Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.4.4 Snow and Ice ====

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'''Snow:''' Historical studies of seasonal snow cover are limited and restricted to the Andes Cordillera. [[#Mernild--2017|Mernild et al. (2017)]] indicated that much of the area north of 23°S experienced a decrease in the number of snow cover days, while the southern half of the Andes Cordillera experienced the opposite. A reduction in snow cover of about 15% was simulated for areas with altitudes in the range of 3000–5000 m, whereas in regions with altitude below 1000 m (Patagonia) snow cover extent increased. The reduced snowfall over the Chilean and Argentinean Andes mountains, which has resulted in unprecedented reductions in river flow, reservoir volumes and groundwater levels, led to the most severe and long-lasting hydrological drought (2010–2015) reported in the adjacent semi-arid foothills of the central Andes ( [[#Garreaud--2017|Garreaud et al., 2017]] ; [[#Rivera--2017|Rivera et al., 2017]] ; [[#Masiokas--2020|Masiokas et al., 2020]] ). Projections (based on process understanding) in [[IPCC:Wg1:Chapter:Chapter-9#9.5.3.3|Section 9.5.3.3]] point to decreases in seasonal snow cover extent and duration across South America as global climate continues to warm ( ''high confidence'' ).

'''Glacier:''' Observation and future projection of Central and South America glacier mass changes are assessed in [[IPCC:Wg1:Chapter:Chapter-9#9.5.1|Section 9.5.1]] , grouped in two main regions: Low Latitude region (98% of which is glaciers in the Andes) and the Southern Andes region. An increase in the number and areal extent of glacial lakes in the Southern Andes was reported for the period 1986–2016 ( [[#Wilson--2018|Wilson et al., 2018]] ). Similar changes are being observed in the central Andes ( [[#Colonia--2017|Colonia et al., 2017]] ). Since 1800 at least 15 ice‐dammed lakes and 16 moraine‐dammed lakes have failed in the extratropical Andes, causing high-magnitude glacial lake outburst floods ( [[#Rojas--2014|Rojas et al., 2014]] ; [[#Cook--2016|Cook et al., 2016]] ; [[#Wilson--2018|Wilson et al., 2018]] ; [[#Drenkhan--2019|Drenkhan et al., 2019]] ). Partially due to glacier shrinkage and lake growth, the frequency of outburst floods has increased in the last 30–40 years ( [[#Carey--2012|Carey et al., 2012]] ; [[#Iribarren%20Anacona--2015|Iribarren Anacona et al., 2015]] ).

Glaciers across South America are expected to continue to lose mass and glacier area in the coming century ( ''high confidence'' ) ( [[IPCC:Wg1:Chapter:Chapter-9#9.5|Section 9.5]] ). In terms of their mass, glaciers in the Low Latitude region are projected by GlacierMIP to lose 67 ± 42%, 86 ± 24% and 94 ± 13%, of their 2015 baseline mass by the end of the century under RCP2.6, RCP4.5 and RCP8.5 respectively ( [[#Marzeion--2020|Marzeion et al., 2020]] ). Glaciers in the Southern Andes show decreasing mass loss rates for RCP2.6, and increasing rates for RCP8.5, which peak in the mid to late 21st century. Glaciers in the Southern Andes are projected to lose 26 ± 27%, 33 ± 26% and 47 ± 26% of their 2015 mass by the end of the century under RCP2.6, RCP4.5 and RCP8.5 respectively ( [[IPCC:Wg1:Chapter:Chapter-9#9.5.1.3|Section 9.5.1.3]] ).

The central Andes will experience the highest disturbance to the thermal regime of the 21st century. As a consequence, in the Argentinean Andes up to 95% of rock glaciers in the southern desert Andes and in the central Andes will rest in areas above 0°C under the worst case scenario of warming (the freezing level might move up more than twice as much as during the entire Holocene; [[#Drewes--2018|Drewes et al., 2018]] )

'''Permafrost:''' There is limited information on the ongoing changes and projections of permafrost conditions in the region. Based on model projections under the IPCC A1B scenario, permafrost areas in the Bolivian Andes will eventually be lost, but this could take years to decades or longer depending on permafrost thickness ( [[#Rangecroft--2016|Rangecroft et al., 2016]] ).

'''In conclusion, glacier volume loss and permafrost thawing will continue in the Andes Cordillera under all climate scenarios''' ( ''high confidence'' '''), causing important reductions in river flow and potentially high-magnitude glacial lake outburst floods.'''

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