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 disruption of the Gulf Stream. By gathering warm air from the Gulf of Mexico and sending it to Europe, the Gulf Stream is responsible for keeping Britain, Scandinavia and other parts of Northern Europe warmer than their longitudinal equivalent, Labrador, Canada. Oceanographers fear that extra fresh water from the melting ice and increased rainfall might lower the salinity of the stream. Since this would reduce its density in the North Atlantic, the stream might not sink as abruptly as it does now, which would reduce its momentum and change its course--sending warm air to Greenland rather than Europe. Scientists don't believe this is likely to happen in the next century, but then again they're not positive it won't. "We think that it is something that deserves mention," says Alley. "Predicting weird things is hard to do."
Predicting how climate will change in specific regions is especially tricky. On Signy Island, off the Antarctic Peninsula, a group of researchers has been watching a dozen lakes over the last 20 years. By drilling holes in the lake ice and taking water samples, researchers have found that the lake water has warmed more than one degree Celsius in 15 years, much faster than the air temperature, which has warmed one degree in 40 years. In the amount of time it took the lakes to warm a degree or two, the island's seal population has soared from zero to about 25,000 and the amount of plant life in the lakes has increased fifteenfold. "This shows that, whatever changes our environment sustains, lakes will be affected even quicker," says Lloyd Peck of the British Antarctic Survey in Cambridge. It also means that a warmer earth might just make the South Pole more livable--fishing would be better, and you wouldn't need to expend so much energy just keeping warm. Never mind that Northern Europe might turn into a frozen tundra.
Before you buy that lakefront property in Antarctica, consider the possibility that the earth is heading into an ice age. For the past 10,000 years, the earth has been in a period of exceptionally mild and stable climate called the Holocene. Based on analyses of ice-age-era ice cut from Greenland, our luck may be coming to an end. For the last half million years, warm periods and ice ages have alternated according to a fairly regular pattern: 10,000 years of warmth followed by 90,000 years of cold. If the pattern holds, the next ice age should be along any time now. By polluting the atmosphere with greenhouse gases, perhaps we're staving off this fate. This could be the basis of a whole new outlook on global warming. Or perhaps it merely belongs with the other distant possibilities scientists haven't ruled out.