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 %).