Mass balance of the ice sheets of Antarctica and Greenland and their changes: The freshwater resources of the two ice sheets in Antarctica and Greenland represent a potential rise of the global sea level of 70 m. So far it was assumed that for a moderate rise in global temperature the enhanced ice melt in Greenland will be compensated by higher accumulation rates in the interior of Antarctica. Only a further increase in temperatures will lead to a noti- ceable contribution to sea level from the polar ice sheet. A number of recent investigations demonstrate that the sen- sitivity of the ice sheets to temperature changes is much higher. Not only higher melt rates, but also ice dynamic ef- fects will lead to the disappearance of the Greenland Ice Sheet if temperatures rise a further three degrees. But also in Antarctica some areas, especially the West Antarctic Ice Sheet and the glaciers of the Antarctic Peninsula, alrea- dy react very sensitive on the ongoing climatic change which leads to a positive contribution to global sea level.