Ocean "Thermostat" May Be Secret Weapon Against Warming

Brian Handwerk
for National Geographic News
February 8, 2008

A natural but mysterious "ocean thermostat" may be limiting seawater warming in at least one Pacific Ocean locale.

The phenomenon may help protect some of the world's largest and most ecologically diverse coral reefs from the effects of climate change, a new study says.

"There appear to be natural negative feedbacks that keep water temperatures in check—at least in this part of the planet," said study co-author Joan Kleypas from the National Center for Atmospheric Research in Boulder, Colorado.

Kleypas and colleagues focused on the Western Pacific Warm Pool, a region in the open ocean northeast of Australia.

Water temperatures at the pool, which on average has been about the size of Australia, have risen little in recent decades, even as the rest of Earth's oceans have heated up.

"In the 20th century, warming has been less in that region, and coral bleaching has been less in that region," Kleypas said.

Coral bleaching occurs when warming waters cause corals to expel the colorful algae that sustain them. The corals turn a ghostly white and die in a few days unless temperatures cool down and the algae return.

"The model shows that there is a reason that the water is warming less—it's not just a fluke," Kleypas continued.

"The models and observations are showing the same thing, [which] points to some sort of mechanism or feedback process that is keeping temperatures in check."

Mysterious Process

Scientists have proposed several ways that the world's oceans might be able to regulate sea-surface temperatures.

One theory suggests that warming waters cause more evaporation, which in turn creates cooling cloud cover and prevalent winds.

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