Sea Levels Likely to Rise Much Faster Than Was Predicted

>From <www.commondreams.org>

Published on Friday, February 17, 2006 by the Independent/UK
Sea Levels Likely to Rise Much Faster Than Was Predicted
by Steve Connor

Global warming is causing the Greenland ice cap to disintegrate far faster
than anyone predicted. A study of the region's massive ice sheet warns that
sea levels may - as a consequence - rise more dramatically than expected.
Scientists have found that many of the huge glaciers of Greenland are moving
at an accelerating rate - dumping twice as much ice into the sea than five
years ago - indicating that the ice sheet is undergoing a potentially
catastrophic breakup.

The implications of the research are dramatic given Greenland holds enough
ice to raise global sea levels by up to 21ft, a disaster scenario that would
result in the flooding of some of the world's major population centres,
including all of Britain's city ports.

Satellite measurements of the entire land mass of Greenland show that the
speed at which the glaciers are moving to the sea has increased
significantly over the past 10 years with some glaciers moving three times
faster than in the mid-1990s.

Scientists believe that computer models of how the Greenland ice sheet will
react to global warming have seriously underestimated the threat posed by
sea levels that could rise far more quickly than envisaged.

The latest study, presented at the American Association for the Advancement
of Science, in St Louis, shows that rather than just melting relatively
slowly, the ice sheet is showing all the signs of a mechanical break-up as
glaciers slip ever faster into the ocean, aided by the "lubricant" of melt
water forming at their base.

Eric Rignot, a scientist at the Jet Propulsion Laboratory and the California
Institute of Technology in Pasadena, said that computer models used by the
UN's International Panel on Climate Change have not adequately taken into
account the amount of ice falling into the sea from glacial movements.
Yet the satellite study shows that about two-thirds of the sea-level rise
caused by the Greenland ice sheet is due to icebergs breaking off from
fast-moving glaciers rather than simply the result of water running off from
melting ice.

"In simple terms, the ice sheet is breaking up rather than melting. It's not
a surprise in itself but it is a surprise to see the magnitude of the
changes. These big glaciers seem to be accelerating, they seem to be going
faster and faster to the sea," Dr Rignot said.

"This is not predicted by the current computer models. The fact is the
glaciers of Greenland are evolving faster than we thought and the models
have to be adjusted to catch up with these observations," he said.
The Greenland ice sheet covers an area of 1.7 million sq km - about the size
of Mexico - and, in places, is up to 3km thick. It formed over thousands of
years by the gradual accumulation of ice and snow but now its disintegration
could occur in decades or centuries.

Over the past 20 years, the air temperature of Greenland has risen by 3C and
computer models suggested it would take at least 1,000 years for the ice
sheet to melt completely. But the latest study suggests that glaciers moving
at an accelerating rate could bring about a much faster change.

"The behaviour of the glaciers that dump ice into the sea is the most
important aspect of understanding how an ice sheet will evolve in a changing
climate," Dr Rignot said. "It takes a long time to build and melt an ice
sheet but glaciers can react quickly to temperature changes. Climate warming
can work in different ways but, generally speaking, if you warm up the ice
sheet, the glacier will flow faster," he said.

The ice "balance sheet" of Greenland is complex but - in simple terms - it
depends on the amount of snow that falls, the amount of ice that melts as
run-off and the amount of ice that falls directly into the sea in the form
of icebergs "calving" from moving glaciers.

Satellites show that the glaciers in the south of Greenland are now moving
much faster than they were 10 years ago. Scientists estimate that, in 1996,
glaciers deposited about 50 cubic km of ice into the sea. In 2005 it had
risen to 150 cubic km of ice.

Details of the latest study, published in the journal Science, show that
Greenland now accounts for an increase in global sea levels of about 0.5
millimetres per year - compared to a total sea level rise of 3mm per year.
When previous studies of the ice balance are taken into account, the
researchers calculated that the overall amount of ice dumped into the sea
increased from 90 cubic km in 1996 to 224 cubic km in 2005.

Dr Rignot said that there are now signs that the more northerly glaciers of
Greenland are beginning to adopt the pattern of movements seen by those in
the south. "The southern half of Greenland is reacting to what we think is
climate warming. The northern half is waiting, but I don't think it's going
to take long," he said.

© 2006 Independent News and Media Limited