Evaluation of the Greenland ice sheet surface mass balance simulated by a regional climate model forced by some selected IPCC AR5/CMIP5 AOGCMs over the current climate.

Abstract. As part of the ICE2SEA project, the regional climate model MAR was forced by the general circulation model ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) over 1980-2099 at a resolution of 25km. For the A1B scenario, MAR projects a highly negative (-500 GT/yr) SMB rate at the end of this century and a induced mass loss corresponding to a sea level rise of ~7 cm over 2000-2100. However, the comparison with MAR forced by the ERA-40 reanalysis over 1980-1999 shows that MAR forced by the 20C3M scenario is not able to represent reliably the current SMB due to biases in the general circulation and in the free atmosphere summer temperature modeled by ECHAM5 around the GrIS. These biases induce in MAR an underestimation of the snow accumulation and an overestimation of the surface melt. Therefore, this questions the reliability of these ECHAM5-forced future projections, knowing that i) these biases could be amplified in future and that ii) the MAR outputs are used to force ice sheets models for the ICE2SEA project. That is why, by waiting the outputs from the next generation of GCMs (CMIP5), we investigate the impacts of current climate biases over the future projections and we suggest corrections of ECHAM5 forcing files for having a better agreement with the ERA-40 forced simulation. This is useful for the ice sheet model wanting to use the absolute values of MAR future projections instead of anomalies.