Extended Data Fig. 1: Svalbard’s estimated contribution to sea level rise: past and future.

The x-axis represents the total ice loss, expressed in terms of mm of global sea level equivalent (SLE). The SLE is normalized to a 100-yr period to facilitate comparison between historical observations of varying length and projections for the 21st century. For the historical models that only simulate climatic mass balance¹⁹, we added a calving flux⁸⁶ of −6.75 ± 1.7 Gt yr⁻¹ to estimate the total mass balance and facilitate comparison with the geodetic and gravimetric observations. Since the data are compiled from many sources^2,3,4,–⁵, ^{12,13,14,15,16,}–¹⁷, ⁸⁵, ^{87,88,89,90,91,92,93,94,95,96,97,}–⁹⁸, ¹⁰³, the error bars represent different quantities. In most cases, the shaded bars represent the reported ± 1σ uncertainty. For Marzeion et al. (2012), the bars represent the range of results from different ensemble runs, and for ‘This study’, the bars represent the range from using the 5th to 95th percentile of future precipitation estimates (Fig. 4). The 21st century projections for this study are broken into 3 groups: (1) those based on the 1936-2010 mass balance observations using mean summer temperature as the explanatory variable for ice loss (†; Figs. 3–4), (2) those based on the 2000-2019 satellite era observations⁴ using mean summer temperature (∗; Extended Data Fig. 10), and (3) those based on the 1936-2010 observations using positive degree days (‡; Extended Data Fig. 9). All three methods produce similar estimates for 21st century ice loss. The predictions begin to diverge under the most extreme warming scenario (RCP8.5)⁶, with the space-for-time substitution based on the positive degree day (PDD) approach (Extended Data Fig. 9) producing the highest estimates of sea level rise. Note that the total ice volume of Svalbard is estimated⁵⁹ to be ∼6,199 km³ which is equivalent to 15 mm of sea level rise. Thus, the 21st century predictions exceeding 15 mm of SLE^87,88,89 are not feasible.