Editing IPCC:AR6/WGI/Chapter-9 (section)

=== Ice Sheets ===

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'''The Greenland Ice Sheet has lost 4890 [4140 to 5640] Gt mass over the period 199''' '''2–2''' '''020, equivalent to 13.5 [11.4 to 15.6] mm global mean sea level rise. The mass-loss rate was on average 39 [–3 to +80] Gt yr''' –1 '''over the period 199''' '''2–1''' '''999, 175 [131 to 220] Gt yr''' –1 '''over the period 200''' '''0–2''' '''009 and 243 [197 to 290] Gt yr''' –1 '''over the period 201''' '''0–2''' '''019.''' This mass loss is driven by both discharge and surface melt, with the latter increasingly becoming the dominating component of mass loss with high interannual variability in the last decade ( ''high confidence'' ). The largest mass losses occurred in the north-west and the south-east of Greenland ( ''high confidence'' ). {2.3.2, 9.4.1}

'''The Antarctic Ice Sheet has lost 2670 [1800 to 3540] Gt mass over the period 199''' '''2–2''' '''020, equivalent to 7.4 [5.0 to 9.8] mm global mean sea level rise. The mass-loss rate was, on average, 49 [–2 to +100] Gt yr''' –1 '''over the period 199''' '''2–1''' '''999, 70 [22 to 119] Gt yr''' –1 '''over the period 200''' '''0–2''' '''009 and 148 [94 to 202] Gt yr''' –1 '''over the period 201''' '''0–2''' '''019.''' Mass losses from West Antarctic outlet glaciers outpaced mass gain from increased snow accumulation on the continent and dominated the ice-sheet mass losses since 1992 ( ''very high confidence'' ). These mass losses from the West Antarctic outlet glaciers were mainly induced by ice-shelf basal melt ( ''high confidence'' ) and locally by ice-shelf disintegration preceded by strong surface melt ( ''high confidence'' ). Parts of the East Antarctic Ice Sheet have lost mass in the last two decades ( ''high confidence'' ). {2.3.2, 9.4.2, Atlas.11.1}

'''Both the Greenland Ice Sheet''' ( ''virtually certain'' ''') and the Antarctic Ice Sheet''' ( ''likely'' ''') will continue to lose mass throughout this century under all considered SSP scenarios. The related contribution to global mean sea level rise until 2100 from the Greenland Ice Sheet will''' ''likely'' '''be 0.01 to 0.10 m under SSP1-2.6, 0.04 to 0.13 m under SSP2-4.5 and 0.0''' '''9–0''' '''.18 m under SSP5-8.5, while the Antarctic Ice Sheet will''' ''likely'' '''contribute 0.03 to 0.27 m under SSP1-2.6, 0.03 to 0.29 m under SSP2-4.5, and 0.03 to 0.34 m under SSP5-8.5.''' The loss of ice from Greenland will become increasingly dominated by surface melt, as marine margins retreat and the ocean-forced dynamic response of ice-sheet margins diminishes ( ''high confidence'' ). In the Antarctic, dynamic losses driven by ocean warming and ice-shelf disintegration will ''likely'' continue to outpace increasing snowfall this century ( ''medium confidence'' ). Beyond 2100, total mass loss from both ice sheets will be greater under high-emissions scenarios than under low-emissions scenarios ( ''high confidence'' ). The assessed ''likely'' ranges consider those ice-sheet processes in whose representation in current models we have at least ''medium confidence'' , including surface mass balance and grounding-line retreat in the absence of instabilities. Under high-emissions scenarios, poorly understood processes related to marine ice sheet instability and marine ice cliff instability, characterized by deep uncertainty, have the potential to strongly increase Antarctic mass loss on century to multi-century time scales. {9.4.1, 9.4.2, 9.6.3, Box 9.3, Box 9.4}

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