Editing IPCC:AR6/WGI/Chapter-8 (section)

===== 8.3.1.7.1 Glaciers =====

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The AR5 and SROCC found, with ''very high confidence,'' a general decline in glaciers due to climate change in recent decades. There is ''very high confidence'' that during the decade 2010–2019 glaciers lost more mass than in any other decade since the beginning of the observational record (Sections 2.3.2.3 and 9.5.1). Human influence is ''very likely'' the main driver of the global, near-universal retreat of glaciers since the 1990s ( [[IPCC:Wg1:Chapter:Chapter-3#3.4.3.1|Section 3.4.3.1]] ). In Table 9.5, the contribution of glaciers to sea level rise for different periods is presented; in 1971 – 2018 glacier mass loss contributed 20.9 [10.0 to 31.7] mm or 22.2% of the sea level rise during that period. The highest mass loss rates are observed in the southern Andes, New Zealand, Alaska, Central Europe and Iceland while the largest mass loss are observed in Alaska, the periphery of Greenland and Arctic Canada ( [[IPCC:Wg1:Chapter:Chapter-9#9.5.1%20|Section 9.5.1]] and Figure 9.20). Predominantly '','' runoff from small glaciers such as in Canada has decreased because of glacier mass loss, while runoff from larger glaciers such as in Alaska has typically increased ( [[#Bolch--2010|Bolch et al., 2010]] ; [[#Thomson--2011|Thomson et al., 2011]] ; [[#Tennant--2012|Tennant et al., 2012]] ; [[#WGMS--2017|WGMS, 2017]] ; [[#Huss--2018|Huss and Hock, 2018]] ). Asia contains the largest concentration of glaciers outside the polar regions where the total glacier mass change is –16.3 ± 3.5 Gt yr <sup>–1</sup> over 2000 – 2016 with considerable intra-regional variability ( [[#Brun--2017|Brun et al., 2017]] ). Mass losses of glaciers in Asia between 2000 and 2018 are – 19.0 ± 2.5 Gt yr <sup>–1</sup> ( [[#Shean--2020|Shean et al., 2020]] ). The most negative changes were found in Nyainqentanglha with −4.0 ± 1.5 Gt yr <sup>–1</sup> , while glaciers in Kunlun, northern Tibetan Plateau, slightly gained mass at 1.4 ± 0.8 Gt yr <sup>–1</sup> .

There is some evidence that an increase of precipitation over high mountains can offset glacier ablation (melt; [[#Farinotti--2020|Farinotti et al., 2020]] ). However, this process has only been described from the Karakoram region in the north-western Himalaya, where it is thought to be partly responsible to the advances of glacier changes in the last two decades, referred to as the ‘Karakoram Anomaly’ ( [[#Farinotti--2020|Farinotti et al., 2020]] ). In the Himalaya, [[#Maurer--2019|Maurer et al. (2019)]] observed faster ice loss during 2000–2016 (7.5 ± 2.3 Gt yr <sup>–1</sup> ) compared to 1975–2000 (–3.9 ± 2.2 Gt yr <sup>–1</sup> ). In the Southern Hemisphere, the rate of glacier mass lost in South America is estimated at 19.4 ± 0.6 Gt yr <sup>–1</sup> based on surface elevation changes over 2000 – 2011, which include the North and South Patagonian Icefields of South America ( [[#Braun--2019|Braun et al., 2019]] ), and at −22.9 ± 5.9 Gt yr <sup>–1</sup> over 2000 – 2018 ( [[#Dussaillant--2019|Dussaillant et al., 2019]] ).

In summary, human-induced global warming has been the primary driver of a global glacier recession since the early 20th century ( ''high confidence'' ). Most glaciers have lost mass more rapidly since the 1960s and in an unprecedented way over the last decade, thereby contributing to increased glacier runoff, especially from larger glaciers until a maximum is reached, which tends to occur later in basins with larger glaciers and higher ice-cover fractions ( ''high co'' ''nfidence'' ).

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