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

===== 3.4.1.2.1 Temperature =====

Record high temperatures at ~10–20 m depth in the permafrost (near or below the depths affected by intra-annual fluctuation in temperature) have been documented at many long-term monitoring sites in the Northern Hemisphere circumpolar permafrost region (AMAP, 2017d <sup>[[#fn:r1386|1386]]</sup> ) (Figure 3.10) ( ''very high confidence'' ). At some locations, the temperature is 2°C–3°C higher than 30 years ago. During the decade between 2007 and 2016, the rate of increase in permafrost temperatures was 0.39°C ± 0.15°C for colder continuous zone permafrost monitoring sites, 0.20°C ± 0.10°C for warmer discontinuous zone permafrost, giving a global average of 0.29 ± 0.12°C across all polar and mountain permafrost (Biskaborn et al., 2019 <sup>[[#fn:r1387|1387]]</sup> ). Relatively smaller increases in permafrost temperature in warmer sites indicate that permafrost is thawing with heat absorbed by the ice-to-water phase change, and as a result, the active layer may be increasing in thickness. In contrast to temperature, there is only ''medium confidence'' that active layer thickness across the region has increased. This confidence level is because decadal trends vary across regions and sites (Shiklomanov et al., 2012 <sup>[[#fn:r1388|1388]]</sup> ) and because mechanical probing of the active layer can underestimate the degradation of permafrost in some cases because the surface subsides when ground ice melts and drains (Mekonnen et al., 2016 <sup>[[#fn:r1389|1389]]</sup> ; AMAP, 2017d <sup>[[#fn:r1390|1390]]</sup> ; Streletskiy et al., 2017 <sup>[[#fn:r1391|1391]]</sup> ). Permafrost in the Southern Hemisphere polar region occurs in ice-free exposed areas (Bockheim et al., 2013 <sup>[[#fn:r1392|1392]]</sup> ), 0.18% of the total land area of Antarctica (Burton-Johnson et al., 2016). This area is three orders of magnitude smaller than the 13–18 x 10 6 km 2 area underlain by permafrost in the Northern Hemisphere terrestrial permafrost region (Gruber, 2012). Antarctic permafrost temperatures are generally colder (Noetzli et al., 2017 <sup>[[#fn:r1403|1403]]</sup> ) and increased 0.37°C ± 0.10°C between 2007 and 2016 (Biskaborn et al., 2019 <sup>[[#fn:r1404|1404]]</sup> ).

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'''Figure 3.10'''

<span id="schematic-of-important-land-surface-components-influenced-by-the-arctic-terrestrial-cryosphere-permafrost-1-ground-ice-2-river-discharge-3-abrupt-thaw-4-surface-water-5-fire-6-tundra-7-shrubs-8-boreal-forest-9-lake-ice-10-seasonal-snow-11.-time-series-of-snow-cover-extent-anomalies-in-june-relative-to-19812010-climatology-from"></span>
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'''Schematic of important land surface components influenced by the Arctic terrestrial cryosphere: permafrost (1); ground ice (2); river discharge (3); abrupt thaw (4); surface water (5); fire (6); tundra (7); shrubs (8); boreal forest (9); lake ice (10); seasonal snow (11). Time series of snow cover extent anomalies in June (relative to 1981–2010 climatology) from […]'''
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[[File:1f09753851439dd6e693fe4f8198d24b IPCC-SROCC-CH_3_10.jpg]]

Schematic of important land surface components influenced by the Arctic terrestrial cryosphere: permafrost (1); ground ice (2); river discharge (3); abrupt thaw (4); surface water (5); fire (6); tundra (7); shrubs (8); boreal forest (9); lake ice (10); seasonal snow (11). Time series of snow cover extent anomalies in June (relative to 1981–2010 climatology) from 5 products based on the approach of Mudryk et al. (2017) (a); permafrost temperature change normalised to a baseline period (Romanovsky et al., 2017), Region A: Continuous to discontinuous permafrost in Scandanavia, Svalbard, and Russia/Siberia, Region B: Cold continuous permafrost in northern Alaska, Northwest Territories, and NE Siberia, Region C: Cold continuous permafrost in Eastern and High Arctic Canada, Region D: Discontinuous permafrost in Interior Alaska and Northwest Canada (b), and runoff from northern flowing watersheds normalised to a baseline period (1981–2010) (Holmes et al., 2018), multi-station average (± 1 standard deviation) (c). Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model average (± 1 standard deviation) projections for different Representative Concentration Pathway (RCP) scenarios for June snow cover extent change (based on Thackeray et al., 2016) (d), area change of near-surface permafrost (e), and runoff change to the Arctic Ocean (based on McGuire et al., 2018) (f).

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