipitation_layers.png/440px-Douglas_2020_precipitation_layers.png 2x" data-file-width="928" data-file-height="1574" /></a><figcaption>Greater summer precipitation increases the depth of permafrost layer subject to thaw, in different Arctic permafrost environments.<sup id="cite_ref-Douglas2020_16-0" class="reference"><a href="#cite_note-Douglas2020-16">&#91;16&#93;</a></sup></figcaption></figure> <p>Carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it a <a href="/wiki/Climate_change_feedback#Positive_feedbacks" class="mw-redirect" title="Climate change feedback">positive climate change feedback</a>. The warming also intensifies Arctic <a href="/wiki/Water_cycle" title="Water cycle">water cycle</a>, and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.<sup id="cite_ref-Douglas2020_16-1" class="reference"><a href="#cite_note-Douglas2020-16">&#91;16&#93;</a></sup> The amount of carbon that will be released from warming conditions depends on depth of thaw, carbon content within the thawed soil, physical changes to the environment<sup id="cite_ref-nowinski_8-1" class="reference"><a href="#cite_note-nowinski-8">&#91;8&#93;</a></sup> and microbial and vegetation activity in the soil. Microbial respiration is the primary process through which old permafrost carbon is re-activated and enters the atmosphere. The rate of microbial decomposition within organic soils, including thawed permafrost, depends on environmental controls, such as soil temperature, moisture availability, nutrient availability, and oxygen availability.<sup id="cite_ref-schuur_10-3" class="reference"><a href="#cite_note-schuur-10">&#91;10&#93;</a></sup> In particular, sufficient concentrations of iron oxides in some permafrost soils can inhibit microbial respiration and prevent carbon mobilization: however, this protection only lasts until carbon is separated from the iron oxides by Fe-reducing bacteria, which is only a matter of time under the typical conditions.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17">&#91;17&#93;</a></sup> Depending on the soil type, <a href="/wiki/Iron(III)_oxide" title="Iron(III) oxide">Iron(III) oxide</a> can boost oxidation of methane to carbon dioxide in the soil, but it can also amplify methane production by acetotrophs: these soil processes are not yet fully understood.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18">&#91;18&#93;</a></sup> </p><p>Altogether, the likelihood of the entire carbon pool mobilizing and entering the atmosphere is low despite the large volumes stored in the soil. Although temperatures will increase, this does not imply complete loss of permafrost and mobilization of the entire carbon pool. Much of the ground underlain by permafrost will remain frozen even if warming temperatures increase the thaw depth or increase thermokarsting and permafrost degradation.<sup id="cite_ref-bockheim_5-2" class="reference"><a href="#cite_note-bockheim-5">&#91;5&#93;</a></sup> Moreover, other elements such as <a href="/wiki/Iron" title="Iron">iron</a> and <a href="/wiki/Aluminum" class="mw-redirect" title="Aluminum">aluminum</a> can <a href="/wiki/Adsorbtion" class="mw-redirect" title="Adsorbtion">adsorb</a> some of the mobilized <a href="/wiki/Soil_carbon" title="Soil carbon">soil carbon</a> before it reaches the atmosphere, and they are particularly prominent in the mineral sand layers which often overlay permafrost.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19">&#91;19&#93;</a></sup> On the other hand, once the permafrost area thaws, it will not go back to being permafrost for centuries even if the temperature increase reversed, making it one of the best-known examples of <a href="/wiki/Tipping_points_in_the_climate_system" title="Tipping points in the climate system">tipping points in the climate system</a>. </p><p>A 1993 study suggested that while the tundra was a <a href="/wiki/Carbon_sink" title="Carbon sink">carbon sink</a> until the end of the 1970s, it had already transitioned to a net carbon source by the time the study concluded.<sup id="cite_ref-Oechel1993_20-0" class="reference"><a href="#cite_note-Oechel1993-20">&#91;20&#93;</a></sup> The 2019 Arctic Report Card estimated that Arctic permafrost releases between 0.3 and 0.6 Pg C per year.<sup id="cite_ref-ARC2019_13-1" class="reference"><a href="#cite_note-ARC2019-13">&#91;13&#93;</a></sup> That same year, a study settled on the 0.6 Pg C figure, as the net difference between the annual emissions of 1,66 Pg C during the winter season (October–April), and the model-estimated vegetation carbon uptake of 1 Pg C during the growing season. It estimated that under <a href="/wiki/Representative_Concentration_Pathway" title="Representative Concentration Pathway">RCP</a> 8.5, a scenario of continually accelerating greenhouse gas emissions, winter CO<sub style="font-size: 80%;vertical-align: -0.35em">2</sub> emissions from the northern permafrost domain would increase 41% by 2100. Under the "intermediate" scenario RCP 4.5, where greenhouse gas emissions peak and plateau within the next two decades, before gradually declining for the rest of the century (a rate of mitigation deeply insufficient to meet the <a href="/wiki/Paris_Agreement" title="Paris Agreement">Paris Agreement</a> goals) permafrost carbon emissions would increase by 17%.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21">&#91;21&#93;</a></sup> In 2022, this was challenged by a study which used a record of atmospheric observations between 1980 and 2017, and found that permafrost regions have been gaining carbon on net, as process-based models underestimated net CO₂ uptake in the permafrost regions and overestimated it in the forested regions, where increased respiration in response to warming offsets more of the gains than was previously understood.<sup id="cite_ref-Liu2022_22-0" class="reference"><a href="#cite_note-Liu2022-22">&#91;22&#93;</a></sup> </p><p>Notably, estimates of carbon release alone do not fully represent the impact of permafrost thaw on climate change. This is because carbon can either be released as carbon dioxide (CO₂) or methane (CH₄). <a href="/wiki/Aerobic_respiration" class="mw-redirect" title="Aerobic respiration">Aerobic respiration</a> releases carbon dioxide, while <a href="/wiki/Anaerobic_respiration" title="Anaerobic respiration">anaerobic respiration</a> releases methane. This is a substantial difference, as while biogenic methane lasts less than 12 years in the atmosphere, its <a href="/wiki/Global_warming_potential" title="Global warming potential">global warming potential</a> is around 80 times larger than that of CO₂ over a 20-year period and between 28 and 40 times larger over a 100-year period.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23">&#91;23&#93;</a></sup><sup id="cite_ref-24" class="reference"><a href="#cite_note-24">&#91;24&#93;</a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Carbon_dioxide_emissions">Carbon dioxide emissions</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=5" title="Edit section: Carbon dioxide emissions" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=5" title="Edit section&#039;s source code: Carbon dioxide emissions"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Liu_2022_permafrost_tree_cover.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/91/Liu_2022_permafrost_tree_cover.png/220px-Liu_2022_permafrost_tree_cover.png" decoding="async" width="220" height="164" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/91/Liu_2022_permafrost_tree_cover.png/330px-Liu_2022_permafrost_tree_cover.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/91/Liu_2022_permafrost_tree_cover.png/440px-Liu_2022_permafrost_tree_cover.png 2x" data-file-width="1997" data-file-height="1485" /></a><figcaption>Recent observations suggest that CO<sub style="font-size: 80%;vertical-align: -0.35em">2</sub> absorption had been increasing at a faster rate over the areas with a lot of permafrost and limited tree cover than over the areas with extensive tree cover.<sup id="cite_ref-Liu2022_22-1" class="reference"><a href="#cite_note-Liu2022-22">&#91;22&#93;</a></sup></figcaption></figure> <p>Most of the permafrost soil are oxic and provide a suitable environment for aerobic microbial respiration. As such, carbon dioxide emissions account for the overwhelming majority of permafrost emissions and of the Arctic emissions in general.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25">&#91;25&#93;</a></sup> There's some debate over whether the observed emissions from permafrost soils primarily constitute microbial respiration of ancient carbon, or simply greater respiration of modern-day carbon (i.e. leaf litter), due to warmer soils intensifying microbial metabolism. Studies published in the early 2020s indicate that while soil microbiota still primarily consumes and respires modern carbon when plants grow during the spring and summer, these microorganisms then sustain themselves on ancient carbon during the winter, releasing it into the atmosphere.<sup id="cite_ref-26" class="reference"><a href="#cite_note-26">&#91;26&#93;</a></sup><sup id="cite_ref-27" class="reference"><a href="#cite_note-27">&#91;27&#93;</a></sup> </p><p>On the other hand, former permafrost areas consistently see increased vegetation growth, or primary production, as plants can set down deeper roots in the thawed soil and grow larger and uptake more carbon. This is generally the main counteracting feedback on permafrost carbon emissions. However, in areas with streams and other waterways, more of their leaf litter enters those waterways, increasing their dissolved organic carbon content. Leaching of soil organic carbon from permafrost soils is also accelerated by warming climate and by erosion along river and stream banks freeing the carbon from the previously frozen soil.<sup id="cite_ref-guo_7-1" class="reference"><a href="#cite_note-guo-7">&#91;7&#93;</a></sup> Moreover, thawed areas become more vulnerable to wildfires, which alter landscape and release large quantities of stored organic carbon through combustion. As these fires burn, they remove organic matter from the surface. Removal of the protective organic mat that insulates the soil exposes the underlying soil and permafrost to increased <a href="/wiki/Solar_radiation" class="mw-redirect" title="Solar radiation">solar radiation</a>, which in turn increases the soil temperature, active layer thickness, and changes soil moisture. Changes in the soil moisture and saturation alter the ratio of <a href="/wiki/Oxic" class="mw-redirect" title="Oxic">oxic</a> to anoxic decomposition within the soil.<sup id="cite_ref-meyers_28-0" class="reference"><a href="#cite_note-meyers-28">&#91;28&#93;</a></sup> </p><p>A hypothesis promoted by <a href="/wiki/Sergey_Zimov" title="Sergey Zimov">Sergey Zimov</a> is that the reduction of herds of large herbivores has increased the ratio of energy emission and energy absorption tundra (energy balance) in a manner that increases the tendency for net thawing of permafrost.<sup id="cite_ref-29" class="reference"><a href="#cite_note-29">&#91;29&#93;</a></sup> He is testing this hypothesis in an experiment at <a href="/wiki/Pleistocene_Park" title="Pleistocene Park">Pleistocene Park</a>, a nature reserve in northeastern Siberia.<sup id="cite_ref-30" class="reference"><a href="#cite_note-30">&#91;30&#93;</a></sup> On the other hand, warming allows the <a href="/wiki/Beaver" title="Beaver">beavers</a> to extend their habitat further north, where their <a href="/wiki/Beaver_dam#Effects" title="Beaver dam">dams impair</a> boat travel, impact access to food, affect water quality, and endanger downstream fish populations.<sup id="cite_ref-Guardian_20220104_31-0" class="reference"><a href="#cite_note-Guardian_20220104-31">&#91;31&#93;</a></sup> Pools formed by the dams store heat, thus changing local <a href="/wiki/Hydrology" title="Hydrology">hydrology</a> and causing localized permafrost thaw.<sup id="cite_ref-Guardian_20220104_31-1" class="reference"><a href="#cite_note-Guardian_20220104-31">&#91;31&#93;</a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Methane_emissions">Methane emissions</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=6" title="Edit section: Methane emissions" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=6" title="Edit section&#039;s source code: Methane emissions"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1033289096"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Arctic_methane_emissions" title="Arctic methane emissions">Arctic methane emissions</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Bernhard_2022_RTS_activity.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/92/Bernhard_2022_RTS_activity.png/220px-Bernhard_2022_RTS_activity.png" decoding="async" width="220" height="162" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/92/Bernhard_2022_RTS_activity.png/330px-Bernhard_2022_RTS_activity.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/92/Bernhard_2022_RTS_activity.png/440px-Bernhard_2022_RTS_activity.png 2x" data-file-width="624" data-file-height="459" /></a><figcaption>Carbon cycle accelerates in the wake of abrupt thaw (orange) relative to the previous state of the area (blue, black).<sup id="cite_ref-Bernhard2022_32-0" class="reference"><a href="#cite_note-Bernhard2022-32">&#91;32&#93;</a></sup></figcaption></figure> <p>Global warming in the Arctic accelerates methane release from both existing stores and <a href="/wiki/Methanogenesis" title="Methanogenesis">methanogenesis</a> in rotting <a href="/wiki/Biomass_(ecology)" title="Biomass (ecology)">biomass</a>.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33">&#91;33&#93;</a></sup> Methanogenesis requires thoroughly anaerobic environments, which slows down the mobilization of old carbon. A 2015 <i><a href="/wiki/Nature_(magazine)" class="mw-redirect" title="Nature (magazine)">Nature</a></i> review estimated that the cumulative emissions from thawed anaerobic permafrost sites were 75–85% lower than the cumulative emissions from aerobic sites, and that even there, methane emissions amounted to only 3% to 7% of CO₂ emitted in situ. While they represented between 25% and 45% of the CO₂'s potential impact on climate over a 100-year timescale, the review concluded that aerobic permafrost thaw still had a greater warming impact overall.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34">&#91;34&#93;</a></sup> In 2018, however, another study in <i><a href="/wiki/Nature_Climate_Change" title="Nature Climate Change">Nature Climate Change</a></i> performed seven-year incubation experiments and found that methane production became equivalent to CO₂ production once a methanogenic microbial community became established at the anaerobic site. This finding had substantially raised the overall warming impact represented by anaerobic thaw sites.<sup id="cite_ref-35" class="reference"><a href="#cite_note-35">&#91;35&#93;</a></sup> </p><p>Since methanogenesis requires anaerobic environments, it is frequently associated with Arctic lakes, where the emergence of bubbles of methane can be observed.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36">&#91;36&#93;</a></sup><sup id="cite_ref-NYT_Thaw_37-0" class="reference"><a href="#cite_note-NYT_Thaw-37">&#91;37&#93;</a></sup> Lakes produced by the thaw of particularly ice-rich permafrost are known as <a href="/wiki/Thermokarst" title="Thermokarst">thermokarst</a> lakes. Not all of the methane produced in the sediment of a lake reaches the atmosphere, as it can get oxidized in the water column or even within the sediment itself:<sup id="cite_ref-38" class="reference"><a href="#cite_note-38">&#91;38&#93;</a></sup> However, 2022 observations indicate that at least half of the methane produced within thermokarst lakes reaches the atmosphere.<sup id="cite_ref-39" class="reference"><a href="#cite_note-39">&#91;39&#93;</a></sup> Another process which frequently results in substantial methane emissions is the <a href="/wiki/Erosion" title="Erosion">erosion</a> of permafrost-stabilized hillsides and their ultimate collapse.<sup id="cite_ref-40" class="reference"><a href="#cite_note-40">&#91;40&#93;</a></sup> Altogether, these two processes - hillside collapse (also known as retrogressive thaw slump, or RTS) and thermokarst lake formation - are collectively described as abrupt thaw, as they can rapidly expose substantial volumes of soil to microbial respiration in a matter of days, as opposed to the gradual, cm by cm, thaw of formerly frozen soil which dominates across most permafrost environments. This rapidity was illustrated in 2019, when three permafrost sites which would have been safe from thawing under the "intermediate" <a href="/wiki/Representative_Concentration_Pathway" title="Representative Concentration Pathway">Representative Concentration Pathway</a> 4.5 for 70 more years had undergone abrupt thaw.<sup id="cite_ref-TGRomanovsky_41-0" class="reference"><a href="#cite_note-TGRomanovsky-41">&#91;41&#93;</a></sup> Another example occurred in the wake of a 2020 Siberian heatwave, which was found to have increased RTS numbers 17-fold across the northern <a href="/wiki/Taymyr_Peninsula" title="Taymyr Peninsula">Taymyr Peninsula</a> – from 82 to 1404, while the resultant soil carbon mobilization increased 28-fold, to an average of 11 grams of carbon per square meter per year across the peninsula (with a range between 5 and 38 grams).<sup id="cite_ref-Bernhard2022_32-1" class="reference"><a href="#cite_note-Bernhard2022-32">&#91;32&#93;</a></sup> </p><p>Until recently, Permafrost carbon feedback (PCF) modeling had mainly focused on gradual permafrost thaw, due to the difficulty of modelling abrupt thaw, and because of the flawed assumptions about the rates of methane production.<sup id="cite_ref-:5_42-0" class="reference"><a href="#cite_note-:5-42">&#91;42&#93;</a></sup> Nevertheless, a study from 2018, by using field observations, radiocarbon dating, and remote sensing to account for <a href="/wiki/Thermokarst" title="Thermokarst">thermokarst</a> lakes, determined that abrupt thaw will more than double permafrost carbon emissions by 2100.<sup id="cite_ref-:6_43-0" class="reference"><a href="#cite_note-:6-43">&#91;43&#93;</a></sup> And a second study from 2020, showed that under the scenario of continually accelerating emissions (RCP 8.5), abrupt thaw carbon emissions across 2.5 million km² are projected to provide the same feedback as gradual thaw of near-surface permafrost across the whole 18 million km² it occupies.<sup id="cite_ref-:5_42-1" class="reference"><a href="#cite_note-:5-42">&#91;42&#93;</a></sup> Thus, abrupt thaw adds between 60 and 100 gigatonnes of carbon by 2300,<sup id="cite_ref-44" class="reference"><a href="#cite_note-44">&#91;44&#93;</a></sup> increasing carbon emissions by ~125–190% when compared to gradual thaw alone.<sup id="cite_ref-:5_42-2" class="reference"><a href="#cite_note-:5-42">&#91;42&#93;</a></sup><sup id="cite_ref-:6_43-1" class="reference"><a href="#cite_note-:6-43">&#91;43&#93;</a></sup> </p> <figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Hefferman_2022_bog_methane.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Hefferman_2022_bog_methane.png/220px-Hefferman_2022_bog_methane.png" decoding="async" width="220" height="95" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Hefferman_2022_bog_methane.png/330px-Hefferman_2022_bog_methane.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Hefferman_2022_bog_methane.png/440px-Hefferman_2022_bog_methane.png 2x" data-file-width="2067" data-file-height="889" /></a><figcaption>Methane emissions from thawed permafrost appear to decrease as bog matures over time.<sup id="cite_ref-Heffernan2022_45-0" class="reference"><a href="#cite_note-Heffernan2022-45">&#91;45&#93;</a></sup></figcaption></figure> <p>However, there is still scientific debate about the rate and the trajectory of methane production in the thawed permafrost environments. For instance, a 2017 paper suggested that even in the thawing peatlands with frequent thermokarst lakes, less than 10% of methane emissions can be attributed to the old, thawed carbon, and the rest is anaerobic decomposition of modern carbon.<sup id="cite_ref-46" class="reference"><a href="#cite_note-46">&#91;46&#93;</a></sup> A follow-up study in 2018 had even suggested that increased uptake of carbon due to rapid peat formation in the thermokarst wetlands would compensate for the increased methane release.<sup id="cite_ref-47" class="reference"><a href="#cite_note-47">&#91;47&#93;</a></sup> Another 2018 paper suggested that permafrost emissions are limited following thermokarst thaw, but are substantially greater in the aftermath of wildfires.<sup id="cite_ref-48" class="reference"><a href="#cite_note-48">&#91;48&#93;</a></sup> In 2022, a paper demonstrated that peatland methane emissions from permafrost thaw are initially quite high (82 milligrams of methane per square meter per day), but decline by nearly three times as the permafrost bog matures, suggesting a reduction in methane emissions in several decades to a century following abrupt thaw.<sup id="cite_ref-Heffernan2022_45-1" class="reference"><a href="#cite_note-Heffernan2022-45">&#91;45&#93;</a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Subsea_permafrost">Subsea permafrost</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=7" title="Edit section: Subsea permafrost" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=7" title="Edit section&#039;s source code: Subsea permafrost"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Sayedi_2020_subsea_projections.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/02/Sayedi_2020_subsea_projections.jpg/220px-Sayedi_2020_subsea_projections.jpg" decoding="async" width="220" height="173" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/02/Sayedi_2020_subsea_projections.jpg/330px-Sayedi_2020_subsea_projections.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/02/Sayedi_2020_subsea_projections.jpg/440px-Sayedi_2020_subsea_projections.jpg 2x" data-file-width="575" data-file-height="452" /></a><figcaption>Carbon dioxide and methane (in CO<sub style="font-size: 80%;vertical-align: -0.35em">2</sub> equivalent) emissions from subsea permafrost alone under the different <a href="/wiki/Representative_Concentration_Pathway" title="Representative Concentration Pathway">Representative Concentration Pathway</a> scenarios over time.<sup id="cite_ref-:4_49-0" class="reference"><a href="#cite_note-:4-49">&#91;49&#93;</a></sup></figcaption></figure> <p>Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions.<sup id="cite_ref-50" class="reference"><a href="#cite_note-50">&#91;50&#93;</a></sup> Thus, it can be defined as "the unglaciated continental shelf areas exposed during the <a href="/wiki/Last_Glacial_Maximum" title="Last Glacial Maximum">Last Glacial Maximum</a> (LGM, ~26 500 BP) that are currently inundated". Large stocks of organic matter (OM) and methane (<style data-mw-deduplicate="TemplateStyles:r1123817410">.mw-parser-output .template-chem2-su{display:inline-block;font-size:80%;line-height:1;vertical-align:-0.35em}.mw-parser-output .template-chem2-su>span{display:block;text-align:left}.mw-parser-output sub.template-chem2-sub{font-size:80%;vertical-align:-0.35em}.mw-parser-output sup.template-chem2-sup{font-size:80%;vertical-align:0.65em}</style><span class="chemf nowrap">CH<sub class="template-chem2-sub">4</sub></span>) are accumulated below and within the subsea permafrost deposits.This source of methane is different from <a href="/wiki/Methane_clathrate" title="Methane clathrate">methane clathrates</a>, but contributes to the overall outcome and feedbacks in the Earth's climate system.<sup id="cite_ref-:4_49-1" class="reference"><a href="#cite_note-:4-49">&#91;49&#93;</a></sup> </p><p>The size of today's subsea permafrost has been estimated at 2 million km² (~1/5 of the terrestrial permafrost domain size), which constitutes a 30–50% reduction since the LGM. Containing around 560 GtC in OM and 45 GtC in CH₄, with a current release of 18 and 38 MtC per year respectively, which is due to the warming and thawing that the subsea permafrost domain has been experiencing since after the LGM (~14000 years ago). In fact, because the subsea permafrost systems responds at millennial timescales to climate warming, the current carbon fluxes it is emitting to the water are in response to climatic changes occurring after the LGM. Therefore, human-driven climate change effects on subsea permafrost will only be seen hundreds or thousands of years from today. According to predictions under a business-as-usual emissions scenario <a href="/wiki/RCP8.5" class="mw-redirect" title="RCP8.5">RCP 8.5</a>, by 2100, 43 GtC could be released from the subsea permafrost domain, and 190 GtC by the year 2300. Whereas for the low emissions scenario RCP 2.6, 30% less emissions are estimated. This constitutes a significant anthropogenic-driven acceleration of carbon release in the upcoming centuries.<sup id="cite_ref-:4_49-2" class="reference"><a href="#cite_note-:4-49">&#91;49&#93;</a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Cumulative">Cumulative</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=8" title="Edit section: Cumulative" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=8" title="Edit section&#039;s source code: Cumulative"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In 2011, preliminary computer analyses suggested that permafrost emissions could be equivalent to around 15% of anthropogenic emissions.<sup id="cite_ref-51" class="reference"><a href="#cite_note-51">&#91;51&#93;</a></sup> </p><p>A 2018 perspectives article discussing <a href="/wiki/Tipping_points_in_the_climate_system" title="Tipping points in the climate system">tipping points in the climate system</a> activated around 2&#160;°C (3.6&#160;°F) of global warming suggested that at this threshold, permafrost thaw would add a further 0.09&#160;°C (0.16&#160;°F) to global temperatures by 2100, with a range of 0.04–0.16&#160;°C (0.072–0.288&#160;°F)<sup id="cite_ref-52" class="reference"><a href="#cite_note-52">&#91;52&#93;</a></sup> In 2021, another study estimated that in a future where <a href="/wiki/Net_zero" class="mw-redirect" title="Net zero">zero emissions</a> were reached following an emission of a further 1000 Pg C into the atmosphere (a scenario where temperatures ordinarily stay stable after the last emission, or start to decline slowly) permafrost carbon would add 0.06&#160;°C (0.11&#160;°F) (with a range of 0.02–0.14&#160;°C (0.036–0.252&#160;°F)) 50 years after the last anthropogenic emission, 0.09&#160;°C (0.16&#160;°F) (0.04–0.21&#160;°C (0.072–0.378&#160;°F)) 100 years later and 0.27&#160;°C (0.49&#160;°F) (0.12–0.49&#160;°C (0.22–0.88&#160;°F)) 500 years later.<sup id="cite_ref-53" class="reference"><a href="#cite_note-53">&#91;53&#93;</a></sup> However, neither study was able to take abrupt thaw into account. </p><p>In 2020, a study of the northern permafrost peatlands (a smaller subset of the entire permafrost area, covering 3.7 million km² out of the estimated 18 million km²<sup id="cite_ref-:4_49-3" class="reference"><a href="#cite_note-:4-49">&#91;49&#93;</a></sup>) would amount to ~1% of anthropogenic <a href="/wiki/Radiative_forcing" title="Radiative forcing">radiative forcing</a> by 2100, and that this proportion remains the same in all warming scenarios considered, from 1.5&#160;°C (2.7&#160;°F) to 6&#160;°C (11&#160;°F). It had further suggested that after 200 more years, those peatlands would have absorbed more carbon than what they had emitted into the atmosphere.<sup id="cite_ref-Hugelius2020_11-1" class="reference"><a href="#cite_note-Hugelius2020-11">&#91;11&#93;</a></sup> </p><p>The <a href="/wiki/IPCC_Sixth_Assessment_Report" title="IPCC Sixth Assessment Report">IPCC Sixth Assessment Report</a> estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per 1&#160;°C (1.8&#160;°F) of warming.<sup id="cite_ref-AR6_WG1_Chapter922_15-4" class="reference"><a href="#cite_note-AR6_WG1_Chapter922-15">&#91;15&#93;</a></sup><sup class="reference nowrap"><span title="Page / location: 1237">&#58;&#8202;1237&#8202;</span></sup> For comparison, by 2019, <i>annual</i> anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes.<sup id="cite_ref-AR6_WG1_Chapter922_15-5" class="reference"><a href="#cite_note-AR6_WG1_Chapter922-15">&#91;15&#93;</a></sup><sup class="reference nowrap"><span title="Page / location: 1237">&#58;&#8202;1237&#8202;</span></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Schuur_2022_century-scale_permafrost_projections.jpeg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7b/Schuur_2022_century-scale_permafrost_projections.jpeg/220px-Schuur_2022_century-scale_permafrost_projections.jpeg" decoding="async" width="220" height="150" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7b/Schuur_2022_century-scale_permafrost_projections.jpeg/330px-Schuur_2022_century-scale_permafrost_projections.jpeg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/7b/Schuur_2022_century-scale_permafrost_projections.jpeg/440px-Schuur_2022_century-scale_permafrost_projections.jpeg 2x" data-file-width="3383" data-file-height="2313" /></a><figcaption>Nine probable scenarios of <a href="/wiki/Greenhouse_gas_emission" class="mw-redirect" title="Greenhouse gas emission">greenhouse gas emissions</a> from permafrost thaw during the 21st century, which show a limited, moderate and intense CO<sub style="font-size: 80%;vertical-align: -0.35em">2</sub> and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">CH<sub class="template-chem2-sub">4</sub></span> emission response to low, medium and high-emission <a href="/wiki/Representative_Concentration_Pathway" title="Representative Concentration Pathway">Representative Concentration Pathways</a>. The vertical bar uses emissions of selected large countries as a comparison: the right-hand side of the scale shows their cumulative emissions since the start of the <a href="/wiki/Industrial_Revolution" title="Industrial Revolution">Industrial Revolution</a>, while the left-hand side shows each country's cumulative emissions for the rest of the 21st century if they remained unchanged from their 2019 levels.<sup id="cite_ref-Schuur2022_1-2" class="reference"><a href="#cite_note-Schuur2022-1">&#91;1&#93;</a></sup></figcaption></figure> <p>A 2021 assessment of the economic impact of climate tipping points estimated that permafrost carbon emissions would increase the <a href="/wiki/Social_cost_of_carbon" title="Social cost of carbon">social cost of carbon</a> by about 8.4% <sup id="cite_ref-54" class="reference"><a href="#cite_note-54">&#91;54&#93;</a></sup> However, the methods of that assessment have attracted controversy: when researchers like <a href="/wiki/Steve_Keen" title="Steve Keen">Steve Keen</a> and <a href="/wiki/Timothy_Lenton" class="mw-redirect" title="Timothy Lenton">Timothy Lenton</a> had accused it of underestimating the overall impact of tipping points and of higher levels of warming in general,<sup id="cite_ref-55" class="reference"><a href="#cite_note-55">&#91;55&#93;</a></sup> the authors have conceded some of their points.<sup id="cite_ref-56" class="reference"><a href="#cite_note-56">&#91;56&#93;</a></sup> </p><p>In 2021, a group of prominent permafrost researchers like <a href="/wiki/Merritt_Turetsky" title="Merritt Turetsky">Merritt Turetsky</a> had presented their collective estimate of permafrost emissions, including the abrupt thaw processes, as part of an effort to advocate for a 50% reduction in anthropogenic emissions by 2030 as a necessary milestone to help reach net zero by 2050. Their figures for combined permafrost emissions by 2100 amounted to 150–200 billion tonnes of carbon dioxide equivalent under 1.5&#160;°C (2.7&#160;°F) of warming, 220–300 billion tonnes under 2&#160;°C (3.6&#160;°F) and 400–500 billion tonnes if the warming was allowed to exceed 4&#160;°C (7.2&#160;°F). They compared those figures to the extrapolated present-day emissions of <a href="/wiki/Canada" title="Canada">Canada</a>, the <a href="/wiki/European_Union" title="European Union">European Union</a> and the <a href="/wiki/United_States" title="United States">United States</a> or <a href="/wiki/China" title="China">China</a>, respectively. The 400–500 billion tonnes figure would also be equivalent to the today's remaining budget for staying within a 1.5&#160;°C (2.7&#160;°F) target.<sup id="cite_ref-57" class="reference"><a href="#cite_note-57">&#91;57&#93;</a></sup> One of the scientists involved in that effort, <a href="/wiki/Susan_M._Natali" title="Susan M. Natali">Susan M. Natali</a> of <a href="/wiki/Woods_Hole_Research_Centre" class="mw-redirect" title="Woods Hole Research Centre">Woods Hole Research Centre</a>, had also led the publication of a complementary estimate in a <a href="/wiki/PNAS" class="mw-redirect" title="PNAS">PNAS</a> paper that year, which suggested that when the amplification of permafrost emissions by abrupt thaw and wildfires is combined with the foreseeable range of near-future anthropogenic emissions, avoiding the exceedance (or "overshoot") of 1.5&#160;°C (2.7&#160;°F) warming is already implausible, and the efforts to attain it may have to rely on <a href="/wiki/Carbon_dioxide_removal" title="Carbon dioxide removal">negative emissions</a> to force the temperature back down.<sup id="cite_ref-58" class="reference"><a href="#cite_note-58">&#91;58&#93;</a></sup> </p><p>An updated 2022 assessment of climate tipping points concluded that abrupt permafrost thaw would add 50% to gradual thaw rates, and would add 14 billion tons of carbon dioxide equivalent emissions by 2100 and 35 billion tons by 2300 per every degree of warming. This would have a warming impact of 0.04&#160;°C (0.072&#160;°F) per every full degree of warming by 2100, and 0.11&#160;°C (0.20&#160;°F) per every full degree of warming by 2300. It also suggested that at between 3&#160;°C (5.4&#160;°F) and 6&#160;°C (11&#160;°F) degrees of warming (with the most likely figure around 4&#160;°C (7.2&#160;°F) degrees) a large-scale collapse of permafrost areas could become irreversible, adding between 175 and 350 billion tons of <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1123817410"><span class="chemf nowrap">CO<sub class="template-chem2-sub">2</sub></span> equivalent emissions, or 0.2–0.4&#160;°C (0.36–0.72&#160;°F) degrees, over about 50 years (with a range between 10 and 300 years).<sup id="cite_ref-59" class="reference"><a href="#cite_note-59">&#91;59&#93;</a></sup><sup id="cite_ref-60" class="reference"><a href="#cite_note-60">&#91;60&#93;</a></sup> </p><p>A major review published in the year 2022 concluded that if the goal of preventing 2&#160;°C (3.6&#160;°F) of warming was realized, then the average annual permafrost emissions throughout the 21st century would be equivalent to the year 2019 annual emissions of <a href="/wiki/Russia" title="Russia">Russia</a>. Under RCP4.5, a scenario considered close to the current trajectory and where the warming stays slightly below 3&#160;°C (5.4&#160;°F), annual permafrost emissions would be comparable to year 2019 emissions of <a href="/wiki/Western_Europe" title="Western Europe">Western Europe</a> or the <a href="/wiki/United_States" title="United States">United States</a>, while under the scenario of high global warming and worst-case permafrost feedback response, they would nearly match year 2019 emissions of <a href="/wiki/China" title="China">China</a>.<sup id="cite_ref-Schuur2022_1-3" class="reference"><a href="#cite_note-Schuur2022-1">&#91;1&#93;</a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=9" title="Edit section: See also" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=9" title="Edit section&#039;s source code: See also"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Fire_and_carbon_cycling_in_boreal_forests" title="Fire and carbon cycling in boreal forests">Fire and carbon cycling in boreal forests</a></li> <li><a href="/wiki/Carbon_cycle" title="Carbon cycle">Carbon cycle</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=10" title="Edit section: References" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=10" title="Edit section&#039;s source code: References"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1217336898">.mw-parser-output .reflist{font-size:90%;margin-bottom:0.5em;list-style-type:decimal}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist 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a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a{background-size:contain}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a{background-size:contain}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:#d33}.mw-parser-output .cs1-visible-error{color:#d33}.mw-parser-output .cs1-maint{display:none;color:#2C882D;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911F}html.skin-theme-clientpref-night .mw-parser-output .cs1-visible-error,html.skin-theme-clientpref-night .mw-parser-output .cs1-hidden-error{color:#f8a397}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-visible-error,html.skin-theme-clientpref-os .mw-parser-output .cs1-hidden-error{color:#f8a397}html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911F}}</style><cite id="CITEREFSchuurAbbottCommaneErnakovich2022" class="citation journal cs1">Schuur, Edward A.G.; Abbott, Benjamin W.; Commane, Roisin; Ernakovich, Jessica; Euskirchen, Eugenie; Hugelius, Gustaf; Grosse, Guido; Jones, Miriam; Koven, Charlie; Leshyk, Victor; Lawrence, David; Loranty, Michael M.; Mauritz, Marguerite; Olefeldt, David; Natali, Susan; Rodenhizer, Heidi; Salmon, Verity; Schädel, Christina; Strauss, Jens; Treat, Claire; Turetsky, Merritt (2022). 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B.; Hanley, Brian P.; Grasselli, Matheus (19 May 2022). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9173761">"Estimates of economic and environmental damages from tipping points cannot be reconciled with the scientific literature"</a>. <i>Proceedings of the National Academy of Sciences</i>. <b>119</b> (21): e2117308119. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2022PNAS..11917308K">2022PNAS..11917308K</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1073%2Fpnas.2117308119">10.1073/pnas.2117308119</a></span>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a>&#160;<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9173761">9173761</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a>&#160;<a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/35588449">35588449</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a>&#160;<a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:248917625">248917625</a>.</cite><span title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences&amp;rft.atitle=Estimates+of+economic+and+environmental+damages+from+tipping+points+cannot+be+reconciled+with+the+scientific+literature&amp;rft.volume=119&amp;rft.issue=21&amp;rft.pages=e2117308119&amp;rft.date=2022-05-19&amp;rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC9173761%23id-name%3DPMC&amp;rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A248917625%23id-name%3DS2CID&amp;rft_id=info%3Abibcode%2F2022PNAS..11917308K&amp;rft_id=info%3Apmid%2F35588449&amp;rft_id=info%3Adoi%2F10.1073%2Fpnas.2117308119&amp;rft.aulast=Keen&amp;rft.aufirst=Steve&amp;rft.au=Lenton%2C+Timothy+M.&amp;rft.au=Garrett%2C+Timothy+J.&amp;rft.au=Rae%2C+James+W.+B.&amp;rft.au=Hanley%2C+Brian+P.&amp;rft.au=Grasselli%2C+Matheus&amp;rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC9173761&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3APermafrost+carbon+cycle" class="Z3988"></span></span> </li> <li id="cite_note-56"><span class="mw-cite-backlink"><b><a href="#cite_ref-56">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1215172403"><cite id="CITEREFDietzRisingStoerkWagner2022" class="citation journal cs1">Dietz, Simon; 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Retrieved <span class="nowrap">8 October</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=unknown&amp;rft.jtitle=50x30&amp;rft.atitle=Carbon+Emissions+from+Permafrost&amp;rft.date=2021&amp;rft_id=https%3A%2F%2Fwww.50x30.net%2Fcarbon-emissions-from-permafrost&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3APermafrost+carbon+cycle" class="Z3988"></span></span> </li> <li id="cite_note-58"><span class="mw-cite-backlink"><b><a href="#cite_ref-58">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1215172403"><cite id="CITEREFNataliHoldrenRogersTreharne2020" class="citation journal cs1">Natali, Susan M.; Holdren, John P.; Rogers, Brendan M.; Treharne, Rachael; Duffy, Philip B.; Pomerance, Rafe; MacDonald, Erin (10 December 2020). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8166174">"Permafrost carbon feedbacks threaten global climate goals"</a>. <i>Biological Sciences</i>. <b>118</b> (21). <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1073%2Fpnas.2100163118">10.1073/pnas.2100163118</a></span>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a>&#160;<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8166174">8166174</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a>&#160;<a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/34001617">34001617</a>.</cite><span title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.jtitle=Biological+Sciences&amp;rft.atitle=Permafrost+carbon+feedbacks+threaten+global+climate+goals&amp;rft.volume=118&amp;rft.issue=21&amp;rft.date=2020-12-10&amp;rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC8166174%23id-name%3DPMC&amp;rft_id=info%3Apmid%2F34001617&amp;rft_id=info%3Adoi%2F10.1073%2Fpnas.2100163118&amp;rft.aulast=Natali&amp;rft.aufirst=Susan+M.&amp;rft.au=Holdren%2C+John+P.&amp;rft.au=Rogers%2C+Brendan+M.&amp;rft.au=Treharne%2C+Rachael&amp;rft.au=Duffy%2C+Philip+B.&amp;rft.au=Pomerance%2C+Rafe&amp;rft.au=MacDonald%2C+Erin&amp;rft_id=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC8166174&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3APermafrost+carbon+cycle" class="Z3988"></span></span> </li> <li id="cite_note-59"><span class="mw-cite-backlink"><b><a href="#cite_ref-59">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1215172403"><cite id="CITEREFArmstrong_McKayAbramsWinkelmannSakschewski2022" class="citation journal cs1">Armstrong McKay, David; Abrams, Jesse; Winkelmann, Ricarda; Sakschewski, Boris; Loriani, Sina; Fetzer, Ingo; Cornell, Sarah; Rockström, Johan; Staal, Arie; Lenton, Timothy (9 September 2022). <a rel="nofollow" class="external text" href="https://www.science.org/doi/10.1126/science.abn7950">"Exceeding 1.5°C global warming could trigger multiple climate tipping points"</a>. <i>Science</i>. <b>377</b> (6611): eabn7950. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1126%2Fscience.abn7950">10.1126/science.abn7950</a>. <a href="/wiki/Hdl_(identifier)" class="mw-redirect" title="Hdl (identifier)">hdl</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://hdl.handle.net/10871%2F131584">10871/131584</a></span>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a>&#160;<a rel="nofollow" class="external text" href="https://www.worldcat.org/issn/0036-8075">0036-8075</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a>&#160;<a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/36074831">36074831</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a>&#160;<a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:252161375">252161375</a>.</cite><span title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=article&amp;rft.jtitle=Science&amp;rft.atitle=Exceeding+1.5%C2%B0C+global+warming+could+trigger+multiple+climate+tipping+points&amp;rft.volume=377&amp;rft.issue=6611&amp;rft.pages=eabn7950&amp;rft.date=2022-09-09&amp;rft_id=info%3Ahdl%2F10871%2F131584&amp;rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A252161375%23id-name%3DS2CID&amp;rft_id=info%3Adoi%2F10.1126%2Fscience.abn7950&amp;rft.issn=0036-8075&amp;rft_id=info%3Apmid%2F36074831&amp;rft.aulast=Armstrong+McKay&amp;rft.aufirst=David&amp;rft.au=Abrams%2C+Jesse&amp;rft.au=Winkelmann%2C+Ricarda&amp;rft.au=Sakschewski%2C+Boris&amp;rft.au=Loriani%2C+Sina&amp;rft.au=Fetzer%2C+Ingo&amp;rft.au=Cornell%2C+Sarah&amp;rft.au=Rockstr%C3%B6m%2C+Johan&amp;rft.au=Staal%2C+Arie&amp;rft.au=Lenton%2C+Timothy&amp;rft_id=https%3A%2F%2Fwww.science.org%2Fdoi%2F10.1126%2Fscience.abn7950&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3APermafrost+carbon+cycle" class="Z3988"></span></span> </li> <li id="cite_note-60"><span class="mw-cite-backlink"><b><a href="#cite_ref-60">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1215172403"><cite id="CITEREFArmstrong_McKay2022" class="citation web cs1">Armstrong McKay, David (9 September 2022). <a rel="nofollow" class="external text" href="https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/">"Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer"</a>. <i>climatetippingpoints.info</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2 October</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=unknown&amp;rft.jtitle=climatetippingpoints.info&amp;rft.atitle=Exceeding+1.5%C2%B0C+global+warming+could+trigger+multiple+climate+tipping+points+%E2%80%93+paper+explainer&amp;rft.date=2022-09-09&amp;rft.aulast=Armstrong+McKay&amp;rft.aufirst=David&amp;rft_id=https%3A%2F%2Fclimatetippingpoints.info%2F2022%2F09%2F09%2Fclimate-tipping-points-reassessment-explainer%2F&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3APermafrost+carbon+cycle" class="Z3988"></span></span> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;veaction=edit&amp;section=11" title="Edit section: External links" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Permafrost_carbon_cycle&amp;action=edit&amp;section=11" title="Edit section&#039;s source code: External links"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="http://ipa.arcticportal.org/">International Permafrost Association</a></li> <li><a rel="nofollow" class="external text" href="http://cenperm.ku.dk//">Center for Permafrost</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20101124144710/http://science.nasa.gov/missions/carve/">Carbon in Arctic Reservoirs Vulnerability Experiment</a></li></ul> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1228936124">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid 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href="/wiki/Greenhouse_gas_emissions" title="Greenhouse gas emissions">Greenhouse gas emissions</a> <ul><li><a href="/wiki/Carbon_accounting" title="Carbon accounting">Carbon accounting</a></li> <li><a href="/wiki/Carbon_footprint" title="Carbon footprint">Carbon footprint</a></li> <li><a href="/wiki/Carbon_leakage" title="Carbon leakage">Carbon leakage</a></li> <li><a href="/wiki/Greenhouse_gas_emissions_from_agriculture" title="Greenhouse gas emissions from agriculture">from agriculture</a></li> <li><a href="/wiki/Greenhouse_gas_emissions_from_wetlands" title="Greenhouse gas emissions from wetlands">from wetlands</a></li></ul></li> <li><a href="/wiki/World_energy_supply_and_consumption" title="World energy supply and consumption">World energy supply and consumption</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="History" style="font-size:114%;margin:0 4em">History</div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/History_of_climate_change_policy_and_politics" title="History of climate change policy and politics">History of climate change policy and politics</a></li> <li><a href="/wiki/History_of_climate_change_science" title="History of climate change science">History of climate change science</a></li> <li><a href="/wiki/Svante_Arrhenius" title="Svante Arrhenius">Svante Arrhenius</a></li> <li><a href="/wiki/James_Hansen" title="James Hansen">James Hansen</a></li> <li><a href="/wiki/Charles_David_Keeling" title="Charles David Keeling">Charles David Keeling</a></li> <li><a href="/wiki/United_Nations_Climate_Change_conference" class="mw-redirect" title="United Nations Climate Change conference">United Nations Climate Change conferences</a></li> <li>Years in climate change <ul><li><a href="/wiki/2019_in_climate_change" title="2019 in climate change">2019</a></li> <li><a href="/wiki/2020_in_climate_change" title="2020 in climate change">2020</a></li> <li><a href="/wiki/2021_in_climate_change" title="2021 in climate change">2021</a></li> <li><a href="/wiki/2022_in_climate_change" title="2022 in climate change">2022</a></li> <li><a href="/wiki/2023_in_climate_change" title="2023 in climate change">2023</a></li> <li><a href="/wiki/2024_in_climate_change" title="2024 in climate change">2024</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Effects_and_issues" style="font-size:114%;margin:0 4em"><a href="/wiki/Effects_of_climate_change" title="Effects of climate change">Effects and issues</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:10.25em">Physical</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Abrupt_climate_change" title="Abrupt climate change">Abrupt climate change</a></li> <li><a href="/wiki/Anoxic_event" title="Anoxic event">Anoxic event</a></li> <li><a href="/wiki/Arctic_methane_emissions" title="Arctic methane emissions">Arctic methane emissions</a></li> <li><a href="/wiki/Arctic_sea_ice_decline" title="Arctic sea ice decline">Arctic sea ice decline</a></li> <li><a href="/wiki/Atlantic_meridional_overturning_circulation" title="Atlantic meridional overturning circulation">Atlantic meridional overturning circulation</a></li> <li><a href="/wiki/Drought" title="Drought">Drought</a></li> <li><a href="/wiki/Extreme_weather" title="Extreme weather">Extreme weather</a></li> <li><a href="/wiki/Flood" title="Flood">Flood</a> <ul><li><a href="/wiki/Coastal_flooding" title="Coastal flooding">Coastal flooding</a></li></ul></li> <li><a href="/wiki/Heat_wave" title="Heat wave">Heat wave</a> <ul><li><a href="/wiki/Marine_heatwave" title="Marine heatwave">Marine</a></li> <li><a href="/wiki/Urban_heat_island" title="Urban heat island">Urban heat island</a></li></ul></li> <li><a href="/wiki/Effects_of_climate_change_on_oceans" title="Effects of climate change on oceans">Oceans</a> <ul><li><a href="/wiki/Ocean_acidification" title="Ocean acidification">acidification</a></li> <li><a href="/wiki/Ocean_deoxygenation" title="Ocean deoxygenation">deoxygenation</a></li> <li><a href="/wiki/Ocean_heat_content" title="Ocean heat content">heat content</a></li> <li><a href="/wiki/Sea_surface_temperature" title="Sea surface temperature">sea surface temperature</a></li> <li><a href="/wiki/Ocean_stratification" title="Ocean stratification">stratification</a></li> <li><a href="/wiki/Ocean_temperature" title="Ocean temperature">temperature</a></li></ul></li> <li><a href="/wiki/Ozone_depletion" title="Ozone depletion">Ozone depletion</a></li> <li><a href="/wiki/Permafrost#Impacts_of_climate_change" title="Permafrost">Permafrost thaw</a></li> <li><a href="/wiki/Retreat_of_glaciers_since_1850" title="Retreat of glaciers since 1850">Retreat of glaciers since 1850</a></li> <li><a href="/wiki/Sea_level_rise" title="Sea level rise">Sea level rise</a></li> <li><a href="/wiki/Season_creep" title="Season creep">Season creep</a></li> <li><a href="/wiki/Tipping_points_in_the_climate_system" title="Tipping points in the climate system">Tipping points in the climate system</a></li> <li><a href="/wiki/Tropical_cyclones_and_climate_change" title="Tropical cyclones and climate change">Tropical cyclones</a></li> <li><a href="/wiki/Effects_of_climate_change_on_the_water_cycle" title="Effects of climate change on the water cycle">Water cycle</a></li> <li><a href="/wiki/Climate_change_and_wildfires" class="mw-redirect" title="Climate change and wildfires">Wildfires</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Flora and fauna</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Effects_of_climate_change_on_biomes" title="Effects of climate change on biomes">Biomes</a> <ul><li><a href="/wiki/Mass_mortality_event" title="Mass mortality event">Mass mortality event</a></li></ul></li> <li><a href="/wiki/Climate_change_and_birds" title="Climate change and birds">Birds</a></li> <li><a href="/wiki/Extinction_risk_from_climate_change" title="Extinction risk from climate change">Extinction risk</a></li> <li><a href="/wiki/Forest_dieback" title="Forest dieback">Forest dieback</a></li> <li><a href="/wiki/Climate_change_and_invasive_species" title="Climate change and invasive species">Invasive species</a></li> <li><a href="/wiki/Human_impact_on_marine_life#Climate_change" title="Human impact on marine life">Marine life</a></li> <li><a href="/wiki/Effects_of_climate_change_on_plant_biodiversity" title="Effects of climate change on plant biodiversity">Plant biodiversity</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Social and economic</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Effects_of_climate_change_on_agriculture" title="Effects of climate change on agriculture">Agriculture</a> <ul><li><a href="/wiki/Effects_of_climate_change_on_livestock" title="Effects of climate change on livestock">Livestock</a></li> <li><a href="/wiki/Climate_change_and_agriculture_in_the_United_States" title="Climate change and agriculture in the United States">United States</a></li></ul></li> <li><a href="/wiki/Climate_change_and_children" title="Climate change and children">Children</a></li> <li><a href="/wiki/Climate_change_and_cities" title="Climate change and cities">Cities</a></li> <li><a href="/wiki/Climate_change_and_civilizational_collapse" title="Climate change and civilizational collapse">Civilizational collapse</a></li> <li><a href="/wiki/Disability_and_climate_change" title="Disability and climate change">Disability</a></li> <li><a href="/wiki/Economic_analysis_of_climate_change" title="Economic analysis of climate change">Economic impacts</a> <ul><li><a href="/wiki/Climate_change_and_insurance_in_the_United_States" title="Climate change and insurance in the United States">U.S. insurance industry</a></li></ul></li> <li><a href="/wiki/Climate_change_and_fisheries" title="Climate change and fisheries">Fisheries</a></li> <li><a href="/wiki/Climate_change_and_gender" title="Climate change and gender">Gender</a></li> <li><a href="/wiki/Effects_of_climate_change_on_human_health" title="Effects of climate change on human health">Health</a> <ul><li><a href="/wiki/Effects_of_climate_change_on_mental_health" title="Effects of climate change on mental health">Mental health</a></li></ul></li> <li><a href="/wiki/Human_rights_and_climate_change" title="Human rights and climate change">Human rights</a></li> <li><a href="/wiki/Climate_change_and_Indigenous_peoples" class="mw-redirect" title="Climate change and Indigenous peoples">Indigenous peoples</a></li> <li><a href="/wiki/Climate_change_and_infectious_diseases" title="Climate change and infectious diseases">Infectious diseases</a></li> <li><a href="/wiki/Climate_migration" title="Climate migration">Migration</a></li> <li><a href="/wiki/Climate_change_and_poverty" title="Climate change and poverty">Poverty</a></li> <li><a href="/wiki/Psychological_impact_of_climate_change" title="Psychological impact of climate change">Psychological impacts</a></li> <li><a href="/wiki/Climate_security" title="Climate security">Security and conflict</a></li> <li><a href="/wiki/Urban_flooding" title="Urban flooding">Urban flooding</a></li> <li><a href="/wiki/Water_scarcity" title="Water scarcity">Water scarcity</a></li> <li><a href="/wiki/Water_security" title="Water security">Water security</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em"><a href="/wiki/Template:Climate_change_regions" title="Template:Climate change regions">By country and region</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Climate_change_in_Africa" title="Climate change in Africa">Africa</a></li> <li><a href="/wiki/Climate_change_in_the_Americas" title="Climate change in the Americas">Americas</a></li> <li><a href="/wiki/Climate_change_in_Antarctica" title="Climate change in Antarctica">Antarctica</a></li> <li><a href="/wiki/Climate_change_in_the_Arctic" title="Climate change in the Arctic">Arctic</a></li> <li><a href="/wiki/Climate_change_in_Asia" title="Climate change in Asia">Asia</a></li> <li><a href="/wiki/Climate_change_in_Australia" title="Climate change in Australia">Australia</a></li> <li><a href="/wiki/Climate_change_in_the_Caribbean" title="Climate change in the Caribbean">Caribbean</a></li> <li><a href="/wiki/Climate_change_in_Europe" title="Climate change in Europe">Europe</a></li> <li><a href="/wiki/Climate_change_in_the_Middle_East_and_North_Africa" title="Climate change in the Middle East and North Africa">Middle East and North Africa</a></li> <li><a href="/wiki/Effects_of_climate_change_on_small_island_countries" title="Effects of climate change on small island countries">Small island countries</a></li> <li><a href="/wiki/Category:Climate_change_by_country" title="Category:Climate change by country">by individual country</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Mitigation" style="font-size:114%;margin:0 4em"><a href="/wiki/Climate_change_mitigation" title="Climate change mitigation">Mitigation</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:10.25em"><a href="/wiki/Economic_analysis_of_climate_change" title="Economic analysis of climate change">Economics and finance</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Carbon_budget" title="Carbon budget">Carbon budget</a></li> <li><a href="/wiki/Carbon_emission_trading" title="Carbon emission trading">Carbon emission trading</a></li> <li><a href="/wiki/Carbon_offsets_and_credits" title="Carbon offsets and credits">Carbon offsets and credits</a> <ul><li><a href="/wiki/Gold_Standard_(carbon_offset_standard)" title="Gold Standard (carbon offset standard)">Gold Standard (carbon offset standard)</a></li></ul></li> <li><a href="/wiki/Carbon_price" title="Carbon price">Carbon price</a></li> <li><a href="/wiki/Carbon_tax" title="Carbon tax">Carbon tax</a></li> <li><a href="/wiki/Climate_debt" title="Climate debt">Climate debt</a></li> <li><a href="/wiki/Climate_finance" title="Climate finance">Climate finance</a></li> <li><a href="/wiki/Climate_risk_insurance" title="Climate risk insurance">Climate risk insurance</a></li> <li><a href="/wiki/Co-benefits_of_climate_change_mitigation" class="mw-redirect" title="Co-benefits of climate change mitigation">Co-benefits of climate change mitigation</a></li> <li><a href="/wiki/Economics_of_climate_change_mitigation" title="Economics of climate change mitigation">Economics of climate change mitigation</a></li> <li><a href="/wiki/Fossil_fuel_divestment" title="Fossil fuel divestment">Fossil fuel divestment</a></li> <li><a href="/wiki/Green_Climate_Fund" title="Green Climate Fund">Green Climate Fund</a></li> <li><a href="/wiki/Low-carbon_economy" title="Low-carbon economy">Low-carbon economy</a></li> <li><a href="/wiki/Net_zero_emissions" title="Net zero emissions">Net zero emissions</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Energy</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Carbon_capture_and_storage" title="Carbon capture and storage">Carbon capture and storage</a></li> <li><a href="/wiki/Energy_transition" title="Energy transition">Energy transition</a> <ul><li><a href="/wiki/Fossil_fuel_phase-out" title="Fossil fuel phase-out">Fossil fuel phase-out</a></li></ul></li> <li><a href="/wiki/Nuclear_power" title="Nuclear power">Nuclear power</a></li> <li><a href="/wiki/Renewable_energy" title="Renewable energy">Renewable energy</a></li> <li><a href="/wiki/Sustainable_energy" title="Sustainable energy">Sustainable energy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Preserving and enhancing<br /> <a href="/wiki/Carbon_sink" title="Carbon sink">carbon sinks</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Blue_carbon" title="Blue carbon">Blue carbon</a></li> <li><a href="/wiki/Carbon_dioxide_removal" title="Carbon dioxide removal">Carbon dioxide removal</a> <ul><li><a href="/wiki/Carbon_sequestration" title="Carbon sequestration">Carbon sequestration</a></li> <li><a href="/wiki/Direct_air_capture" title="Direct air capture">Direct air capture</a></li></ul></li> <li><a href="/wiki/Carbon_farming" title="Carbon farming">Carbon farming</a></li> <li><a href="/wiki/Climate-smart_agriculture" title="Climate-smart agriculture">Climate-smart agriculture</a></li> <li>Forest management <ul><li><a href="/wiki/Afforestation" title="Afforestation">afforestation</a></li> <li><a href="/wiki/Carbon_sequestration#Forestry" title="Carbon sequestration">forestry for carbon sequestration</a></li> <li><a href="/wiki/REDD_and_REDD%2B" title="REDD and REDD+">REDD and REDD+</a></li> <li><a href="/wiki/Reforestation" title="Reforestation">reforestation</a></li></ul></li> <li><a href="/wiki/Land_use,_land-use_change,_and_forestry" title="Land use, land-use change, and forestry">Land use, land-use change, and forestry</a> (LULUCF and AFOLU)</li> <li><a href="/wiki/Nature-based_solutions" title="Nature-based solutions">Nature-based solutions</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Personal</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Individual_action_on_climate_change" title="Individual action on climate change">Individual action on climate change</a> <ul><li><a href="/wiki/Plant-based_diet" title="Plant-based diet">Plant-based diet</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Society_and_adaptation" style="font-size:114%;margin:0 4em">Society and <a href="/wiki/Climate_change_adaptation" title="Climate change adaptation">adaptation</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:10.25em">Society</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Business_action_on_climate_change" title="Business action on climate change">Business action</a></li> <li><a href="/wiki/Climate_action" title="Climate action">Climate action</a></li> <li><a href="/wiki/Climate_emergency_declaration" title="Climate emergency declaration">Climate emergency declaration</a></li> <li><a href="/wiki/Climate_movement" title="Climate movement">Climate movement</a> <ul><li><a href="/wiki/School_Strike_for_Climate" title="School Strike for Climate">School Strike for Climate</a></li></ul></li> <li><a href="/wiki/Climate_change_denial" title="Climate change denial">Denial</a></li> <li><a href="/wiki/Ecological_grief" title="Ecological grief">Ecological grief</a></li> <li><a href="/wiki/Climate_governance" title="Climate governance">Governance</a></li> <li><a href="/wiki/Climate_justice" title="Climate justice">Justice</a></li> <li><a href="/wiki/Climate_change_litigation" title="Climate change litigation">Litigation</a></li> <li><a href="/wiki/Politics_of_climate_change" title="Politics of climate change">Politics</a></li> <li><a href="/wiki/Public_opinion_on_climate_change" title="Public opinion on climate change">Public opinion</a></li> <li><a href="/wiki/Women_in_climate_change" title="Women in climate change">Women</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em"><a href="/wiki/Climate_change_adaptation" title="Climate change adaptation">Adaptation</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Climate_change_adaptation_strategies_on_the_German_coast" title="Climate change adaptation strategies on the German coast">Adaptation strategies on the German coast</a></li> <li><a href="/wiki/Adaptive_capacity" title="Adaptive capacity">Adaptive capacity</a></li> <li><a href="/wiki/Disaster_risk_reduction" title="Disaster risk reduction">Disaster risk reduction</a></li> <li><a href="/wiki/Ecosystem-based_adaptation" title="Ecosystem-based adaptation">Ecosystem-based adaptation</a></li> <li><a href="/wiki/Flood_control" title="Flood control">Flood control</a></li> <li><a href="/wiki/Loss_and_damage_(climate_change)" title="Loss and damage (climate change)">Loss and damage</a></li> <li><a href="/wiki/Managed_retreat" title="Managed retreat">Managed retreat</a></li> <li><a href="/wiki/Nature-based_solutions" title="Nature-based solutions">Nature-based solutions</a></li> <li><a href="/wiki/Climate_resilience" title="Climate resilience">Resilience</a></li> <li><a href="/wiki/Climate_risk" title="Climate risk">Risk</a></li> <li><a href="/wiki/Climate_change_vulnerability" title="Climate change vulnerability">Vulnerability</a></li> <li><a href="/wiki/The_Adaptation_Fund" title="The Adaptation Fund">The Adaptation Fund</a></li> <li><a href="/wiki/National_Adaptation_Programme_of_Action" title="National Adaptation Programme of Action">National Adaptation Programme of Action</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em"><a href="/wiki/Climate_communication" title="Climate communication">Communication</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Climate_Change_Performance_Index" title="Climate Change Performance Index">Climate Change Performance Index</a></li> <li><a href="/wiki/Climate_crisis" title="Climate crisis">Climate crisis (term)</a></li> <li><a href="/wiki/Climate_spiral" title="Climate spiral">Climate spiral</a></li> <li><a href="/wiki/Climate_change_education" title="Climate change education">Education</a></li> <li><a href="/wiki/Media_coverage_of_climate_change" title="Media coverage of climate change">Media coverage</a></li> <li><a href="/wiki/Climate_change_in_popular_culture" title="Climate change in popular culture">Popular culture depictions</a> <ul><li><a href="/wiki/Climate_change_art" title="Climate change art">art</a></li> <li><a href="/wiki/Climate_fiction" title="Climate fiction">fiction</a></li> <li><a href="/wiki/List_of_climate_change_video_games" class="mw-redirect" title="List of climate change video games">video games</a></li></ul></li> <li><a href="/wiki/Warming_stripes" title="Warming stripes">Warming stripes</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">International agreements</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Glasgow_Climate_Pact" title="Glasgow Climate Pact">Glasgow Climate Pact</a></li> <li><a href="/wiki/Kyoto_Protocol" title="Kyoto Protocol">Kyoto Protocol</a></li> <li><a href="/wiki/Paris_Agreement" title="Paris Agreement">Paris Agreement</a> <ul><li><a href="/wiki/Cooperative_Mechanisms_under_Article_6_of_the_Paris_Agreement" title="Cooperative Mechanisms under Article 6 of the Paris Agreement">Cooperative Mechanisms under Article 6 of the Paris Agreement</a></li> <li><a href="/wiki/Nationally_determined_contribution" title="Nationally determined contribution">Nationally determined contributions</a></li></ul></li> <li><a href="/wiki/Sustainable_Development_Goal_13" title="Sustainable Development Goal 13">Sustainable Development Goal 13</a></li> <li><a href="/wiki/United_Nations_Framework_Convention_on_Climate_Change" title="United Nations Framework Convention on Climate Change">United Nations Framework Convention on Climate Change</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Background_and_theory" style="font-size:114%;margin:0 4em">Background and theory</div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:10.25em">Measurements</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Global_surface_temperature" title="Global surface temperature">Global surface temperature</a></li> <li><a href="/wiki/Instrumental_temperature_record" title="Instrumental temperature record">Instrumental temperature record</a></li> <li><a href="/wiki/Proxy_(climate)" title="Proxy (climate)">Proxy</a></li> <li><a href="/wiki/Satellite_temperature_measurement" title="Satellite temperature measurement">Satellite temperature measurement</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Theory</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Albedo" title="Albedo">Albedo</a></li> <li><a href="/wiki/Carbon_cycle" title="Carbon cycle">Carbon cycle</a> <ul><li><a href="/wiki/Atmospheric_carbon_cycle" title="Atmospheric carbon cycle">atmospheric</a></li> <li><a href="/wiki/Biological_pump" title="Biological pump">biologic</a></li> <li><a href="/wiki/Oceanic_carbon_cycle" title="Oceanic carbon cycle">oceanic</a></li> <li><a class="mw-selflink selflink">permafrost</a></li></ul></li> <li><a href="/wiki/Carbon_sink" title="Carbon sink">Carbon sink</a></li> <li><a href="/wiki/Climate_sensitivity" title="Climate sensitivity">Climate sensitivity</a></li> <li><a href="/wiki/Climate_variability_and_change" title="Climate variability and change">Climate variability and change</a></li> <li><a href="/wiki/Cloud_feedback" title="Cloud feedback">Cloud feedback</a></li> <li><a href="/wiki/Cloud_forcing" class="mw-redirect" title="Cloud forcing">Cloud forcing</a> <ul><li><a href="/wiki/Fixed_anvil_temperature_hypothesis" title="Fixed anvil temperature hypothesis">Fixed anvil temperature hypothesis</a></li></ul></li> <li><a href="/wiki/Cryosphere" title="Cryosphere">Cryosphere</a></li> <li><a href="/wiki/Earth%27s_energy_budget" title="Earth&#39;s energy budget">Earth's energy budget</a></li> <li><a href="/wiki/Extreme_event_attribution" title="Extreme event attribution">Extreme event attribution</a></li> <li><a href="/wiki/Climate_change_feedbacks" title="Climate change feedbacks">Feedbacks</a></li> <li><a href="/wiki/Global_warming_potential" title="Global warming potential">Global warming potential</a></li> <li><a href="/wiki/Illustrative_model_of_greenhouse_effect_on_climate_change" title="Illustrative model of greenhouse effect on climate change">Illustrative model of greenhouse effect on climate change</a></li> <li><a href="/wiki/Orbital_forcing" title="Orbital forcing">Orbital forcing</a></li> <li><a href="/wiki/Radiative_forcing" title="Radiative forcing">Radiative forcing</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:10.25em">Research and modelling</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Climate_change_scenario" title="Climate change scenario">Climate change scenario</a></li> <li><a href="/wiki/Climate_model" title="Climate model">Climate model</a></li> <li><a href="/wiki/Coupled_Model_Intercomparison_Project" title="Coupled Model Intercomparison Project">Coupled Model Intercomparison Project</a></li> <li><a href="/wiki/Intergovernmental_Panel_on_Climate_Change" title="Intergovernmental Panel on Climate Change">Intergovernmental Panel on Climate Change (IPCC)</a> <ul><li><a href="/wiki/IPCC_Sixth_Assessment_Report" title="IPCC Sixth Assessment Report">IPCC Sixth Assessment Report</a></li></ul></li> <li><a href="/wiki/Paleoclimatology" title="Paleoclimatology">Paleoclimatology</a></li> <li><a href="/wiki/Paleotempestology" title="Paleotempestology">Paleotempestology</a></li> <li><a href="/wiki/Representative_Concentration_Pathway" title="Representative Concentration Pathway">Representative Concentration Pathway</a></li> <li><a href="/wiki/Shared_Socioeconomic_Pathways" title="Shared Socioeconomic Pathways">Shared Socioeconomic Pathways</a></li> <li><a href="/wiki/Solar_radiation_modification" title="Solar radiation modification">Solar radiation modification</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><b><span class="nowrap"><span class="noviewer" typeof="mw:File"><span><img alt="icon" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/Climate_change_icon.png/16px-Climate_change_icon.png" decoding="async" width="16" height="15" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/Climate_change_icon.png/24px-Climate_change_icon.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/66/Climate_change_icon.png/32px-Climate_change_icon.png 2x" data-file-width="1112" data-file-height="1056" /></span></span> </span><a href="/wiki/Portal:Climate_change" title="Portal:Climate change">Climate change&#32;portal</a></b></li> <li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <b><a href="/wiki/Category:Climate_change" title="Category:Climate change">Category</a></b></li> <li><span class="noviewer" typeof="mw:File"><span title="List-Class article"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/d/db/Symbol_list_class.svg/16px-Symbol_list_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/d/db/Symbol_list_class.svg/23px-Symbol_list_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/d/db/Symbol_list_class.svg/31px-Symbol_list_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <b><a href="/wiki/Glossary_of_climate_change" title="Glossary of climate change">Glossary</a></b></li> <li><span class="noviewer" typeof="mw:File"><span title="List-Class article"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/d/db/Symbol_list_class.svg/16px-Symbol_list_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/d/db/Symbol_list_class.svg/23px-Symbol_list_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/d/db/Symbol_list_class.svg/31px-Symbol_list_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <b><a href="/wiki/Index_of_climate_change_articles" title="Index of climate change articles">Index</a></b></li></ul> </div></td></tr></tbody></table></div></div>'