The Greenland ice sheet is, after Antarctica, the second biggest expanse of ice in the world.
Its fringes expand and contract with the seasons; but images show it is melting more each summer now than two decades ago.

16 Feb. 2006, By Paul Rincon BBC News science reporter:

Greenland's glaciers are sliding towards the sea much faster than previously believed. It was thought the entire Greenland ice sheet could melt in about 1,000 years, but the latest evidence suggests that could happen much sooner.

It implies that sea levels will rise a great deal faster as well. If the Greenland ice sheet melted completely, it would raise global sea levels by about 7 m.

Greenland's contribution to global sea level rise today is two to three times greater than it was in 1996.

Previous estimates suggested it would take many hundreds of years for the Greenland ice sheet to melt completely. The new data will cut this timescale, but by how much is uncertain.

In 1996, Greenland was losing about  100 cubic km per year in mass from its ice sheet.
In 2005, this had increased to about  220 cubic km.
Over the past 20 years, the air temperature in south-east Greenland has risen by 3C. Warmer temperatures cause more surface melt water to reach the base of the ice sheet where it meets the rock. This is thought to serve as a lubricant, easing the glaciers' march to the sea.

Arctic warming
Reuters reports on March 6, 2009 :

The Arctic is warming at twice the rate of the rest of the world and the sea-ice cover shrank to a record low in 2007 before growing slightly in 2008. Vincent's scientific team has spent the past 10 summers on remote Ward Hunt Island. In 2008 the maximum summer temperature on Ward Hunt hit 20 C compared with the usual 5 C.

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BBC News :    Glacier races to ocean             Arctic - Antarctic