[graffis-l] greenland,ice and instability

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At 09:29 AM 1/8/08, you wrote:

>In Greenland, Ice and Instability

>Posted by: " Mark Graffis " mgraffis mgraffis

>Mon Jan 7, 2008 5:34 pm (PST)

>http://www.nytimes.com/2008/01/08/science/earth/08gree.html?_r=1 & ref=science & or\

ef=slogin

>

>January 8, 2008

>In Greenland, Ice and Instability

>By ANDREW C. REVKIN

>The ancient frozen dome cloaking Greenland is so vast that pilots have

>crashed into what they thought was a cloud bank spanning the horizon.

>Flying over it, you can scarcely imagine that this ice could erode fast

>enough to dangerously raise sea levels any time soon.

>

>Along the flanks in spring and summer, however, the picture is very

>different. For a lengthening string of warm years, a lacework of blue

>lakes and rivulets of meltwater have been spreading ever higher on the ice

>cap. The melting surface darkens, absorbing up to four times as much

>energy from the sun as unmelted snow, which reflects sunlight. Natural

>drainpipes called moulins carry water from the surface into the depths, in

>some places reaching bedrock. The process slightly, but measurably,

>lubricates and accelerates the grinding passage of ice toward the sea.

>

>Most important, many glaciologists say, is the breakup of huge

>semisubmerged clots of ice where some large Greenland glaciers,

>particularly along the west coast, squeeze through fjords as they meet the

>warming ocean. As these passages have cleared, this has sharply

>accelerated the flow of many of these creeping, corrugated, frozen rivers.

>

>All of these changes have many glaciologists “a little nervous these days

>— shell-shocked,” said Ted Scambos, the lead scientist at the National

>Snow and Ice Data Center in Boulder, Colo., and a veteran of both

>Greenland and Antarctic studies.

>

>Some fear that the rise in seas in a warming world could be much greater

>than the upper estimate of about two feet in this century made by the

>Intergovernmental Panel on Climate Change last year. (Seas rose less than

>a foot in the 20th century.) The panel’s assessment did not include

>factors known to contribute to ice flows but not understood well enough to

>estimate with confidence. All the panel could say was, “Larger values

>cannot be excluded.”

>

>A scientific scramble is under way to clarify whether the erosion of the

>world’s most vulnerable ice sheets, in Greenland and West Antarctica, can

>continue to accelerate. The effort involves field and satellite analyses

>and sifting for clues from past warm periods, including the last warm span

>between ice ages, which peaked about 125,000 years ago and had sea levels

>12 to 16 feet higher than today’s.

>

>The Arctic Council, representing countries with Arctic territory, has

>commissioned a report on Greenland’s environmental trends, to be completed

>before the 2009 climate-treaty talks in Copenhagen, at which the world’s

>nations have pledged to settle on a long-term plan for limiting

>human-caused global warming.

>

>Konrad Steffen, a University of Colorado glaciologist who has camped on

>the shoulders of Greenland’s ice sheet each year since 1990, is the lead

>author of the chapter in the report on Greenland’s climate. Last August,

>he and a team focusing on the ways meltwater might affect ice movement

>dropped a camera 330 feet down a water-filled moulin to explore whether

>the plumbing system can be mapped.

>

>Research on alpine glaciers shows that as more water flows through such

>apertures, ice can shift more quickly. But eventually large sewerlike

>conduits form, limiting the lubrication effect. The camera drop was only

>an initial test.

>

>Alberto Behar, a NASA engineer who designed the camera, said some

>unconventional methods were being considered to chart the flow of such

>water. “We had ideas to send rubber ducks down and see if they pop out in

>the ocean,” he said. “They’d have a little note saying, ‘Please call this

>number if you find me.’”

>

>The changes seen in Greenland may turn out to be self-limiting in the

>short run; surging glaciers can flatten out and slow, for instance. Or

>they may be a sign that the island’s ice — holding about the same volume

>of water as the Gulf of Mexico — is poised for a rapid discharge.

>Scientists are divided on that question, and on whether there is a

>near-term risk from a Texas-size portion of West Antarctica’s ice sheet

>that is also showing signs of instability. This split divides those

>foreseeing a rise in the sea level of a couple of feet this century from

>water added by Greenland, West Antarctica and mountain glaciers, and a few

>experts who speak of a couple of yards in that time.

>

>Those holding a more conservative view of Greenland’s near-term fate

>include Richard Alley of Pennsylvania State University, who noted that ice

>cores and tests of organic material from beneath the ice implied that the

>main mass of the Greenland ice sheet clearly endured thousands of years of

>warming in the past without vanishing.

>

>“It’s basically a big lump of ice sitting on this bedrock,” Dr. Alley said

>in describing Greenland’s behavior in warm conditions. “What it tries to

>do is snow more in the middle and melt more on the edges. If it pulls its

>edges back, then there’s less area to melt, and that helps it survive.

>That’s why you can have a stable ice sheet in a warmer climate.”

>

>But there is no significant debate on the long-term picture anymore.

>Should greenhouse-gas emissions follow anything close to a “business as

>usual” rise, the resulting warming and ice loss at both ends of the earth

>would cause coasts to retreat for centuries. While it was circumspect

>about near-term changes, the intergovernmental panel was confident about

>that long view.

>

>The prospect of having no “normal” coastline for the foreseeable future

>has many scientists deeply concerned.

>

>“What is at stake is the stability we have always taken for granted” both

>for coasts and climate itself, said Jason E. Box, an associate professor

>of geography at Ohio State University. Dr. Box presented fresh findings at

>the American Geophysical Union meeting last month showing that several

>Greenland glaciers accelerated sharply in direct response to warming, both

>in a warm spell starting in the 1920s and now.

>

>Eric Rignot, a longtime student of ice sheets at both poles for NASA’s Jet

>Propulsion Laboratory, said he hoped the public and policymakers did not

>interpret uncertainty in the 21st-century forecast as reason for

>complacency on the need to limit risks by cutting emissions.

>

>Dr. Rignot recently proposed that unabated warming could result in three

>feet of global sea rise just from water flowing off Greenland, three feet

>from Antarctica and 18 inches as the remaining alpine glaciers shrivel away.

>

>This is similar to projections by the most prominent NASA climate

>scientist, James E. Hansen, but more than twice the three-foot rise that

>many glaciologists seem to agree on as an outer bound for what is possible

>by the end of the century.

>

>“It is too early to reassure that all will stabilize, and similarly there

>is no way to predict a catastrophic collapse,” Dr. Rignot said. “But

>things are definitely far more serious than anyone would have thought five

>years ago.”

 

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