enlarge Gordon Hamilton/University of Maine

Leigh Stearns, a doctoral candidate at the University of Maine, installs a GPS instrument on Helheim Glacier in Greenland. Measuring the movement of glaciers is part of a climate study.

enlarge Leigh Stearns/University of Maine

Associate Professor Gordon Hamilton, right, of the University of Maine and Meredith Nettles of Columbia University install a GPS instrument on Helheim Glacier in Greenland.

Gordon Hamilton and Leigh Stearns used to come home from Greenland expeditions and study their glacier data without attracting a lot of attention or interest.

Not any more. Rapid melting of Greenland's glaciers and Arctic ice sheets is surprising scientists and making frequent headlines around the world.

Concerns about global warming have added much more urgency to the work of Hamilton and Stearns, who track the movement of massive glaciers that could ultimately carry enough ice into the Atlantic Ocean to raise sea levels thousands of miles away.

The researchers from the University of Maine's Climate Change Institute returned from their latest trip to southeastern Greenland in late August. With two federal grants totaling more than $700,000 coming their way, they are eager to return.

"That's going to allow us to go back and do what we've been doing the past few summers on a much grander scale," said Hamilton, a glaciologist and associate professor at UMaine.

The news from Greenland this summer is mixed, the researchers said. The glacier they focused on did not appear to be moving as fast as it was two years ago, when scientists first reported signs of an abrupt thaw; but it is still dumping ice into the ocean faster than its historic rate.

"We noticed some big changes in the front position just in the couple of months we were visiting this summer," Hamilton said.

Hamilton and Stearns, who is a doctoral candidate, drilled satellite transmitters into Helheim Glacier in southeastern Greenland and tracked its movement for two months before retrieving the equipment last month. They are among more than two dozen researchers based in Orono at the university's Climate Change Institute who travel around the globe, from Greenland to Antarctica, to find clues about the pace and effects of global warming.

The latest reminder of the urgency of that work came in headlines last week. Researchers studying Arctic ice sheets reported that the rate of thaw has been so great this summer that the Arctic Sea could be entirely ice-free in a little more than 20 years, well ahead of past projections.

News about the melting there has added to concern about the fate of polar bears that live on the ice, while also feeding interest in new summertime shipping routes and easier access to oil that's buried beneath the Arctic Sea.

Greenland's glaciers have been in the headlines since 2005, when Hamilton, Stearns and other researchers reported that some southern glaciers were shrinking and moving at startling rates. "Everything that we know about glaciers sort of changed in 2005," Hamilton said.

They reported then that the movement of the glaciers had accelerated from less than 4 miles per year to nearly 9 miles per year, or about half of a football field per day. The glaciers appear to have slowed down since then, but not to their historically glacial pace.

Glaciers are rivers of ice that slowly slide toward the ocean, depositing icebergs and fresh water into the sea. They historically have been recharged by snowfall at about the same rate they melt or break apart.

Scientists believe warming has accelerated the melting, creating pools of water beneath the glaciers and effectively speeding them up in the way a puddle of water helps an ice cube slide across a kitchen counter.

The Helheim Glacier was moving at an estimated five to six miles per year this summer, according to Hamilton and Stearns, though they have yet to process their data.

"The glacier hasn't quite stabilized itself yet," Hamilton said. "Maybe they accelerate into really fast speeds and then they slow down a little bit."

The trend is troubling because the ice sitting on Greenland is as much as 2 miles thick at its center and contains enough water to raise the level of the world's oceans 23 feet.

"Greenland matters," said Richard Alley, professor of geosciences at The Pennsylvania State University....