Estimating mass balance components of the Greenland ice sheet from a long-term GCM simulation

The results from long term (1950–1991) climate simulations with an atmospheric general circulation model forced by observed sea surface temperatures are analysed for the Greenland ice sheet. Both annual mean values and the seasonal cycle of key variables including temperature, precipitation, evaporation and snow depth are presented and compared with available observational data. The results indicate that many of the large scale climatic features can be simulated implying that, if all relevant statistics are saved, it is possible to obtain realistic estimates of the key terms which determine the net balance of the ice sheet. Where the available statistics permit, estimates are provided of these terms including an estimate of the effect that temperature might have on the overall mass balance. The relationship between temperature and changes in total stored water is investigated by considering seasonal changes to the simulated snow pack depth. These imply that the loss of total stored water increases by about 7 km3 per degree increase in temperature over the early part of summer. The results indicate that the accumulation rate may have decreased over the period 1950–1991 due to cooling of the surrounding oceans. The sensitivity to temperature over this time indicates that the accumulation rate increases/decreases by about 65 mm(we) per year per degree of warming/cooling. The results do not include estimates of total melt, but existing estimates suggest that the sensitivity to temperature is at least as great as that for accumulation. This implies that the overall mass balance may have increased over the period 1950–1991 but will decrease if warming occurs in the future.