The Heat Is Online

Do disappearing icebergs signal global warming?

Science Magazine Volume 285, Number 5424 Issue of 2 Jul 1999

Bernice Wuethrich

Unlike the Titanic, the Queen Elizabeth II is the most conservative of cruise ships when it comes to icebergs, if need be, sailing far south to avoid the bergs that normally pock the North Atlantic. But this spring the luxury liner crossed the notorious Iceberg Alley without a second thought. For reasons no one understands -- although global warming is a top suspect -- the Grand Banks shipping lanes, which are located southeast of Newfoundland, were an ice-free zone.

For the first time in 85 years, the International Ice Patrol (IIP) issued not a single bulletin reporting lurking bergs. "The lack of ice is remarkable," says IIP Commander Steve Sielbeck: The Coast Guard's IIP has been tracking icebergs that wander south of 48ºN latitude ever since the Titanic sank in 1912. And by now the trackers thought they knew what to expect. In an average year, some 500 bergs drift down the Labrador Coast from western Greenland, where most are spawned.

But the number varies widely, depending on a quasi-decadal cycle of high and low atmospheric pressures known as the North Atlantic Oscillation (NAO). High NAO years typically mean strong northwesterly winds that bring cold Arctic air to the Labrador Sea--and push convoys of icebergs toward the shipping lanes. Low NAO years usually coincide with low iceberg frequencies. This year, however, the NAO was high, but the winds inexplicably blew in from the northeast. "Something is out of sync," says Ken Drinkwater, an oceanographer at the Bedford Institute of Oceanography in Dartmouth, Canada.

The northeasterly winds stranded many icebergs against the Labrador coast, and because of unusually warm water and air, fewer than usual had drifted south in the first place. John M. Wallace, a meteorologist at the University of Washington, Seattle, notes that since the 1980s, winter temperatures have risen at least 0.5ºC poleward of 45º north, a line that runs through the Grand Banks. Until now, the chilling effect of westerly winds had masked this warming, which Wallace attributes to the general warming of the globe. This year, he says, "The decline of westerlies and global warming are working together."

The warmth melted sea ice, the frozen sea water that buffers icebergs from wave erosion and warmer water. This spring sea ice in the region was about as scarce as it has ever been, says Simon Prinsenberg, a research scientist at Bedford. Furthermore, water in the Grand Banks itself was 2ºC above normal--warm enough to instantly melt any remnant ice that kissed its border.

Despite all the heat, nobody is totally willing to discount the possibility that some kind of natural climate fluctuation is at play, albeit in a more extreme form than usual. Will the icebergs return next year? "Without a doubt," Sielbeck says. "I just can't tell you how far south they'll get."

Bernice Wuethrich is writer in Washington, D.C.

Science Volume 285, Number 5424 Issue of 2 Jul 1999