Fri Sep 24, 2004 6:20 am by Indy11
Antarctic Glaciers Quicken Pace to Sea; Warming Is Cited
By ANDREW C. REVKIN
Published: September 24, 2004
Spurred by warming coastal air and waters, some of Antarctica's glaciers have accelerated their seaward march, fresh observations show, suggesting that ocean levels might be irreversibly on the rise for centuries to come.
Global warming from smokestack and tailpipe emissions of heat-trapping gases could well be contributing to the changes, but some of what is happening is probably a delayed reaction to the long warm-up since the last ice age, glaciologists said yesterday.
Over all, Antarctica still holds a mix of conditions, with some spots cooling and others warming, but the new observations, described this week in three scientific papers, confirm that warming along the coast, as it causes fringes of ice to melt, can release larger ice sheets to flow faster to the ocean, where they will inevitably melt.
The changes were detected by separate satellite and aircraft surveys of small glaciers along the east side of the Antarctic Peninsula, the rugged, sharply warming arm reaching toward South America, and along giant ice sheets feeding into the Amundsen Sea.
In each place, the removal or weakening of fringing shelves of ice attached to the shore or seabed in front of the glaciers appears to have liberated the great inland ice sheets.
Similar shifts have been measured in some glaciers in Greenland, with erosion of "tongues" of ice protruding into the sea causing inland ice sheets to flow more quickly to the sea.
Even with the acceleration, the potential rise in seas in this century would probably remain within the range estimated by the main international panel studying global warming, perhaps two feet or so, said some of the scientists monitoring Antarctica.
That change already constitutes a slow-motion catastrophe for places like Bangladesh, New Orleans and low island nations, experts say. But the findings add weight to the idea that rising seas could be a fact of life for centuries to come, requiring serious reassessments of the human penchant for living along coasts.
In a paper published today in the online edition of the journal Science, one team said the vast glaciers flowing into the Amundsen Sea were thinning twice as fast near the coast as they had in the 1990's.
This is important because these glaciers help drain the West Antarctic Ice Sheet, a region containing enough ice to raise sea levels 20 feet.
The changes in these glaciers could be a delayed response to the departure of coastal ice shelves there in the prolonged warming since the last ice age, experts not associated with the study said. But the speed-up could also have been affected by recent further warming of the air and seas in the western Antarctic, some of which is probably linked to warming of the global climate from gas emissions, independent experts and study authors said.
Warmer seawater erodes the bond between coastal ice and the bedrock below, "like weakening the cork in a bottle," said Dr. Robert H. Thomas, a glacier expert for NASA in Wallops Island, Va., the lead author of the Science paper. "You start to let stuff out."
A pair of papers published this week in the journal Geophysical Research Letters described strong additional evidence that coastal changes can speed the flow of inland glaciers, focusing on the east coast of the Antarctic Peninsula.
That region captured worldwide attention in 2002 when the floating Larsen B ice shelf, the size of Rhode Island and locked to the shore since the last ice age, abruptly disintegrated into a constellation of icebergs.
In subsequent flights over inland glaciers, American and Argentine scientists measured a two-fold to six-fold increase in their speed in the following months, the researchers said. Satellite measurements showed some glaciers there slumped as much as 100 feet over the same span.
Adjacent glaciers not fronted by the departed shelf did not react, providing something rare in earth science, the equivalent of a case-control study, said Dr. Theodore A. Scambos, lead author of one of the papers on the changes along the peninsula and a glaciologist at the National Snow and Ice Data Center in Boulder, Colo.
Dr. Richard B. Alley, an expert on Antarctica at Pennsylvania State University who was not involved but is familiar with the findings, said the studies were cause for concern and justified a much more intensive survey of the world's thawing places.
In the best case, Dr. Alley said, there could be a short-term rise in sea levels that would stop as new fringing ice shelves eventually put the brakes on the glaciers. But it was also possible that conditions would set off "complete or near-complete collapse over centuries or millennia," he said, guaranteeing a steady flooding of coastlines far into the future.
Edited by - Indy11 on 9/24/2004 7:20:45 AM
