GREB-ISM v1.0: A coupled ice sheet model for the Globally Resolved Energy Balance model for global simulations on timescales of 100 kyr

We introduce a newly developed global ice sheet model coupled to the Globally Resolved Energy Balance (GREB) climate model for the simulation of global ice sheet evolution on timescales of 100 kyr or longer (GREB-ISM v1.0). Ice sheets and ice shelves are simulated on a global grid, fully interacting with the climate simulation of surface temperature, precipitation, albedo, land-sea mask, topography and sea level. Thus, it is a fully coupled atmosphere, ocean, land and ice sheet model. We test the model in ice sheet stand-alone and fully coupled simulations. The ice sheet model dynamics behave similarly to other hybrid SIA (shallow ice approximation) and SSA (shallow shelf approximation) models, but the West Antarctic Ice Sheet accumulates too much ice using present-day boundary conditions. The coupled model simulations produce global equilibrium ice sheet volumes and calving rates like those observed for present-day boundary conditions. We designed a series of idealized experiments driven by oscillating solar radiation forcing on periods of 20, 50 and 100 kyr in the Northern Hemisphere. These simulations show clear interactions between the climate system and ice sheets, resulting in slow buildup and fast decay of ice-covered areas and global ice volume. The results also show that Northern Hemisphere ice sheets respond more strongly to timescales longer than 100 kyr. The coupling to the atmosphere and sea level leads to climate interactions between the Northern and Southern Hemispheres. The model can run global simulations of 100 kyrd-1 on a desktop computer, allowing the simulation of the whole Quaternary period (2.6 Myr) within 1 month.