08 June 2005

Humans heat the oceans according to study

Human-caused global warming is measurably heating up the oceans, say US and UK researchers.

Calling on more than 7 million temperature readings from different depths in every ocean, the international team compared the realities over the past 40 years to predictions by computer climate models.

They discovered that the only way they could get the models to act like the real oceans was to add a human-induced greenhouse effect.

"I think this is the most compelling [data] yet," says Dr Tim Barnett of Scripps Institution of Oceanography at the University of California, San Diego.

Barnett is lead author of the paper, published in the current issue of the journal Science.

Barnett and his colleagues played devil's advocate with eight different computer climate models, tweaking them to try and see if they could make the warming trend appear in the oceans without a greenhouse effect.

But nothing worked.

"This present work is different in that it does not attempt to quantify this imbalance, but to attribute it to a specific cause," says Tim Boyer, oceanographer with the Ocean Climate Laboratory at the National Oceanographic Data Center.

A different approach
Previous studies have looked at ocean warming with more of an eye towards measuring it, says Boyer.

In fact, the oceans have been delaying the rapid increases in air temperatures from the greenhouse effect by absorbing a lot of heat, Boyer says.

The greenhouse effect is what happens when the atmosphere becomes richer in carbon dioxide and other gases that hold on to heat instead of letting it dissipate into space.

The danger of warming oceans is their unpredictability. Oceans operate as a heat sink; water retains heat longer than air, and oceans can also move heat into the depths, only to bring it back up decades or centuries later.

In the deep ocean, water may not return to the surface for thousands of years, says Boyer.

"If it returns to the surface in an area where the water is warmer than the air, heat will be released from the ocean to the atmosphere," he says.

For this reason, and others, it's hard to predict the exact climatic consequences of ocean heating, says Boyer.

What is certain, says Barnett, is that there will be consequences.

Source: abc.net.au


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