Improved Understanding of Multicentury Greenland Ice Sheet Response to Strong Warming in the Coupled CESM2-CISM2 With Regional Grid Refinement

The simulation of ice sheet-climate interactions, such as surface mass balance fluxes, is sensitive to model grid resolution. Here we simulate the multi-century evolution of the Greenland Ice Sheet (GrIS) and its interaction with the climate using the Community Earth System Model version 2.2 (CESM2.2) including an interactive GrIS component (the Community Ice Sheet Model v2.1 [CISM2.1]) under an idealized warming scenario (atmospheric ${\text{CO}}_2$ increases by 1% ${\text{yr}}^{-1}$ until quadrupling the pre-industrial level and then is held fixed). A variable-resolution (VR) grid with 1/$4°$ regional refinement over the broader Arctic and $1°$ resolution elsewhere is applied to the atmosphere and land components, and the results are compared with conventional $1°$ lat-lon grid simulations to investigate the impact of grid refinement. Compared with the $1°$ runs, the VR run features a slower rate of surface melt, especially over the western and northern GrIS, where the ice surface slopes gently toward the periphery. This difference pattern originates primarily from higher snow albedo and, thus, weaker albedo feedback in the VR run. The VR grid better captures the CISM ice sheet topography by reducing elevation discrepancies between CAM and CISM and is, therefore, less reliant on the downscaling algorithm, which is known to underestimate albedo gradients. The sea level rise contribution from the GrIS in the VR run is 53 mm by year 150 and 831 mm by year 350, approximately 40% and 20% less than that of the $1°$ runs, respectively.