Greenland's ice cap is melting at a frighteningly fast rate
Chunks of ice regularly fall into the sea in Greenland, where ice is melting at a rate three times faster than it was only five years ago. (Science photo by J.A. Dowdeswell)
The vast ice cap that covers Greenland nearly three miles thick is
melting faster than ever before on record, and the pace is speeding year by
year, according to global climate watchers gathering data from twin satellites
that probe the effects of warming on the huge northern island.
The consequence is already evident in a small but ominous rise in sea
levels around the world, a pace that is also accelerating, the scientists say.
According to the scientists' data, Greenland's ice is melting at a rate three
times faster than it was only five years ago. The estimate of the melting trend
that has been observed for nearly a decade comes from a University of Texas
team monitoring a satellite mission that measures changes in the Earth's gravity
over the entire Greenland ice cap as the ice melts and the water flows down
into the Arctic ocean.
"We have only been watching the ice cap melt during a relatively short
period," physicist Jianli Chen said Thursday, "but we are seeing the
strongest evidence of it yet, and in the near future the pace of melting will
accelerate even more."
The same satellites tracking Greenland's ice cap also are monitoring the melt
rate of Antarctica's ice cover, and there too the melting is adding to the global
rise in sea level, according to another team of scientists.
Next to Antarctica, Greenland, a self-governing Danish territory, is the largest
reservoir of fresh water on Earth and holds about 10 percent of the world's
supply. The increasing flow of fresh water -- most of it from glaciers melting
on Greenland's eastern coast -- is already beginning to change the composition
of the ocean's salt water currents flowing past Northwestern Europe, the scientists
The result could be a critical change in the composition of the main ocean
current that flows past Europe's northern edge, blocking off warmer waters that
normally flow there and -- ironically -- making Northern Europe's weather colder
than normal, at least temporarily, while the rest of the globe continues warming.
The report on Greenland is being published today in the on-line edition of
the journal Science by the University of Texas scientists at Austin, including
Chen, aerospace engineer Byron Tapley and geologist Clark Wilson.
According to the researchers, surface melting of Greenland's ice cap reached
57 cubic miles a year between April of 2002 and November of 2005, compared to
about 19 cubic miles a year between 1997 and 2003.
"The sobering thing is to see that the whole process of glacial melting
is stepping up much more rapidly than before," said Tapley in a statement.
If the Greenland ice cap ever melted completely -- a highly unlikely event,
at least in the foreseeable future -- the scientists estimate it would raise
world's sea level by an average of 6.5 meters, or about 21 feet, more than enough
to drown all the world's low-lying islands and even some entire nations, like
The possibility of future sea level rises becomes even more evident when Antarctica's
huge ice sheets are considered.
Only last March two University of Colorado physicists used the same satellite
system to measure melting of ice on the Antarctic continent. Although earlier
evidence using other techniques appeared to show that the East Antarctica ice
sheet was actually thickening, satellite data gathered by Isabella Velicogna
and John Wahr at Boulder found that melting -- primarily from the West Antarctic
Ice Sheet -- had turned at least 36 cubic miles of ice to fresh water each year
from 2002 to 2005.
A recent report from the Intergovernmental Panel on Climate Change -- known
as the IPCC -- estimated that during all of the past century worldwide melting
ice from global warming had raised sea levels by only two-tenths of a millimeter
a year, or about 20 inches for the entire century.
But, according to Chen and his Texas team, the melting of Greenland's ice cap
is already raising global sea levels by six-tenths of a millimeter each year,
and the Colorado group estimates that melting of the West Antarctic Ice Sheet
alone is adding up to four-tenths of a millimeter of fresh water to sea levels
each year. In other words, the global sea level, due to melting of the ice in
Greenland and Antarctica combined, is already rising 10 times faster than the
IPPC's tentative estimates, the two analyses indicate.
Both the Texas and Colorado groups have been obtaining their data from two
satellites known as GRACE, the Gravity Recovery and Climate Experiment, which
fly in orbit 137 miles apart and determine with extraordinary accuracy just
how the mass of even small regions of the Earth change as ice melts and flows
away from the land to the sea.
The GRACE satellite mission is due to end next year, but the Texas team is
awaiting NASA approval for a new and improved satellite system to continue the
work, using laser beams rather than microwaves to measure ice cap melting, Chen
In a recent summary of the ice cap melting problem and its effect on sea levels
reported by Richard Kerr in Science, geoscientist Michael Oppenheimer of Princeton
said, "The time scale for future loss of most of an ice sheet may not be
millennia," as glacier models have suggested, "but centuries."
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