Changes of the polar ice sheets

An overview is given of the basic response mechanisms of the Greenland and Antarctic ice sheets to global warming. It is explained how surface mass-balance changes are likely to dominate the response, though it is stressed that important uncertainties remain concerning the present evolution of the ice sheets, the relation between climatic changes and the mass balance terms of snow accumulation and meltwater runoff, and the possible instability of the West Antarctic ice sheet. According to the mid-range of the IPCC (1996) climatic projections, melting would be most important on the Greenland ice sheet and contribute about 10 cm to global sea levels by the year 2100. The Antarctic ice sheet, on the other hand, would grow slightly, because increased precipitation rates would dominate over increased melting rates and dynamic effects in West Antarctica remain small. A likely estimate for the Antarctic contribution to global sea-level lowering is around 10 cm by the year 2100, which would largely balance the Greenland contribution.