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Wednesday, August 18, 2010

Jason Box: Of Greenland's 30 widest glaciers, the northern-most ones are losing the most ice (Petermann, Helheim, etc.)

Researchers race to catch up with melting, shifting Polar realities

When the Petermann Glacier calved an ice island four times the size of Manhattan earlier this month, GPS sensors embedded in the ice and time-lapse cameras sitting on nearby rock were watching. 

But scientists who put them there were caught off guard. Traveling to northwestern Greenland to retrieve the data that equipment recorded will cost them roughly $93,000, money they currently don't have.

That's unfortunate, says Jason Box, a climate scientist at Ohio State University who helped place those instruments, because the difficulty comes as his research team has made a startling discovery. Of the 30 widest glaciers in Greenland, it's the ones in the north -- where Petermann is located -- that are collectively losing the most ice.

"The science really hasn't caught up with the observations," he said of those results, which he will present at a scientific meeting this week in Ohio. "The observations are showing really dramatic changes. There is an element of surprise. The fact that there is so much change in northern Greenland is not something the community is aware of yet."

Box's dilemma illustrates the difficulty and expense of operating in harsh polar environments, factors that can magnify sheer bad luck. (Scientists set up their monitoring of the Petermann Glacier last summer, when they expected it to calve at any moment.) But the story of the recent calving also offers a window into the intense, ongoing effort by scientists who study the world's ice to improve their understanding of how melting at the poles will contribute to sea level rise.

"One of the major impacts [of the calving] will be that we expect Petermann Glacier ... to speed up, something like a factor of two, because glaciers always speed up when ice shelves break off in front of them," said Robert Bindschadler, a senior research scientist at the University of Maryland, Baltimore County, at a recent congressional briefing. "That's an expected consequence. And that's going to increase the drainage of the Greenland ice sheet and contribute to a rise in sea level."

Predicting sea level rise: a high-stakes game

But just how quickly the massive freshwater ice sheets in Greenland and Antarctica will melt is still uncertain. And that uncertainty carries over into projections of how high and how fast the world's seas will rise.

Just three years ago, the Intergovernmental Panel on Climate Change predicted seas would rise between 7 and 23 inches by 2100 -- but couched that estimate with a giant caveat. The IPCC cautioned that an additional rise could come from rapid and unpredictable melting in Greenland and Antarctica, which it didn't attempt to estimate.

"The terminology in a football game is, we punted," said Pennsylvania State University glaciologist Richard Alley, one of the scientists who worked on that portion of the IPCC's wide-ranging fourth assessment report. "We didn't know what to do."

Now scientists are scrambling to play catch-up amid high stakes. Greenland's ice alone contains enough fresh water to raise the world's seas by 23 feet.

Reconstructions of the Earth's past climate indicate that a temperature rise of roughly 2-7 °C could cause the Greenland ice sheet to melt entirely, Alley said.

"What we find from looking at history -- when the world warms, the Arctic warms more," he said, citing a 2008 federal report on abrupt climate change that he helped author. "When the Arctic warms, Greenland melts."

Scientists don't believe the Greenland ice sheet will disappear anytime soon. But if greenhouse gas emissions go unchecked, Earth's climate could reach a tipping point in a decade that would put Greenland's ice on a course to disappear within centuries, Alley said.

Satellite measurements show the margins of the Greenland and Antarctic ice sheets are thinning, driven primarily by the acceleration of outlet glaciers like Petermann.

"As the Earth is getting warmer, ice sheets are going to shrink and sea level will go up," Bindschadler said. "There is no doubt about it. The key question for experts such as myself are these: How much will sea level go up, and when is that going to happen? That's where research is going right now."
''1 meter and beyond''

Right now, researchers' best estimate of how high seas will rise by the end of the century is "1 meter and beyond," or roughly 3 feet, the scientist said. But such estimates still carry a large dose of uncertainty, which makes monitoring events like the Petermann calving so important, he added.

Researchers have gotten a better handle on the factors that influence an ice sheet's behavior. They've learned that melt ponds that form on top of the ice can worsen cracks in an ice shelf or quickly drain to the bedrock below an ice sheet, greasing its march to the sea.

They've also discovered warm ocean water circulating under ice shelves that support the tongues of glaciers at the mouth of the sea, melting the ice from below. When those ice shelves disintegrate, the glaciers slide faster into the water.

The question now is how to incorporate that knowledge into computer models of climate change.

"Even in the scientific community, people think, 'Why are ice sheets so damned hard?' " said David Vaughan, a British Antarctic Survey researcher who is coordinating an E.U.-funded €10 million research program to improve sea level rise projections.

His short answer: There aren't as much data on ice sheet behavior over time as scientists would like to have to test their models.

"We know very little about how ice sheets have changed over the past 1,000 years," said Vaughan, adding that satellites and new monitoring systems in the ocean are slowly helping to improve the situation.
''Missing the big action''

Some of that is just attributable to bad luck. In the 1970s, U.S. researchers had a "hugely active" program monitoring the movement of ice through the western Antarctic ice sheet's Ross Ice Shelf. European researchers focused on the Ronne Ice shelf. But almost no one was paying attention to ice lost through the Amundsen Sea, where warming has taken a heavy toll in recent years.

"It only became blindingly apparent that we were missing it when the first satellite assessments of ice thickness changes became available in 1998," Vaughan said.
"Neither program was wasted ... but we were missing the big action."

Looking into the past is also difficult because when ice sheets advance, they wipe out the sediment or bedrock below them that contains information about past ice sheet retreat.

Despite those difficulties, Vaughan is working with scientists from 24 European research institutions to improve ice sheet models and sea level rise projections. The project, called "ice2sea," is due to complete its work in 2012, just in time to be included in the next IPCC report.

Meanwhile, at Ohio State, Jason Box has been working the phones to secure the cash to travel to Greenland and retrieve the data from his cameras and sensors.

One of his colleagues estimated that making the trip would require reserving about 30 hours of air charter time at just under £2,000, or $3,100, per hour. That's enough to chopper researchers to Petermann Glacier and give them three hours on the ice.

"It's really expensive to get to Petermann. It's about as remote as you can get," Box said. "We've got cameras at other glaciers a lot closer to airports and stuff. We have to weigh our options carefully. It's kind of a game, glaciology. ... We could see the writing on the walls of Petermann. There was going to be a breakup. It was just a matter of time."

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