Ocean "Thermostat" May Be Secret Weapon Against Warming

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Warmer waters could also alter the flow of ocean currents and initiate an influx of cooler water in certain areas.

The controversial thermostat theory holds that an undefined process will naturally prevent sea-surface temperatures from rising above 88 degrees Fahrenheit (31 degrees Celsius) in the open oceans.

This is good news for corals in warm waters, such as those that live in the Western Pacific Warm Pool, where the average temperature is about 85 degrees Fahrenheit (29 degrees Celsius).

That's because stable water temperatures—rather than any specific temperature—are what reefs need to survive, said coral expert Nancy Knowlton of the Smithsonian Institution's National Museum of Natural History.

"In general, if the temperature gets above a degree Centigrade [two degrees Fahrenheit] over the normal seasonal maximum, coral reefs are often in trouble," she said.

(Knowlton, who was unaffiliated with the new study, is a National Geographic Committee for Research and Exploration grantee. National Geographic News is owned by the National Geographic Society.)

Warm-water corals will experience less drastic changes than their cold-water counterparts if an ocean thermostat is in effect.

(Related news: "Corals May Have Defense Against Global Warming" [October 4, 2007].)

The new research, which will appear tomorrow in the online edition of the journal Geophysical Research Letters, lends support to the thermostat theory.

The team's analysis of historical data combined with computer simulations show that the pool has warmed up only half as much as colder ocean regions.

With little idea of how the effect operates, it is unknown if such a thermostat is unique to the Western Pacific Warm Pool.

Such a process may be more widespread and either remain undetected or be overwhelmed by a larger and more complex mix of other climate drivers in waters nearer continental landmasses.

The effect's apparent beneficial impact is likely to draw much more attention to the Western Pacific Warm Pool and its reefs.

"It means that these kinds of places might be high-priority places to protect," the Smithsonian's Knowlton said.

Ancient Regulator

Study author Kleypas and colleagues also say that the pool's thermostat process may have been at work for a long time.

Evidence from the paleontological record suggests that the pool's water temperatures were not much warmer in the past—even during the Cretaceous period, which had higher-than-present levels of the greenhouse gas carbon dioxide (CO2).

But those ancient climates were more stable, and the team's computer models suggest that the projected rates of carbon entering the atmosphere—and subsequent warming—could overwhelm the regulating effect.

"The bad news is that we did look at some existing runs where [our modeled increase in atmospheric CO2] was pretty strong, and we did not see an effective thermostat," Kleypas said.

While the research raises more questions than it answers, Kleypas said, it provides a hopeful path to pursue.

"It's about solutions to deal with global warming," she said.

"It gives us some hope that these feedbacks exist, and we should be paying attention."

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