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

==== 3.6.3.3 Permafrost ====

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The slow rate of permafrost thaw introduces a lag between the transient degradation of near-surface permafrost and contemporary climate, so that the equilibrium response is expected to be 25–38% greater than the transient response simulated in climate models (Slater and Lawrence, 2013) <sup>[[#fn:r1376|1376]]</sup> . The long-term, equilibrium Arctic permafrost loss to global warming was analysed by Chadburn et al. (2017) <sup>[[#fn:r1377|1377]]</sup> . They used an empirical relation between recent mean annual air temperatures and the area underlain by permafrost coupled to Coupled Model Intercomparison Project Phase 5 (CMIP5) stabilization projections to 2300 for RCP2.6 and RCP4.5. Their estimate of the sensitivity of permafrost to warming is 2.9–5.0 million km <sup>2</sup> °C <sup>–1</sup> (1 standard deviation confidence interval), which suggests that stabilizing climate at 1.5°C as opposed to 2°C would reduce the area of eventual permafrost loss by 1.5 to 2.5 million km <sup>2</sup> (stabilizing at 56–83% as opposed to 43–72% of 1960–1990 levels). This work, combined with the assessment of Collins et al. (2013) <sup>[[#fn:r1378|1378]]</sup> on the link between global warming and permafrost loss, leads to the assessment that permafrost extent would be appreciably greater in a 1.5°C warmer world compared to in a 2°C warmer world ( ''low to medium confidence'' ).

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