| Abstract: | As a guide to the possible effects of a CO2-induced warming on the cryosphere, we review the effects of three warm periods in the past, and out theoretical understanding of fluctuations in mountain glaciers, the Greenland and Antarctic ice sheets, ground ice, sea ice and seasonal snow cover. Between 1890 and 1940 A.D. the glaciated area in Switzerland was reduced by over 25%. In the Hypsithermal, at about 6000 BP, ground ice in Eurasia retreated northward by several hundred kilometres. In the interglacial Stage 5e, at about 120 000 BP, global sea-level rose by over 6 m. Fluctuations of mountain glaciers depend on mesoscale “weather” and on their mechanical response to it. Any melting of the Greenland ice sheet is likely to be slow in human terms. The West Antarctic ice sheet (its base below sea-level) is susceptible to an ungrounding, and such an event may have been the cause of the sea-level rise above. The East Antarctic ice sheet is susceptible to mechanical “surges”, which might be triggered by a warming at its margin. Both an ungrounding and a surge might occupy less than 100 yr, and are potetially the most important ice changes in human terms. Modelling studies suggest that a 5°C warming would remove the Arctic pack ice in summer, and this may be the most significant effect for further climatic change. |
