ALBERT

Description: Sea level rise associated with changing climate is expected to pose a major challenge for societies. Here, we estimate the future contribution of the Greenland ice sheet (GrIS) to sea level change in terms of different ice sheet atmospheric forcings arising from three general circulation models (GCMs), HadGEM2-ES, IPSL-CM5A-LR and MIROC5, for RCP2.6. We run the ice sheet model ISSM with higher order approximation and use a spin-up/inversion scheme to estimate the present day state. The forcing fields for surface mass balance (SMB) and ice surface temperature Ts are computed by the SEMIC model (Krapp et al., 2017) and applied as anomalies to RACMO2.3 fields. According to the three GCMs, warming of 1.5 °C has been reached at GrIS by 2005 (HadGEM2-ES, MIROC5) or as early as 1995 (IPSL-CM5A-LR). Forcing fields suffer from underestimation of polar amplification (MIROC5) and implausible distribution of changes in Ts (IPSL-CM5A-LR). HadGEM2-ES is the most plausible forcing, with globally a peak and decline behaviour leading to overshooting of 1.5 °C and over GrIS a slight recovery of SMB towards values of about half the present day SMB. We find sea level to rise for HadGEM2-ES by 71 mm by 2100 and 189 mm by 2300. Simulated an observed sea level rise 2002–2014 is of the same magnitude, but with a temporal lag to be at least five years (HadGEM2-ES). By end of 22nd century sea level contribution is still 0.46 mm/a for HadGEM2-ES. Hence, even a RCP2.6 peak and decline scenario will lead to significant changes of GrIS including elevation changes up to 100 m and loss of floating tongues. The values of this study may serve as a lower bound, as processes proven to play a major role in GrIS mass loss are not yet represented by the model, but are considerably larger than other studies.