Ice at the North Pole melted at an unprecedented rate last week, with leading scientists warning that the Arctic could be ice-free in summer by 2013.

Satellite images show that ice caps started to disintegrate dramatically several days ago as storms over Alaska's Beaufort Sea began sucking streams of warm air into the Arctic.

As a result, scientists say that the disappearance of sea ice at the North Pole could exceed last year's record loss. More than a million square kilometers melted over the summer of 2007 as global warming tightened its grip on the Arctic. Such destruction could now be matched, or even topped, this year.

"It is a neck-and-neck race between 2007 and this year over the issue of ice loss," said Mark Serreze, of the U.S.  National Snow and Ice Data Center in Boulder, Colorado. "We thought Arctic ice cover might recover after last year's unprecedented melting - and indeed the picture didn't look too bad last month. Cover was significantly below normal, but at least it was up on last year.

"But the Beaufort Sea storms triggered steep ice losses and it now looks as if it will be a very close call indeed whether 2007 or 2008 is the worst year on record for ice cover over the Arctic. We will only find out when the cover reaches its minimum in mid-September."