Clear link found between man-made gases and heating of oceans

Scientists have discovered the first unequivocal link between man-made greenhouse gases and a dramatic heating of the Earth's oceans.

The researchers - many of whom are funded by the US Government - have produced what they have described as a "stunning" correlation between a rise in ocean temperature over the past 40 years and pollution of the air with greenhouse gases.

In a study that destroys a central argument of global warming sceptics within the Bush Administration - that climate change could be a natural phenomenon - the scientists have produced the first clear evidence of man-made warming of the oceans.

The researchers say the dramatic findings should convince President Bush to drop his objections to the Kyoto treaty on climate change.

"This is perhaps the most compelling evidence yet that global warming is happening right now," said Tim Barnett, a marine physicist at the Scripps Institution of Oceanography in San Diego and a leading member of the team.

"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? How are we going to meet the challenges that are ahead of us?' " he added.

The findings are crucial because much of the evidence of a warmer world has until now focussed on air temperatures but it is the oceans that are the real driving force behind the Earth's climate, and yet little was known about how they have responded to the rise in greenhouse gases.

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

"We did look. We defined a fingerprint if you wish of ocean warming. Each of the oceans warmed differently at different depths and constitutes a fingerprint which you can look for," Dr Barnett told the American Association for the Advancement of Science in Washington DC.

"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," he said.

"We looked at the possibility that solar changes or volcanic effects could have caused the warming - not a chance. What just absolutely nailed it was greenhouse warming," he added.

America produces a quarter of the world's greenhouse gases yet under President Bush it is one of the few developed nations not to have signed up to the Kyoto treaty to limit emissions. The President's advisers have argued that the science of global warming is full of uncertainties and that climate change might just be a natural phenomenon.

However, Dr Barnett said this position is untenable because it is now clear from the latest study, which is yet to be published, that man-made greenhouse gases have caused vast amounts of heat to be soaked up by the oceans, generating a potentially unstable situation.

"In view of the fact that it is undeniable that global warming is going on and you can see it in the oceans, the evidence really is overwhelming, and it's a good time for nations that are not part of Kyoto to re-evaluate their positions and see if it would be to their advantage to join," he said.

The study involved scientists from the US Department of Energy, the Lawrence Livermore National Laboratory in California and the US National Oceanic and Atmospheric Administration, as well as climate scientists from the Met Office's Hadley Centre in Britain.

The scientists analysed more than 7 million recordings of ocean temperature measurements around the world, along with about 2 million readings of sea salinity, and compared the rise in temperatures at different depths to predictions made by two computer simulations of global warming.

"Two models, one from here and one from England, got the observed warming almost exactly. In fact we were stunned by the degree of similarity between the applications and the models," Dr Barnett said.

"If you take these results and combine them with a decade of earlier results, the debate about whether or not there is a global warming signal here and now is over for all intents and purposes, at least for rational people.

"The second thing it means is that the models are right. So when a politician stands up and says 'the uncertainty in all these simulations start to question whether we can believe in these models', that argument is not longer tenable," he said.

Typical ocean temperatures have increased since 1960 by between 0.5C and 1C, depending largely on depth, but it is not absolute temperature increases that are important but the total amount of heat that the oceans have soaked up in that period due to greenhouse warming.

"It turns out that [the atmosphere] is the worst place to look for a greenhouse signal although we live there. The real action is in the oceans," Dr Barnett said.

"The temperature is not the key. The real key is the amount of energy that has gone into the oceans. If we could mine the energy that has gone in over the past 40 years we could run the state of California for over 200,000 years.

"It's an amazing amount of energy that's gone in. Where did it come from? Not the Sun, satellites would have picked that up. It's come from greenhouse warming," he told the meeting.

Because the global climate is largely driven by the heat locked up in the oceans, a rise in sea temperatures could have devastating effects for many parts of the world - and not just the polar regions that are known to be melting. Freshwater supplies in many countries will be affected by the sort of climate change predictions made with the same two computer models that identified the link between greenhouse gases and ocean warming, he said.

"The new ocean study, taken together with the numerous validations of the same models in the atmosphere, portends far broader changes," he warned.

Ruth Curry, a marine scientist at the Woods Hole Oceanographic Institution, said that ocean warming could alter important warm-water currents like the Gulf Stream as melting glaciers pour massive volumes of freshwater into the North Atlantic.

"As the Earth warms, its water cycle is changing, in fact the water balance is being pushed out of kilter. These changes are happening now and they are expected to amplify in the 21st Century. It's a certainty that these changes will put serious strains on the ecosystems of the planet," Dr Curry said.

- INDEPENDENT