Sea levels likely to rise much faster than was predicted
By Steve connor, Science Editor in St Louis
Published: 17 February 2006
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.
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.
<http://red.as-eu.falkag.net/red?cmd=url&flg=0&&rdm=74606010&dlv=1028,30022,381090,177088,660284&kid=177088&ucl=111111A&dmn=.hornet.uea.ac.uk&scx=1024&scy=768&scc=32&sta=,,,1,,,,,,,0,9,0,6896,6893,6429,3555,0&iid=381090&bid=660284&dat=>
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