Editing IPCC:AR6/WGI/Chapter-1 (section)

===== ''1.5.1.1.3 Cryosphere'' =====

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For the cryosphere, there has been much recent progress in synthesizing global datasets covering larger areas and longer time periods from multi-platform observations. For glaciers, the Global Terrestrial Network for Glaciers, which combines data on glacier fluctuations, mass balance and elevation change with glacier outlines and ice thickness, has expanded and provided input for assessing global glacier evolution and its role in sea level rise (Sections 2.3.2.3 and 9.5.1; [[#Zemp--2019|Zemp et al., 2019]] ). New data sources include archived and declassified aerial photographs and satellite missions, and high-resolution (10 m or less) digital elevation models ( [[#Porter--2018|Porter et al., 2018]] ; [[#Braun--2019|Braun et al., 2019]] ).

Improvements have also been made in the monitoring of permafrost. The Global Terrestrial Network for Permafrost (GTN-P; [[#Biskaborn--2015|Biskaborn et al., 2015]] ) provides long-term records of permafrost temperature and active layer thickness at key sites to assess their changes over time. Substantial improvements to our assessments of large-scale snow changes come from intercomparison and blending of several datasets, for snow water equivalent ( [[#Mortimer--2020|Mortimer et al., 2020]] ) and snow cover extent ( [[#Mudryk--2020|Mudryk et al., 2020]] ), and from bias corrections of combined datasets using in situ data (Sections 2.3.2.5 and 9.5.2; [[#Pulliainen--2020|Pulliainen et al., 2020]] ).

The value of gravity-based estimates of changes in ice-sheet mass has increased, as the time series from the GRACE and GRACE-FO satellites – homogenized and absolutely calibrated – is close to 20 years in length. The European Space Agency’s (ESA’s) Cryosat-2 radar altimetry satellite mission has continued to provide measurements of the changes in the thickness of sea ice and the elevation of the Greenland and Antarctic ice sheets ( [[#Tilling--2018|Tilling et al., 2018]] ). Other missions include NASA’s Operation IceBridge, collecting airborne remote-sensing measurements to bridge the gap between ICESat (Ice, Cloud and land Elevation Satellite) and the upcoming ICESat-2 laser altimetry missions. Longer time series from multiple missions have led to considerable advances in understanding the origin of inconsistencies between the mass balances of different glaciers and reducing uncertainties in estimates of changes in the Greenland and Antarctic ice sheets ( [[#Bamber--2018|Bamber et al., 2018]] ; [[#Shepherd--2018|A. Shepherd et al., 2018]] ; [[#Shepherd--2020|Shepherd et al., 2020]] ). Last, the first observed climatology of snowfall over Antarctica was obtained using the cloud/precipitation radar onboard NASA’s CloudSat ( [[#Palerme--2014|Palerme et al., 2014]] ).

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