Description: The Greenland ice sheet is modelled to simulate its extent and volume in warmer climates, and also to find out whether the ice sheet would re-form on theice-free bedrock under present climatic conditions. The ice sheet model is a three-dimensional thermo-mechanical model with a fine resolution grid. Thebedrock surface beneath the ice sheet was mapped using radio-echo-sounding measurements by the Electromagnetic Institute, Copenhagen. The modelexperiments show that increased temperature will result in ice-margin retreat, but the ice sheet is relatively stable; it takes a rather high temperature rise of atleast 6¡C for the ice sheet to disappear completely, which indicates that the ice sheet probably survived the last interglacial. Also, it appears that the Greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re-form on the bare bedrock under the present, or evenslightly warmer, climatic conditions.

Description: Increased melting on glaciers and ice sheets and rising sea level are often mentioned as important aspects of the anticipated greenhouse warming of the earth'satmosphere. This paper deals with the sensitivity of Greenland's ice mass budget and presents a tentative projection of the Greenland component of future sealevel rise for the next few hundred years. To do this, the 'Villach II temperature scenario' is prescribed, and output from a comprehensive mass balancemodel is used to drive a high-resolution 3-D thermomechanic model of the ice sheet.The mass balance model consists of two parts: the accumulation part is based on presently observed values and is forced by changes in mean annual airtemperature. The ablation model is based on the degree-day method and accounts for the daily and annual temperature cycle, a different degree-day factor forice and snow melting and superimposed ice formation. Under present-day climatic conditions, the following total mass balance results (in ice equivalent peryear): 599.3 109 m3 of accumulation, 281.7 109 m3 of runoff and assuming a balanced budget, 317.6 109 m3 of iceberg calving. A 1K uniform warming isthen calculated to increase the runoff by 119.5 109 m3. Since accumulation also increases by 32 109 m3, this leads to reduction of the total mass balance by87.5 109 m3 of ice, corresponding to a sea level rise of 0.22 mm/year. For a temperature increase larger than 2.7 K, runoff exceeds accumulation, and if icesheet dynamics were to remain unchanged, this would add an extra amount of 0.8 mm/year to the worlds' oceans.Imposing the Villach II scenario (warming up to 4.2 K) and accumulating mass balance changes forward in time (static response) would then result in aglobal sea level rise of 7.1 cm by 2100 AD, but this figure may go up to as much as 40 cm per century in case the warming is doubled. In a subsequentdynamic model run involving the ice flow, the ice sheet is found to produce a counteracting effect by dynamically producing steeper slopes at the margin,thereby reducing the area over which runoff can take place. This effect is particularly apparent in the northeastern part of the ice sheet, and is also morepronounced for the smaller temperature perturbations. Nevertheless, all these experiments certainly highlight the vulnerability of the Greenland ice sheet withrespect to a climatic warming.

Description: The evolution of the Greenland ice sheet during the last 150,000 years, in response to a climate history derived from a Greenland ice-margin oxygen-18 record,is simulated by means of a three-dimensional, time-dependent ice-sheet model. The calculations indicate that the ice sheet displayed considerable thinning andice-margin retreat during the last interglacial (the Eemian) and during a warm interstadial c. 100,000 yr B.P., resulting in splitting up of the ice sheet into acentral-northern and a southern part. However, the ice sheet in Central Greenland survived the warm stages with almost unchanged surface elevations ascompared with the present.