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Ice sheet
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Ice sheet

An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 square kilometers (12 million acres). The only current ice sheets are Antarctica and Greenland (Iceland? perhaps too small: probably an ice cap); formerly the Laurentide ice sheet covered much of Canada and North America.

Ice sheets are bigger than ice shelves or glaciers.

Although the surface is cold, the base of an ice sheet is generally warmer, in places it melts and the melt-water lubricates the ice sheet so that it flows more rapidly. This process produces fast-flowing channels in the ice sheet - these are ice streams.

The Antarctic ice sheet is the largest single mass of ice on Earth. It covers an area of almost 14 million km 2 and contains 30 million km 3 of ice. Around 90 per cent of the fresh water on the Earth's surface is held in the ice sheet, an amount equivalent to 70 m of water in the world's oceans. In East Antarctica the ice sheet rests on a major land mass, but in West Antarctica the bed is in places more than 2500 m below sea level. It would be seabed if the ice sheet were not there.

The Greenland ice sheet occupies about 82% of the surface of Greenland, and if melted would contribute approximately 5 m of sea level rise.

If global warming occurs, over the next century the Antarctic ice sheet is predicted to gain mass (primarily because it is so cold that the extra warmth will not melt it significantly but will supply extra moisture; conversely the Greenland ice sheet is expected to lose mass through melting. These effects are expected to approximately cancel [1].