State Of The Ice.(melting polar ice caps and climatology)(Brief Article)

The conventional wisdom about global warming holds that the polar ice caps are melting. Enormous chunks of ice will break off the Antarctic mainland and float into the sea to melt, sending water levels rising around the world, inundating seaside cities and submerging islands. But recently, glaciologist Ian Joughin at the Jet Propulsion Laboratory in Pasadena, California, threw even that basic theory into question. After analyzing satellite data, he concluded that a massive ice sheet along the Ross Sea in Antarctica is not losing 20 billion tons of ice each year, as previously thought, but is in fact gaining 26 billion tons a year. The thickening, caused by a slowing of the streams that transport chunks of ice toward the sea, is probably due not to global warming but to the glacier's own "internal clock."

So goes the inexact science of climate change. Scientists trying to plumb the mysteries of global warming have been drawn to the poles, not only because they are extremely sensitive to climate swings, but also because their ice packs constitute a climatological record going back hundreds of thousands of years. Unfortunately, what they find there is far less clear-cut than the chunks of ice they send back to their labs. Climate experts generally agree that the earth has been warming and that greenhouse-gas emissions have had something to do with it. But decades of research show that the subject of climate change is vast and, for the moment, unfathomable. "I will actually yell at any student who claims to be telling the truth with a capital T," says Richard Alley of Pennsylvania State University's Department of Geosciences. "If they say that, they're not doing science anymore."

Ice melting is not even the most important area of disagreement. Another premise of global warming has been that the earth would warm at a steady, slow rate over time. But late last year, America's National Academy of Sciences warned of something called "abrupt climate change"- -swings in climate that occur in a decade or two, rather than over centuries. Alley, the report's lead author, likens rapid changes to flicking on a light switch; gradual changes, he says, are like moving a dial. "The whole earth system has switches and it has dials," he says. "Most of our models, most of our thinking, worries about the dials [gradual climate change]. But somewhere out there, there really are switches." The last time the earth witnessed a switch effect was 11,500 years ago, when Greenland's average temperature rose 10 degrees Celsius in 10 years. "Basically, every living thing at that time would have noticed that the world had changed," says Alley.

Scientists have identified one potentially dangerous switch. It would involve the ...