Already the Gulf Stream, which bathes the west coast of Britain in warm water from the Gulf of Mexico and keeps the country much milder than normal for such northern latitudes, is slowing down. Even greater melting of the Greenland ice could shut off the currents altogether, allowing depressions to dump snow rather than instead of rain in Britain and leading to a much colder continental climate, as has been experienced in the past week.

As happens on the eastern seaboard of Canada, which on the same latitude, the sea could freeze and snow lie for weeks or months instead of a day of two.

Last year large areas of the Greenland ice shelf, previously too high and too cold to melt, began pouring billions of gallons of fresh water into the northern Atlantic. Melted water trapped between the ice and the rock beneath is causing an acceleration of glaciers breaking off in huge chunks and increasing the number of icebergs.

According to scientists at the University of Colorado a very dramatic melting trend has been in progress since 1979. Extreme melt years were 1991, 1995 and 2002.

The Greenland ice sheet's maximum melt area increased on average by 16% from 1979 to 2002. This year's maximum melt extent of 264,400 square miles exceeds by 2.6 times the melt area measured in 1992. In particular, the northern and north-eastern part of the ice sheet experienced melting reaching up to an elevation of 2,000 metres (6,560ft).

This is the first time this area of the giant island, closest to the north pole, has suffered this kind of melting. The Colorado-based Cooperative Institute for Research in Environmental Sciences also found that temperatures during the summer of 2002 were unusually warm over much of the Arctic ocean.

"Since the season also was characterised by very stormy conditions, we believe these two factors contributed to extensive melt and break-up of the icepack," said research associate Mark Serreze, the lead author of the study, which was presented at a meeting of the American Geophysical Union.

Sea ice in the Arctic last year was at the lowest since satellite measurements began.

Mr Serreze said accelerated melting of sea ice, along with runoff from the Greenland ice sheet, was bad news for British weather moderated by the Gulf Stream. The warm water from the tropics now travels north past British shores and warms the western coastlines of Europe as far north as Norway before sinking to the bottom of the ocean and returning south.

This deep water convection in the north Atlantic has already been noted to be slowing down by British scientists, and US scientists say the trend could profoundly impact global ocean circulation and climate. "In other studies, changes in the north Atlantic circulation have been implicated in starting and stopping northern hemisphere ice ages," Mr Serreze said.

Climatologist Konrad Steffen, a professor of geography at Colorado, said a change in the Greenland climate towards warmer conditions would lead to an increase in the rate of sea level rise, mainly due to the dynamic response of the large ice sheet rather than just the surface melting.

"For every degree increase in the mean annual temperature near Greenland, the rate of sea level rise increases by about 10%," Professor Steffen said. Oceans are now rising by a little more than half an inch every 10 years.