Global warming is already attacking the world's coral reefs and, if nothing is done soon, could begin a long-term assault on the vast West Antarctic Ice Sheet. If the ice sheet begins to disintegrate, the worldwide consequences over the next several centuries could well be disastrous.

Coral reefs are sometimes called the rain forests of the oceans because of the tremendous variety of animal and plant life that they support.

"They're the richest ocean ecosystem, and if they are destroyed or severely damaged, a lot of the biological diversity simply goes away," said Dr. Michael Oppenheimer, a professor of geosciences and international affairs at Princeton who is an expert on climate change.

Dr. Oppenheimer and Brian C. O'Neill, a professor at Brown, have an article in the current issue of Science magazine that addresses some of the long-term dangers that could result if nothing is done about global warming.

One of the things that is not widely understood about the greenhouse gases that are contributing to the warming of the planet is that once they are spewed into the atmosphere, they stay there for centuries, and in some cases, millenniums. So a delay of even a decade or so in reducing those emissions can make it much more difficult — and costly — to slow the momentum of the warming and avert the more extreme consequences.

In their article, Dr. Oppenheimer and Dr. O'Neill suggest that public officials and others trying to determine what levels of global warming would actually be dangerous could use the destruction of the world's coral reefs as one of their guides.

Coral reefs, which are breathtakingly beautiful natural phenomena, tend to thrive in water temperatures that are only slightly below the maximum temperature at which they can survive. There is not much margin for error. Even allowing for some genetic adaptation, a sustained increase in water temperatures of as little as a couple of degrees Fahrenheit can result in widespread coral reef destruction in just a few years.

A number of factors are already contributing to the destruction of coral reefs, and global warming is one of them. As the earth's temperature continues to rise, global warming will most likely become the chief enemy of what Dr. Oppenheimer calls "these wonderful sources of biological diversity."

The threat to coral reefs is clear and indisputable. Much less clear is the danger that global warming presents to the West Antarctic Ice Sheet.

"We really don't know with any level of certainty what amount of warming would destroy the ice sheet or how quickly that would happen," said Dr. Oppenheimer. He and Dr. O'Neill wrote, "In general, the probability is thought to be low during this century, increasing gradually thereafter."

There is not even agreement among scientists on the amount of warming necessary to begin the destruction. But what is clear is that if the ice sheet were to disintegrate, the consequences would be profound. So you don't want to play around with this. You want to make sure it doesn't happen.

"We know," said Dr. Oppenheimer, "that if the ice sheet were destroyed, sea levels would rise about five meters, which would be catastrophic for coastal regions. That would submerge much of Manhattan below Greenwich Village, for instance. It would drown the southern third of Florida, an area inhabited by about four million people."

Five meters is approximately 16 feet. Tremendous amounts of housing, wetlands and farming areas around the world would vanish. Large portions of a country like Bangladesh, on the Bay of Bengal, would disappear.

So what could actually set this potential catastrophe in motion? Dr. Oppenheimer has looked back at past geological epochs. "There is some evidence," he said, "that when the global temperature was warmer by about four degrees Fahrenheit than it is today the ice sheet disintegrated."

It is now estimated that if we do nothing to stem the rise of global warming, the increase in the earth's temperature over the course of this century will be between 3 and 10.5 degrees Fahrenheit. That is a level of warming that could initiate the disintegration of the ice sheet. And stopping that disintegration, once the planet gets that warm, may be impossible. 

Copyright 2002 The New York Times Company

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