At the turn of the millennium, geophysicists studying gaseous bubbles trapped in a column of ice from Greenland made a remarkable -- and discomforting -- discovery.

The earth's climatic history appeared much more erratic than expected. Some fifteen thousand years ago, Greenland abruptly warmed by sixteen degrees within a period of about fifty years. In one particularly traumatic episode three thousand years later, the mean temperature in Greenland shot up by fifteen degrees in a single decade!

Tracing the record back to the last ice age, researchers were dismayed to find that, even as much of Europe and North America lay buried beneath glaciers, Greenland's temperature was oscillating wildly, sometimes in spikes of ten degrees, sometimes of twenty.

Indeed, Richard Alley, the geophysicist heading the National Academy of Sciences (NAS) panel on abrupt climate change, compared the climate to a freakish carnival ride:

"Dozens of rapid changes litter the record of the last hundred thousand years," he observed. "If you can possibly imagine the spectacle of some really stupid person (or, better, a mannequin) bungee jumping off the side of a moving roller coaster car, you can begin to picture the climate."

[Alley also once compared the climate to a light switch being toyed with by an impish three-year-old.]

[Amount by which melting Arctic ice was projected (in 2002) to shorten shipping routes between Europe and East Asia by 2020: 33 percent.]