It is the second largest ice body in the world, after the Antarctic ice sheet. The ice sheet is almost 2,900 kilometres long in a north–south direction, and its greatest width is 1,100 kilometres at a latitude of 77°N, near its northern margin. The mean altitude of the ice is 2,135 metres. The thickness is generally more than 2 km and over 3 km at its thickest point. In addition to the large ice sheet, smaller ice caps as well as glaciers, cover between 76,000 and 100,000 square kilometres around the periphery. If the entire 2,850,000 cubic kilometres of ice were to melt, it would lead to a global sea level rise of 7.2 m. The Greenland Ice Sheet is sometimes referred to under the term inland ice, or its Danish equivalent, indlandsis. It is also sometimes referred to as an ice cap.
The ice sheet, consisting of layers of compressed snow from more than 100,000 years, contains in its ice today's most valuable record of past climates. In the past decades, scientists have drilled ice cores up to 4 kilometres deep. Scientists have, using those ice cores, obtained information on temperature, ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity, desert extent and forest fires.
This variety of climatic proxies is greater than in any other natural recorder of climate, such as tree rings or sediment layers. This was not expected and may show Greenland to be more fragile and sensitive to climate change than previously thought. The melting ice sheet edit many scientists who study the ice ablation in Greenland consider that an increase in temperature of two or three degrees Celsius would result in a complete melting of Greenland's ice and leave Greenland completely submerged in water.
Positioned in the Arctic, the Greenland ice sheet is especially vulnerable to climate change. Arctic climate is believed to be now rapidly warming and much larger Arctic shrinkage changes are projected. The area of melting in 2002 broke all previous records. In 2006, estimated monthly changes in the mass of Greenland's ice sheet suggest that it is melting at a rate of about 239 cubic kilometers per year.
These measurements came from the US space agency's GRACE satellite. Recently, fears have grown that continued climate change will make the Greenland Ice Sheet cross a threshold where long-term melting of the ice sheet is inevitable. Such a rise would inundate almost every major coastal city in the world. How fast the melt would eventually occur is a matter of discussion.
Some scientists have cautioned that these rates of melting are overly optimistic as they assume a linear, rather than erratic, progression. The melt zone, where summer warmth turns snow and ice into slush and melt ponds of meltwater, has been expanding at an accelerating rate in recent years.
When the meltwater seeps down through cracks in the sheet, it accelerates the melting and, in some areas, allows the ice to slide more easily over the bedrock below, speeding its movement to the sea. Besides contributing to global sea level rise, the process adds freshwater to the ocean, which may disturb ocean circulation and thus regional climate.
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