By Andrew C. Revkin, The New York Times, Sept. 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.
Thin Glaciers Get Thinner in AntarcticaPlanetark.org, Sept. 27, 2004
WASHINGTON - Some of Antarctica's glaciers are melting faster than snow can replace them, enough to raise sea levels measurably, scientists reported.
Measurements of glaciers flowing into the Amundsen Sea, on the Pacific Ocean side of Antarctica, show they are melting much faster than in recent years and could break up.
And they contain more ice than was previously estimated, meaning they could raise sea level by more than predicted, the international team of researchers writes in the journal Science.
"The ... Amundsen Sea glaciers contain enough ice to raise sea level by 1.3 meters (4 feet)," the researchers wrote in their report.
"Our measurements show them collectively to be 60 percent out of balance, sufficient to raise sea level by 0.24 mm (nearly 0.01 inch) per year," they added.
And as the surrounding ice shelves melt - which they are doing - this process will speed up, the researchers said.
"The ice shelves act like a cork and slow down the flow of the glacier," said Bob Thomas of the NASA Goddard Space Flight Center's Wallops Flight Facility in Virginia.
Theirs is the second report this week to warn of rapidly melting glaciers in Antarctica.
On Tuesday a team at NASA and the University of Colorado reported that the 2002 breakup of the Larsen B ice shelf on the other side of the continent had accelerated the breakup of glaciers into the Weddell Sea.
Many teams of researchers are keeping a close eye on parts of Antarctica that are steadily melting.
Large ice shelves in the Antarctic Peninsula disintegrated in 1995 and 2002 as a result of climate warming. But these floating ice shelves did not affect sea level as they melted.
Glaciers, however, are another story. They rest on land and when they slide off into the water they instantly affect sea level.
"The rates of glacier change remain relatively small at present," said Eric Rignot of NASA's Jet Propulsion Laboratory in Pasadena, California, who worked on Friday's study.
"But the potential exists for these glaciers to increase global sea level by more than one meter (3 feet). The time scale over which this will take place depends on how much faster the glaciers can flow, which we do not know at present."
The measurements also show the glaciers are thicker than once believed. This means more melting and more rapid melting, Thomas said.
"Our measurements show an increase in glacier thinning rates that affects not only the mouth of the glacier, but also 60 miles to 190 miles inland," Thomas said in a statement.
The researchers from NASA, the Centro de Estudios Cientificos in Chile, the University of Kansas and Ohio State University wrote their estimates based on satellite data and measurements from a Chilean P-3 aircraft equipped with NASA sensors.
Experts say that overall sea levels around the world are going up by about 1.8 mm or 0.07 inch a year. About half of this comes from melting ice in glaciers.
The melting into the Amundsen sea is now more than the previous amount from all of Antarctica and more than the estimated contribution from Greenland, the researchers said.