Relative importance of surface mass balance and outlet glacier forcing in ISMIP6 Greenland ice sheet sea-level projections

The Greenland ice sheet (GrIS) is one of the largest contributors to global mean sea-level rise today and is expected to continue losing mass in the future under increasing Arctic warming. Mass loss in the future is caused by the thinning and retreat of marine-terminating outlet glaciers and to a larger extent by decreasing surface mass balance (SMB) due to increased surface meltwater runoff. In this paper we study the relative importance of changes in SMB and outlet glacier retreat by means of model simulations that have been performed as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). The effect of the two forcing mechanisms can be separated based on a comparison between full projections and single forcing experiments up to year 2100 for a number of ice sheet models, driving General Circulation Models and two forcing scenarios (RCP2.6 and RCP8.5). We can confirm earlier findings for the high forcing scenario that a compensation between the two processes renders the sea-level contribution from the full experiment lower than the sum of the single forcing experiments.