Antarctica's Amundsen Sea, seen in this 2002 satellite image, is covered by ice shelves that act as a buffer between the open ocean and the West Antarctic Ice Sheet.

HOUSTON - A Texas-sized area of Antarctica is thinning and could cause the world's oceans to rise significantly in the long-term, polar ice experts said in wrapping up a three-day conference.

"Surprisingly rapid changes" are occurring in Antarctica's Amundsen Sea Embayment, an ice drainage system that faces the southern Pacific Ocean, the experts said in a statement, adding that more study was needed to determine how fast it was melting and how much it could cause sea levels to rise.

The warning came Wednesday at the end of a conference of U.S. and European polar ice experts at the University of Texas in Austin.

The scientists blamed the melting ice on changing winds around Antarctica that are causing warmer waters to flow beneath the ice shelves in the Amundsen Sea. The shelves hold back ice that is grounded on the continent and known as the West Antarctic Ice Sheet. Should the shelves collapse, grounded ice would start flowing into the sea much more rapidly, raising sea levels.

The wind change, they said, appeared to be the result of several factors, including global warming, ozone depletion in the atmosphere and natural variability.

The thinning in the two-mile-thick West Antarctic Ice Sheet is being observed mostly from satellites, but it is not known how much ice has been lost because data is difficult to obtain in the remote region, they said.

"The place where the biggest change is occurring is the Amundsen Sea Embayment," said Donald Blankenship of the University of Texas Institute for Geophysics.

"One, it's changing, and two, it can have a big impact," he said in a Webcast with a number of conference participants.

The West Antarctic Ice Sheet contains enough grounded ice to raise world sea levels close to 20 feet, the scientists said.

Other parts of the continent also were losing ice, Blankenship said, but generally not as quickly. The much larger East Antarctic Ice Sheet is considered much more stable.

The statement listed a number of consensus points reached at the workshop, among them:

• "Satellite observations show that both the grounded ice sheet and the floating ice shelves of the Amundsen Sea Embayment have thinned over the last decades.
• "Ongoing thinning in the grounded ice sheet is already contributing to sea-level rise.
• "The thinning of the ice has occurred because melting beneath the ice shelves has increased, reducing the friction holding back the grounded ice sheet and causing faster flow."

"All of the ice on Earth contains enough water to raise sea level over 200 feet, with about 20 feet from Greenland and almost all of the rest from Antarctica," the scientists said in their statement. "Although complete loss of the Antarctic Ice Sheet is not expected, even a small change would matter to coastal populations."

The experts stressed that further research should be made a priority, noting that the U.N. Intergovernmental Panel on Climate Change, in its landmark report last February, "could not provide a best estimate or an upper limit on the rate of sea-level rise in coming centuries because of a lack of understanding of the flow of the large ice sheets."

Background on the conference is online at: www.jsg.utexas.edu/walse/