Greenland Ice Cap Is Melting, Raising Sea Level
By Paul Recer
The Associated Press
WASHINGTON (AP) - A warming climate is melting more than
50 billion tons of water a year from the Greenland ice sheet, adding to a
nine-inch global rise in sea level over the last century and increasing the
risk of coastal flooding around the world, a study shows.
A NASA high-tech aerial survey shows that more than 11
cubic miles of ice id disappearing from the Greenland ice sheet annually,
says the study appearing Friday in the journal of Science. That's
equal to about 1.25 trillion gallons and is enough to raise the sea level by
.13 millimeters a year.
"We see a significant trend (in loss of ice
mass)," said William B. Krabill, first author of the study.
"When we can go back after five years and see 10 meters of glacier
gone, there is something happening."
Krabill, a NASA scientist and head of the ice sheet
measurement project, said the melting of Greenland ice and the calving of
icebergs from Greenland glaciers is responsible for about 7 percent of the
annual rise in global sea level.
Over the last century, measurements suggest sea level has
risen about nine inches, enough to cause some low-lying areas that were once
high and dry to be awash at high tide or during storms. The
trend could get worse, said Krabill, if the Greenland ice sheet continues to
"The margins of the Greenland ice sheet are
undergoing significant thinning, in some places in excess of two meters a
year," said Krabill.
Just how much ice is disappearing from Greenland and
Antarctica, the world's largest reservoirs of ice, has long been uncertain.
The NASA survey is the first to give a comprehensive measurement of recent
changes in the Greenland ice sheet. Krabill said there is no similar
data for Antarctica.
Krabill said the study shows glaciers on Greenland are
moving more rapidly to the sea, caused, perhaps, by melting water that coats
the base of the glaciers and helps lubricate the downhill slide of the ice
"We are seeing widespread indications that something
like that is going on, causing the glaciers to move faster toward the
margins," said Krabill.
Krabill led a NASA team that used an aerial laser survey
technique to measure the level of ice on Greenland and compare that with
data from a similar survey five years ago. The technique involves a
laser that fires 5,000 bursts of light a second toward the surface from an
airplane flying over the ice. The light bounces back to a receiver on
the airplane, giving a measure of altitude. The airplane's location
and path is measured using the Global Positioning Satellite system.
The result is a precise measurement of altitude of the ice covering
Greenland. A survey five years ago used a similar technique.
A comparison of the two surveys found there had been
severely thinning along the southern and southeastern margins of the
Atlantic Ocean island, while there was a slight thickening of ice in the
western highlands. But the net effect, said Krabill, was a significant
loss of ice from the island.
"What we see happening in Greenland may be an
indication of the bigger picture," said Waleed Abdalati, another NASA
scientist and a co-author of the study. The Greenland ice sheet, he
said, is more sensitive to climate change than the ice in Antarctica because
Greenland has a more temperate climate.
The process of losing ice can itself speed up the
melting, said Abdalati.
"As ice melts, more solar energy is absorbed,
causing the surface to get warmer," accelerating the melt, he said.
"This is called a positive feed back."
Temperature measurements along Greenland's east coast
show a half degree rise over five years, said Abdalati. Measurements
elsewhere on the island show no change or even a slight cooling, he said.
Greenland contains about 8 percent of the Earth's
grounded ice. Antarctica, at the South Pole, holds about 91 percent.
Melting all the ice on Greenland - a very unlikely event
that would take thousands of years - could raise the world's sea level by
about 21 feet, said Abdalati. But long before that happens, a creeping
rise in sea level could displace millions of people who now live along the
"You would have major effects if the sea level goes
up" only a few inches, Abdalati said.
NASA is planning in 2001 to launch a satellite, called
IceSat, that will survey the major ice sheets in the world. The
satellite will orbit nearly directly over the poles, taking almost constant
measurements of the ice and determine how it is changing with tim