Present and future mass balance of the ice sheets simulated with GCM

Abstract

A high-resolution GCM ECHAM3 T106 was used to simulate the climates of the present and of the future under doubled CO2 The ECHAM3 T106 was integrated for an equivalent time of 5 years (1) with the observed SST of the 1980s and (2) with the SST for the 2 × CO2 climate generated from the ECHAM1 T21 coupled transient experiment. The main motivation for using the GCM to simulate the mass balance is the level of skill in simulating precipitation and accumulation recently achieved in the high-resolution GCM experiment. The ablation is computed, based on the GCM internal surface fluxes and the temperature/ablation relationship formulated on the Greenland field data. The two ice sheets show very different reactions towards doubling the CO2. As the decrease in accumulation and the increase in ablation in Greenland cause an annual mean specific mass balance of −225 mm (eq. −390 km3), the increase in accumulation and virtually non-melt conditions in Antarctica result in a mean annual specific mass balance of + 23 mm (eq. + 325 km3). The sum of the mass balance on both ice sheets is equivalent to the annual sea-level rise of 0.2 mm. This experiment shows that other mechanisms for sea-level change, such as the thermal expansion of the sea water and the melt of small mountain glaciers, will remain important in the coming century.