WASSHINGTON: The first evidence of human-produced global warming in the oceans has been found, thanks to computer analysis of seven million temperature readings taken over 40 years to depths of 700 metres (2,300ft).

Tim Barnett, of the Scripps Institution in San Diego, told the American Association for the Advancement of Science in Washington on Friday that he was "stunned" by the findings, which have yet to be published in the scientific press.

"The statistical significance of these results is far too strong to be merely dismissed and should wipe out much of the uncertainty about the reality of global warning," he said.

In effect, US scientists financed by the government have once again told the Bush administration that global warming is real, and that humans were responsible. America pulled out of the Kyoto agreement, which came into force on Wednesday, under which many nations have agreed to reduce greenhouse gas emissions.

"Over the past 40 years there has been considerable warming of the planetary system and approximately 90% of that warming has gone directly into the oceans," Dr Barnett said. "So if you want to go and find out what's causing it, that's the place to look. We did look.

"We defined a fingerprint, if you wish, of ocean warming ... We had several computer simulations, for instance, one for natural variability. Could the climate system just do this on its own? The answer was clearly no."

The climate shift that affected the oceans would have other consequences. A dramatic acceleration of glacier melting in the Andes, and in western China, could leave millions of people without enough water each summer.

Climate warming would alter snow levels in the American mountains and precipitate a water crisis in the western US within 20 years. In the past four decades, other scientists told the conference, an extra 20,000 cubic kilometres of glacial ice had flowed into the sea, changing salinity levels and threatening to alter ocean flow patterns, with unpredictable consequences.

The warming of the Arctic could have a big impact on seals, polar bears and walruses, which depend on winter ice for hunting. In 1997, hundreds of thousands of short-tailed shear waters died because a bloom of plankton changed the colour of the water in Bering Strait and masked the birds' food supply.

There was evidence of a build-up of melt water below the Greenland ice sheet. If the ice cap melted, sea levels could rise by seven metres. "We've got a serious problem ahead of us. The debate is no longer: is there a global warming signal? The debate now is: what are we going to do about it?" Dr Barnett said. -Dawn/The Guardian News Service.