Editing IPCC:AR6/SRCCL/Chapter-7 (section)

==== 7.2.2.7 Permafrost ====

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There is a risk of damage to the natural and built environment from permafrost thaw-related ground instability. Residential, transportation, and industrial infrastructure in the pan-Arctic permafrost area are particularly at risk (Hjort et al. 2018 <sup>[[#fn:r150|150]]</sup> ). ''High risks'' already exist at low temperatures ( ''high confidence'' ). Approximately, 21–37% of Arctic permafrost is projected to thaw under a 1.5°C of warming (Hoegh-Guldberg et al. 2018 <sup>[[#fn:r151|151]]</sup> ). This increases to ''very high risk'' around 2°C (between 1.8°C and 2.3°C) of temperature increase since pre-industrial times ( ''medium confidence'' ) with 35–47% of the Arctic permafrost thawing (Hoegh-Guldberg et al. 2018 <sup>[[#fn:r152|152]]</sup> ). If climate stabilised at 2°C, still approximately 40% of permafrost area would be lost (Chadburn et al. 2017 <sup>[[#fn:r153|153]]</sup> ), leading to nearly four million people and 70% of current infrastructure in the pan-Arctic permafrost area exposed to permafrost thaw and high hazard (Hjort et al. 2018 <sup>[[#fn:r154|154]]</sup> ). Indeed between 2°C and 3°C a collapse of permafrost may occur with a drastic biome shift from tundra to boreal forest (Drijfhout et al. 2015; SR15 <sup>[[#fn:r155|155]]</sup> ). There is mixed evidence of a tipping point in permafrost collapse, leading to enhanced greenhouse gas (GHG) emission – particularly methane – between 2°C and 3°C (Hoegh-Guldberg et al. 2018 <sup>[[#fn:r156|156]]</sup> ).

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