Abstract. The Greenland ice sheet is one of the largest contributors to global mean
sea-level rise today and is expected to continue to lose mass as the Arctic
continues to warm. The two predominant mass loss mechanisms are increased
surface meltwater run-off and mass loss associated with the retreat of
marine-terminating outlet glaciers. In this paper we use a large ensemble of
Greenland ice sheet models forced by output from a representative subset of
the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise
contributions over the 21st century. The simulations are part of the
Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the
sea-level contribution together with uncertainties due to future climate
forcing, ice sheet model formulations and ocean forcing for the two
greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results
indicate that the Greenland ice sheet will continue to lose mass in both
scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest
mass loss is expected from the south-west of Greenland, which is governed by
surface mass balance changes, continuing what is already observed today.
Because the contributions are calculated against an unforced control
experiment, these numbers do not include any committed mass loss, i.e. mass
loss that would occur over the coming century if the climate forcing
remained constant. Under RCP8.5 forcing, ice sheet model uncertainty
explains an ensemble spread of 40 mm, while climate model uncertainty and
ocean forcing uncertainty account for a spread of 36 and 19 mm,
respectively. Apart from those formally derived uncertainty ranges, the
largest gap in our knowledge is about the physical understanding and
implementation of the calving process, i.e. the interaction of the ice sheet
with the ocean.