Nov. 21, 2005 — The latest surveys of large glaciers in Greenland have exposed an alarming step-up in melting that threatens to raise global sea levels far faster than the best climate models have predicted.

The latest data comes from a satellite study of the Helheim glacier, one of Greenland's largest ice outlets to the North Atlantic Ocean.

Helheim glacier is both flowing faster than ever and rapidly retreating from the sea. The two changes are intertwined — as the glacier recedes, the bulk that once created an upstream logjam of ice is gone, so the ice moves down into the fjord faster than ever.

"The really pertinent analogy is a floodgate on a dam," says Ian Howat, a doctoral Earth sciences student at of the University of California at Santa Cruz.

Howat and his colleagues studied satellite imagery, which shows that from the 1970s to 2000 the front of the Helheim glacier stayed put: The ice calving off into the sea was replaced by the glacier itself shifting steadily down the fjord.

In 2001, however, the glacier began retreating from the sea and shrinking back up the fjord. From 2001 to 2005 Helheim retreated 4.5 miles, ramping up from a rate of 70 feet per day to 110 feet per day.

What's worse, the ice is thinning: Since 2001, the surface of the glacier has dropped 130 feet.

"It's basically zooming up the fjord," says Slawek Tulaczyk, Howat's faculty advisor and a coauthor in a report on the changes in Helheim Glacier, which appears in the latest issue of Geophysical Research Letters.

The fact that Helheim Glacier and at least two other major Greenland glaciers are retreating more quickly screams to scientists that there is a common cause."

There has to be a trigger," says Tulaczyk. The most likely trigger is the already documented temperature increases in that region, which reflect climate change worldwide, he says.

Just as worrisome as the melting glaciers, however, is the inability of climate models to take the changes into account, says Tulaczyk.

At the moment, most climate models divide and simulate Earth in 15- to 20-mile-wide squares. They can't see Greenland's glaciers, which are only about 3.5 miles wide, he explained.

Worse, says Howat, is that traditional climate models treat glaciers and the Greenland ice sheet as a big ice cube that melts slowly and steadily as the climate warms.

The models do not take into account sudden rapid changes that speed up the glaciers and drain away ice for many miles inland. The quickening flow of Helheim glacier, for instance, has already propagated 12.5 miles inland, he says.

"The common thinking is that the large ice sheets respond over long time scales," says glaciologist Gordon Hamilton of the University of Maine.

Hamilton has personally measured changes in Helheim and other Greenland glaciers with GPS equipment. "But now, (the glaciers) show they respond within a fraction of a decade. It's a paradigm change."

It's also really bad news for people in coastal areas worldwide.

"The best models now show a few centimeters (sea level rise) over our lifetimes," says Hamilton. But because they neglect to account for what's being seen today in Greenland, "those predictions are wildly inaccurate."

If all of Greenland's ice sheet were to melt, it would raise global sea levels from between 15 to 20 feet. What fraction of that water is now pouring out through Helheim and other glaciers remains to be seen.