The future of Upernavik Isstrøm through the ISMIP6 framework: sensitivity analysis and Bayesian calibration of ensemble prediction

Abstract. This study investigates the uncertain future contribution to sea-level rise in response to global warming of Upernavik Isstrøm, a tidewater glacier in Greenland. We analyse multiple sources of uncertainty, including Shared Socioeconomic Pathways (SSPs), climate models (global and regional), ice–ocean interactions, and ice sheet model (ISM) parameters. We use weighting methods based on spatio-temporal velocity and elevation data to reduce ice flow model uncertainty and evaluate their ability to prevent overconfidence. Our developed initialization method demonstrates the capability of Elmer/Ice to accurately replicate the hindcast mass loss of Upernavik Isstrøm. Future mass loss predictions in 2100 range from a contribution to sea-level rise from 1.5 to 7.2 mm, with an already committed sea-level contribution projection from 0.6 to 1.3 mm. At the end of the century, SSP-related uncertainty constitutes the predominant component of total uncertainty, accounting for 40 %, while uncertainty linked to the ISM represents 15 % of the overall uncertainty. We find that calibration does not reduce uncertainty in the future mass loss between today and 2100 (+2 %) but significantly reduces uncertainty in the hindcast mass loss between 1985 and 2015 (−32 % to −61 % depending on the weighting method). Combining calibration of the ice sheet model with SSP weighting yields uncertainty reductions in future mass loss in 2050 (−1.5 %) and in 2100 (−32 %).