On the response of the Greenland ice sheet to greenhouse climate change

Numerical computations are performed with the three-dimensional polythermal ice-sheet model SICOPOLIS in order to investigate the possible impact of a greenhouse-gas-induced climate change on the Greenland ice sheet. The assu med increase of the mean annual air temperature above the ice covers a rang e from Delta T = 1 degrees C to 12 degrees C, and several parameterizations for the snowfall and the surface melting are considered. The simulated shr inking of the ice sheet is a smooth function of the temperature rise, indic ations for the existence of critical thresholds of the climate input are no t found. Within 1000 model years, the ice-volume decrease is limited to 10% of the present volume for Delta T less than or equal to 3 degrees C, where as the most extreme scenario, Delta T = 12 degrees C, leads to an almost en tire disintegration, which corresponds to a sea-level equivalent of 7 m. Th e different snowfall and melting parameterizations yield an uncertainty ran ge of up to 20% of the present ice volume after 1000 model years.