Abstract
Abstract. Glaciers are currently the largest contributor to sea level rise after ocean thermal expansion, contributing ∼ 30 % to the 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 exploit CryoSat's monthly 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 −28.0 ± 3.0 Gt yr−1 (−0.29 ± 0.03 m w.e. yr−1) and −76.3 ± 5.7 Gt yr−1 (−0.89 ± 0.07 m w.e. yr−1), respectively, corresponding to a contribution to sea level rise of 0.078 ± 0.008 mm yr−1 (0.051 ± 0.006 mm yr−1 from exorheic basins) and 0.211 ± 0.016 mm yr−1. The cumulative loss during the 9-year period is equivalent to 4.2 % and 4.3 % of the ice volume, respectively, for HMA and GoA. Glacier thinning is ubiquitous except for in the Karakoram–Kunlun region, which experiences stable or slightly positive mass balance. In the GoA region, the intensity of thinning varies spatially and temporally, with acceleration of mass loss from −0.06 ± 0.33 to −1.1 ± 0.06 m yr−1 from 2013, which correlates with the strength of the Pacific Decadal Oscillation. In HMA ice loss is sustained until 2015–2016, with a slight decrease in mass loss from 2016, with some evidence of mass gain locally from 2016–2017 onwards.
Highlights
Glaciers store less than 1 % of the mass (Farinotti et al, 2019) and occupy just over 4 % of the area (RGI Consortium, 2017) of global land ice; their rapid rate of mass loss has accounted for almost a third of the global sea level rise during the 21st century (Gardner et al, 2013; WCRP Global Sea Level Budget Group, 2018; Wouters et al, 2019; Zemp et al, 2019), the largest sea level rise (SLR) contribution from land ice (Bamber et al, 2018; Slater et al, 2021)
Given that it is estimated that 40 % of High Mountain Asia (HMA) glaciers are not sampled due to onboard-tracking limitations (Dehecq et al, 2013) we estimate that with an appropriate onboard-tracking system, the rate coverage for HMA would be as high as 50 %
These values are within the high end of the range of observational methods (Zemp et al, 2019) whilst generally lower than the coverage provided by high-resolution sensors (Brun et al, 2017; Shean et al, 2020)
Summary
Glaciers store less than 1 % of the mass (Farinotti et al, 2019) and occupy just over 4 % of the area (RGI Consortium, 2017) of global land ice; their rapid rate of mass loss has accounted for almost a third of the global sea level rise during the 21st century (Gardner et al, 2013; WCRP Global Sea Level Budget Group, 2018; Wouters et al, 2019; Zemp et al, 2019), the largest sea level rise (SLR) contribution from land ice (Bamber et al, 2018; Slater et al, 2021). The quantification of mass loss in glaciers has posed scientific challenges, resulting in the need to combine various types of observation and the need to reconcile results obtained using different methods (Gardner et al, 2013). The traditional approach (glaciological method) extrapolates in situ observations (Bolch et al, 2012; Cogley, 2011; Yao et al, 2012; Zemp et al, 2019); measurements are sparse and possibly biased towards better accessible glaciers located at lower altitudes (Fujita and Nuimura, 2011; Gardner et al, 2013; Wagnon et al, 2013). Geodetic remote sensing methods rely on comparisons of topographic data or gravity fields to determine glacier changes. Recent geodetic remote sensing methods include (1) digital elevation model. Jakob et al.: Ice loss in High Mountain Asia and the Gulf of Alaska between 2010 and 2019
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