Monday, June 26, 2006

Greenland's melting ice alarms scientists

We seem to have a much bigger problem than originally contemplated...

1 comment:

Martie said...

Greenland's melting ice alarms scientists
Robert Lee Hotz
Los Angeles Times

June 25, 2006

JAKOBSHAVN GLACIER, Greenland -- Glaciologist Jay Zwally knows the Greenland ice sheet in a way few could match. He has spent decades in the field, studying ice cores, watching the glacial march of the ice toward the sea.

But a recent flight over Greenland's biggest and fastest-moving outlet glacier revealed alarming changes. Mile upon mile of the steep fjord was choked with icy rubble from the glacier's disintegrated leading edge.

More than six miles of the glacier had crumbled into open water. Zwally was dismayed by how quickly the breakup had occurred.

Climate experts have started to worry that the ice cap is disappearing in ways that computer models had not predicted.

By all accounts, the glaciers of Greenland are melting twice as fast as they were five years ago, even as the ice sheets of Antarctica -- the world's largest reservoir of fresh water -- also are shrinking, researchers at NASA's Jet Propulsion Laboratory and the University of Kansas reported in February.

Since scientists started monitoring the weather at Swiss Camp in Greenland in 1991, the average winter temperature has risen almost 10 degrees. Last year, the annual melt zone reached farther inland and up to higher elevations than ever before.

The Greenland ice sheet -- 2 miles thick and broad enough to blanket an area the size of Mexico -- shapes the world's weather, matched in influence by only Antarctica in the Southern Hemisphere.

In the heart of the Greenland ice sheet, snow that fell a quarter of a million years ago is still preserved. Temperatures dip as low as 86 degrees below zero.

The ice is so massive that its weight presses the bedrock of Greenland below sea level, so all-concealing that only recently did scientists discover Greenland might be three islands.

Should all of the ice sheet thaw, the meltwater could raise sea level 21 feet and swamp the world's coastal cities, home to 1 billion people. It would cause higher tides, generate more powerful storm surges and, by altering ocean currents, drastically disrupt global climate.

Behavior turns erratic

Zwally and other researchers have focused their attention on a delicate ribbon: the equilibrium line, which marks the edge of frost and thaw in Greenland's seasonal balance.

The zone runs around the rim of the ice cap. Summer melting, on average, offsets the annual accumulation of snow.

Across the ice cap, however, the area of seasonal melting was broader last year than in 27 years of record-keeping, University of Colorado climate scientists reported. In early May, temperatures on the ice cap some days were almost 20 degrees above normal, hovering just below freezing.

From cores of ancient Greenland ice extracted by the National Science Foundation, researchers have identified at least 20 sudden climate changes in the past 110,000 years, in which average temperatures fluctuated as much as 15 degrees in a decade.

The increasingly erratic behavior of the Greenland ice has scientists wondering whether the climate, after thousands of years of relative stability, may again start oscillating.

Computer predictions fail

For those assessing the effect of global warming, there may be no more perfect place than this warren of red tents on the Northern Hemisphere's largest ice cap. Here, the theoretical effects seen in computerized climate models take tangible form.

University of Colorado climatologist Konrad Steffen set up Swiss Camp 155 miles north of the Arctic Circle in 1990 to study the weather along the equilibrium line. As a precaution, Steffen, 54, built the camp on a plywood platform to keep it afloat when the ice turns into summer slush and open lakes before refreezing in the fall.

Zwally joined his colleagues there May 8 in the regular spring migration of scientists to the Arctic. He has been coming to Swiss Camp every year since 1994 and has been studying the polar regions since 1972, monitoring the polar ice through satellite sensors. Eventually he realized he had to study the ice firsthand.

The ice sheet seemed such a stolid reservoir of cold that many experts had been confident it would take centuries for higher temperatures to work their way thousands of feet down to the base of the ice cap and undermine its stability.

By and large, computer models supported that view, predicting that as winter temperatures rose more snow would fall across the dome of the ice cap. Thus, by the seasonal bookkeeping of the ice sheet, Greenland would neatly balance its losses through new snow.

Indeed, Zwally and his colleagues in March released an analysis of data from two European remote-sensing satellites showing the amount of water locked in the ice sheet had risen slightly between 1992 and 2002.

Then the ice sheet began to confound computer-generated predictions.

By 2005, Greenland was beginning to lose more ice volume than anyone had anticipated -- an annual loss of up to 52 cubic miles a year -- according to more recent satellite gravity measurements released by JPL. The volume of freshwater ice dumped into the Atlantic Ocean has almost tripled in a decade.

Ice flows faster

Most of the computer models on which climate predictions are based did not take the dynamics of the glaciers into account.

Contrary to appearances, the monolith of ice is constantly on the move. Swiss Camp has been rafting on the ice stream toward the sea, on average, about 1 foot every day. Since Steffen pitched the main tents, the camp has moved about a mile downhill.

When Zwally started tracking the velocity of the ice with Global Positioning System sensors in 1996, the ice flow maintained a steady pace all year.

But he soon discovered that the ice around Swiss Camp had abruptly shifted gears in the summer, moving faster when the surface ice started to melt. By 1999, the ice stream had almost tripled its speed to about 3 feet a day.

In an influential paper published in the journal Science, Zwally surmised that the ice sheets had accelerated in response to warmer temperatures, as summer meltwater lubricated the base of the ice sheet and allowed it to slide faster toward the sea.

In a way no one had detected, the warm water made its way through thousands of feet of ice to the bedrock -- in weeks, not decades or centuries.

"This meltwater acceleration is new," Zwally said. "The significance of this is that it is a mechanism for climate change to get into the ice."

University of Texas physicist Ginny Catania pulled an ice-penetrating radar in a search pattern around the camp, seeking evidence of any melt holes or drainage crevices that could so quickly channel the hot water of global warming deep into the ice.

To her surprise, she detected a maze of tunnels, natural pipes and cracks beneath the unblemished surface.

"I have never seen anything like it, except in an area where people have been drilling bore holes," Catania said.

Since 2002, Greenland's three largest outlet glaciers have started moving faster, satellite data show.

On the eastern edge of Greenland, the Kangerlussuaq Glacier, like the Jakobshavn, has surged, doubling its pace. To the west, the Helheim Glacier now appears to be moving about half a football field every day.

In all, 12 major outlet glaciers drain the ice sheet the way rivers drain a watershed, setting the pace of its release to the ocean. If they all slide too quickly, there is a possibility that, perhaps decades from now, they could collapse suddenly and release the entire ice sheet into the ocean.

The Los Angeles Times is a Tribune Publishing newspaper.

shorter version ran in Final Edition

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