Ice loss in High Mountain Asia and the Gulf of Alaska observed byCryoSat-2 swath altimetry between 2010 and 2019

Abstract. Glaciers and ice caps are currently the largest non-steric contributor to sea level rise, contributing ~30 % to sea level budget. Global monitoring of these regions remains a challenging task since global estimates rely on a variety of observations and models to achieve the required spatial and temporal coverage, and significant differences remain between current estimates. Here we report the first application of a novel approach to retrieve spatially-resolved elevation and mass change from Radar Altimetry over entire mountain glaciers areas. We apply interferometric swath altimetry to CryoSat-2 data acquired between 2010 and 2019 over High Mountain Asia (HMA) and in the Gulf of Alaska (GoA). In addition, we extract monthly time series of elevation change, exploiting CryoSat's high temporal repeat, to reveal seasonal and multiannual variation in rates of glaciers' thinning at unprecedented spatial detail. We find that during this period, HMA and GoA have lost an average of −27.9 ± 2.4 Gt yr−1 (−0.29 ± 0.03 m w.e. yr−1) and −76.3 ± 5.6 Gt yr−1 (−0.89 ± 0.07 m w.e. yr−1) respectively, corresponding to a contribution to sea level rise of 0.048 ± 0.004 mm yr−1 and 0.217 ± 0.015 mm yr−1. Glacier thinning is ubiquitous except for the Karakoram-Kunlun region experiencing stable or slightly positive mass balance. In the GoA region the intensity of thinning varies spatially and temporally and correlates with the strength of the Pacific Decadal Oscillation. In HMA we observe sustained multiannual trends until 2015-6, and decreased loss or even mass gain from 2016-17 onwards.