The Greenland Ice Sheet is a vast body of ice covering 1.71 million km², roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost 2,400 kilometers long in a north-south direction, and its greatest width is 1,100 kilometers at a latitude of 77° N, near its northern margin. The mean altitude of the ice is 2,135 meters. The thickness is generally more than 2 km (see picture) and over 3 km at its thickest point. It is not the only ice mass of Greenland - isolated glaciers and small ice caps cover between 76,000 and 100,000 square kilometers around the periphery. Some scientists believe that global warming may be about to push the ice sheet over a threshold where the entire ice sheet will melt in less than a few hundred years. If the entire 2.85 million km³ of ice were to melt, it would lead to a global sea level rise of 7.2 m (23.6 ft.) Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) [Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp. tar/wg1/412.htm#tab113" target="_blank">http://www.grida.no/climate/ipcc_tar/wg1/412.htm#tab113,http://www.grida.no/climate/ipcc_tar/wg1/418.htm, and http://www.grida.no/climate/ipcc_tar/wg1/432.htm#fig1116. . This would inundate most coastal cities in the world and remove several small island countries from the face of Earth, since island nations such as _Tuvalu and Maldives have a maximum altitude below or just above this number.
The Greenland Ice Sheet is also sometimes referred to under the term inland ice, or its Danish equivalent, indlandsis. It is also sometimes referred to as an ice cap. Ice sheet, however, is considered the more correct term as ice cap generally refers to less extensive ice masses.
The ice in the current ice sheet is as old as 110,000 years However, it is generally thought that the Greenland Ice Sheet formed in the late Pliocene or early Pleistocene by coalescence of ice caps and glaciers. It did not develop at all until the late Pliocene, but apparently developed very rapidly with the first continental glaciation.
The massive weight of the ice has depressed the central area of Greenland; the bedrock surface is near sea level over most of the interior of Greenland, but mountains occur around the periphery, confining the sheet along its margins. If the ice were to disappear, Greenland would most probably appear as an archipelago. The ice surface reaches its greatest altitude on two north-south elongated domes, or ridges. The southern dome reaches almost 3,000 metres at latitudes 63° - 65° N; the northern dome reaches about 3,290 metres at about latitude 72° N. The crests of both domes are displaced east of the centre line of Greenland. The unconfined ice sheet does not reach the sea along a broad front anywhere in Greenland, so that no large ice shelves occur. The ice margin just reaches the sea, however, in a region of irregular topography in the area of Melville Bay southeast of Thule. Large outlet glaciers, which are restricted tongues of the ice sheet, move through bordering valleys around the periphery of Greenland to calve off into the ocean, producing the numerous icebergs that sometimes occur in North Atlantic shipping lanes. The best known of these outlet glaciers is the Jakobshavn Isbræ, which, at its terminus, flows at speeds of 20 to 22 metres per day.
On the ice sheet, temperatures are generally substantially lower than elsewhere in Greenland. The lowest mean annual temperatures, about -31°C (-24°F), occur on the north-central part of the north dome, and temperatures at the crest of the south dome are about -20°C (-4°F).
During winter the ice sheet takes on a strikingly clear blue/green color. During summer the top ice layer melts leaving pockets of air in the ice that makes the ice look all white.
