A Factor Two Difference in 21st-Century Greenland Ice Sheet Surface Mass Balance Projections from Three Regional Climate Models for a Strong Warming Scenario (SSP5-8.5)

The Arctic is warming rapidly, significantly reducing the Greenland ice sheet (GrIS) surface mass balance (SMB) and raising its contribution to global sea-level rise. Since these trends are expected to continue, it is essential to explore the GrIS SMB response to projected climate warming. We compare projections from three polar regional climate models, RACMO, MAR, and HIRHAM, forced by the Community Earth System Model CESM2 under a high-end warming scenario (SSP5-8.5, 1970-2099). We reveal different modeled SMB by 2100, including a twofold larger annual surface mass loss in MAR (-1735 Gt/yr) and HIRHAM (-1698 Gt/yr) relative to RACMO (-964 Gt/yr). Discrepancies primarily stem from differences in projected runoff, triggering melt-albedo positive feedback and subsequent modelled ablation zone expansion. In addition, we find different responses of modeled meltwater production to similar atmospheric warming. Our analysis suggests clear avenues for model developments to further improve SMB projections and contribution to sea-level rise.