Greenland Ice Sheet Contribution to 21st Century Sea Level Rise as Simulated by the Coupled CESM2.1‐CISM2.1

The Greenland Ice Sheet (GrIS) mass balance is examined with an Earth system/ice sheet model that interactively couples the GrIS to the broader Earth system. The simulation runs from 1850 to 2100, with historical and SSP5‐8.5 forcing. By the mid‐21st century, the cumulative GrIS contribution to global mean sea level rise (SLR) is 23 mm. During the second half of the 21st century, the surface mass balance becomes negative in all drainage basins, with an additional SLR contribution of 86 mm. The annual mean GrIS mass loss in the last two decades is 2.7‐mm sea level equivalent (SLE) year−1. The increased SLR contribution from the surface mass balance (3.1 mm SLE year−1) is partly offset by reduced ice discharge from thinning and retreat of outlet glaciers. The southern GrIS drainage basins contribute 73% of the mass loss in mid‐century but 55% by 2100, as surface runoff increases in the northern basins. Plain Language Summary The Greenland Ice Sheet (GrIS) gains mass at the surface from snowfall, and it loses mass from melting and runoff and from glacier calving at the ocean front. When these processes are in balance, the ice sheet does not contribute to global sea level change. Recent observations have shown that the ice sheet is losing mass and raising global mean sea level. This study uses a global Earth system model that calculates ice flow of the GrIS, as well as processes in the atmosphere, ocean, land, and sea ice. For a modern reference, the model is forced with atmospheric greenhouse gas concentrations for the period 1850–2014. Next, the model is forced for the rest of the 21st century following the SSP5‐8.5 scenario to study how the GrIS and the Earth system respond to a worst‐case scenario. By 2050, the GrIS loses mass that is equal to 23 mm of global mean sea level rise. During the second half of the 21st century, all regions of the GrIS lose mass because of increased surface melting and runoff, with the dry north playing a greater role. By 2100, the projected GrIS contribution to sea level rise is 109‐mm sea level equivalent. Key Points CESM2.1‐CISM2.1 simulates a 5.4 K global mean temperature increase and strong NAMOC weakening by 2100 in SSP5‐8.5 w.r.t. preindustrial The Greenland Ice Sheet contributes 23 mm to global mean sea level rise by 2050 and 109 mm by 2100 The role of the northern basins becomes more important as surface runoff strongly increases during the second half of the 21st century