Heated Debate

Climatologists have produced evidence that the earth's climate regulates itself, keeping temperatures from rising above a certain level. This calls into doubt the most-dire predictions of global warming.

"I cannot see how the planet can have a runaway greenhouse effect," says Veerabhadran Ramanthan, a climatologist at the Scripps Institution of Oceanography at La Jolla, California. Ramathan and his colleague William Collins studied the behavior of the ocean-atmospheric system over the Pacific during the 1987 El Niño. In this periodic event, naturally occurring changes in ocean currents cause the sea surface to warm by several degrees. The results of their study were published in the British journal Nature.

Ramanthan and Collins found that as the sea surface grew warmer, water vapor increased substantially in the air. In turn, huge clouds formed. As the clouds climbed to freezing altitudes, they turned into gigantic "anvils" reflecting sunlight away from the earth. Eventually, the cloud cover became so thick, so widespread, and so highly reflective that it shut out the sunlight over the ocean.

With the sunlight shut out, the cooling began, and the clouds dissipated. Then the process started over. Critics of computer models of the greenhouse effect have long argued that such a process would occur, but this is the first proof that it does occur.

Ramanthan says that the ceiling beyond which the ocean warms no further appears to be 90 degrees Fahrenheit on a monthly average. That's well below the 93 degrees predicted by some computer models of the greenhouse effect.

William A. Nierenberg, director emeritus of the Scripps Institution, contends that cloud formation may be only one of a number of feedback mechanisms that will limit global warming. "In fact," he told the New York Times, "the average global temperature change could be almost zero."