Extended Data Fig. 8: Visual and quantitative comparison of the regional T_s vs. ∆h/∆t behavior of Svalbard glaciers.

(a-b) A visual comparison between glaciers in (a) NE Spitsbergen and (b) Edgeøya near the end of the 2020 melt season. Note that, in contrast to the glaciers in (a), the glaciers in (b) have no remaining winter snow, as evinced by the darker, debris-rich ice exposed even at the highest reaches of the glaciers. In other words, 100% of the glacier surface lies within the ablation zone. The Sentinel-2 imagery is from August 01, 2020 and the coordinates are in UTM zone 33N. (c-d) Glacier extents in 1936 and 2010. (e-i) Searching for evidence of threshold behavior in the Svalbard-wide 1936-2010 dataset. (e-f) If a strong tipping point already had been reached, such that, at high T_s, glaciers diverged from the linear behavior in Fig. 3, one might expect a T_s vs. ∆h/∆t relationship like that depicted in (f). However, (e) does not show strong support for the model in (f). Next, we look for a regional signal in the T_s vs. ∆h/∆t relationship. We divide the Svalbard-wide dataset into the 8 regions shown in (h), each of which has a different average T_s (g) and ∆h/∆t. (i) For each region, we study the residual between the Svalbard-wide linear T_s vs. ∆h/∆t (e) and the regional observations. The residuals are computed as predicted minus observed, so negative values indicate that the observed mass balance is more negative than the predictions. The regions in (i) are ordered according to the region-averaged glacier bed slope (Extended Data Fig. 7c), from smallest to largest. The glaciers like those in (b) that are committed to a path of pure melting (no accumulation) appear to follow similar T_s vs. ∆h/∆t relationships as the healthier (close to balance) glaciers in (a).