Antarctica's massive coastal glaciers are quickly melting into the sea
as the oceans around the continent grow warmer - and the pace of ice
loss is speeding up.

An international satellite network measuring the thickness of the
glaciers as they shrink year by year has found that the glaciers have
melted so rapidly during the past 10 years that the continent is
losing almost as much ice as Greenland, according to researchers
gathering the satellite data.

The team from Chile, England and the Netherlands is led by Eric
Rignot, a radar engineer and glacier specialist at UC Irvine and
NASA's Jet Propulsion Laboratory who has watched the shrinking
glaciers and gathered data for the past 15 years from Canadian,
Japanese and European polar-orbiting satellites.

Those satellites carry radar instruments that can measure the
thickness of each glacier with remarkable accuracy, and they have now
mapped more than 85 percent of the entire coastline of Antarctica,
covering all the continent's major glaciers.

Unlike Greenland's coastal glaciers, where meltwater from the ice on
the surface seeps down to the base of each glacier and lubricates it
to speed its flow to the sea, the glaciers on Antarctica move down
from the land as huge ice sheets and spread out over the ocean, where
the thick glaciers are known as ice shelves.

For many years, scientists have watched some of these giant ice
shelves breaking apart and crashing into the sea, and now more and
more of them are melting as they move out over the ocean.

The cause: Antarctic waters like the Bellingshausen and Amundsen seas
are warming, and as their water temperatures rise they melt the
undersides of the ice sheets so the sheets become thinner and the seas
intrude farther and farther inland - to melt still more of the ice,
Rignot explained in a phone interview.

Although the effect of all this ice loss on global sea levels is still
small - measured in a rise of only a few thousands of an inch each
year so far from the melting in Antarctica - that increase has nearly
doubled in the past 10 years, he estimated.

"We're concerned that the rate of glacier melting will double
rapidly," Rignot said.

Ice loss is most pronounced in Antarctica's Pine Island Bay region,
where three major glaciers are losing ice fast, and on the northern
tip of the Antarctic Peninsula, Rignot and his colleagues reported.

Glaciers in those two regions alone lost about 212 billion tons of ice
from 1996 to 2006 - an amount very similar to the total loss of ice on
Greenland, Rignot and his team calculated.

The east coast of the Antarctic Peninsula is where two major ice
shelves - called Larsen A and Larsen B - disintegrated in 1995 and
2002. Those immense events were among the most convincing early
signals that global warming is real and dangerous.

The researchers calculated the increase in mass of the glaciers as
snow has piled up on them, and compared those numbers with the losses
due to melting into the sea. The calculations yield what Rignot and
his colleagues term the "ice sheet mass balance," and the overall
result is increasingly negative, they report.

"Large uncertainties remain in predicting Antarctica's future
contribution to sea level rise," Rignot said.

"The ice sheets are responding faster to climate change than (anyone)
anticipated," he said.

E-mail David Perlman at dperlman@....

This article appeared on page A - 2 of the San Francisco Chronicle

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/01/26/MN50UM20C.DTL