Editing IPCC:AR6/SR15/Chapter-3 (section)

== 3.5.5.3 Permafrost ==

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Widespread thawing of permafrost potentially makes a large carbon store (estimated to be twice the size of the atmospheric store; Dolman et al., 2010) <sup>[[#fn:r1234|1234]]</sup> vulnerable to decomposition, which could lead to further increases in atmospheric carbon dioxide and methane and hence to further global warming. This feedback loop between warming and the release of greenhouse gas from thawing tundra represents a potential tipping point. However, the carbon released to the atmosphere from thawing permafrost is projected to be restricted to 0.09–0.19 Gt C yr <sup>–1</sup> at 2°C of global warming and to 0.08–0.16 Gt C yr <sup>–1</sup> at 1.5°C (E.J. Burke et al., 2018) <sup>[[#fn:r1235|1235]]</sup> , which does not indicate a tipping point ( ''medium confidence'' ). At higher degrees of global warming, in the order of 3°C, a different type of tipping point in permafrost may be reached. A single model projection (Drijfhout et al., 2015) <sup>[[#fn:r1236|1236]]</sup> suggested that higher temperatures may induce a smaller ice fraction in soils in the tundra, leading to more rapidly warming soils and a positive feedback mechanism that results in permafrost collapse ( ''low confidence'' ). The disparity between the multi-millennial time scales of soil carbon accumulation and potentially rapid decomposition in a warming climate implies that the loss of this carbon to the atmosphere would be essentially irreversible (Collins et al., 2013) <sup>[[#fn:r1237|1237]]</sup> .

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