MODELING THE SHORT-TERM RESPONSE OF THE GREENLAND ICE-SHEET TO GLOBALWARMING

A two-dimensional vertically integrated ice flow model has been develo ped to test the importance of various processes and concepts used for the prediction of the contribution of the Greenland ice-sheet to sea-l evel rise over the next 350 y (short-term response). The mass balance is modelled by the degree-day method and the energy-balance method. Th e lithosphere is considered to respond isostatically to a point load a nd the time evolution of the bedrock follows from a viscous asthenosph ere. According to the IPCC-IS92a scenario (with constant aerosols afte r 1990) the Greenland ice-sheet is likely to cause a global sea level rise of 10.4 cm by 2100 AD. It is shown, however, that the result is s ensitive to precise model formulations and that simplifications as use d in the sea-level projection in the IPCC-96 report yield less accurat e results. Our model results indicate that, On a time scale of a hundr ed years, including the dynamic response of the ice-sheet yields more mass loss than the fixed response in which changes in geometry are not incorporated. It appears to be important to consider sliding, as well as the fact that climate sensitivity increases for larger perturbatio ns. Variations in predicted sea-level change on a time scale of hundre d years depend mostly on the initial state of the ice-sheet. On a time scale of a few hundred years, however, the variability in the predict ed melt is dominated by the variability in the climate scenarios.