Temperatures recorded this year in the upper 500 metres (1,625 feet) of sea in the Fram Strait -- the gap between Greenland and the Norwegian island of Spitsbergen -- were up to 0.6 C (1.08 F) higher than in 2003, they said in a press release received here.

The rise was detectable to a water depth of 2,000 metres (6,500 feet), "representing an exceptionally strong signal by ocean standards," it said.

The experts, from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, have been recording temperatures aboard a specialised vessel, Polarstern (Pole Star), for the past six weeks.

The sampling has been taking place in the West Spitsbergen Current, which carries warm water from the Atlantic into the Arctic Ocean.

The institute said water in the Fram Strait has been warming steadily since 1990 and over the past three years, satellite images had documented "a clear recession" of sea ice edges, both in the strait and the Barents Sea.

The latest data "point towards a further warming tendency," the institute said.

In June, a UN organisation announced that American scientists had detected an "alarmingly rapid growth" this year in airborne concentrations of carbon dioxide (CO2), the fossil-fuel pollutant blamed for global warming.

CO2 levels recorded in March 2004 at Hawaii measured 379 parts per million (ppm), an increase of three ppm over the previous year.

By comparison, there had been an annual increase of only 1.8 ppm over the past decade. Atmospheric concentrations of CO2 before the Industrial Revolution were 280 ppm.

The June announcement was made at a conference on renewable energies in Bonn by Joke Waller-Hunter, executive secretary of the UN Framework Convention on Climate Change (UNFCCC) -- the United Nations' paramount environment accord.

CO2 is the most important of the six "greenhouse" gases blamed for driving changes to the world's delicate climate system.

These gases hang like an invisible shroud in the atmosphere, trapping the Sun's heat and inflicting what many scientists predict will be serious changes to icecaps, glaciers and weather patterns.

In the Earth's distant past, climate change has occurred naturally, by emissions of CO2 disgorged by volcanoes and other phenomena.

But the overwhelming majority of climate experts say CO2 levels are rising fast today because of the unbridled burning of oil, gas and coal.

Opinions differ, though, as to how fast the effects will occur and how bad they will be.

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