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 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 say.
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 Holland.
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 said.
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
