What is the current mass balance of ice sheets and glaciers?
Ice-sheet or glacier mass balance is defined as the annual difference between mass gain and mass loss. It is important globally because it has a dominant effect on sea-level change. During the last glacial maximum, global sea level was approximately 125 meters lower, the water being locked up primarily in the now-extinct Laurentide and Fennoscandian ice sheets of the Northern Hemisphere and an expanded Antarctic ice sheet (Shackleton, 1987; Denton and Hughes, 1981). Present ice volume, which is contained mostly in the Antarctic and Greenland ice sheets, is sufficient to raise sea level approximately 80 meters (Bader, 1961, Drewry et al., 1982). By comparison, the annual turnover in ice-sheet mass is modest. Annual snow accumulation over the Antarctic and Greenland ice sheets is equivalent to an ocean layer only 6 mm thick (Bentley and Giovenetto, 1991; Ohmura and Reeh, 1991). A nearly equivalent amount of ice is returned to the oceans through melting and iceberg discharge. Estimates of
