Confirmation of climate change impact on polar ice sheets
2 March 2006
In the most comprehensive survey ever undertaken of the massive ice sheets covering
Greenland and Antarctica, NASA scientists confirm climate warming is changing how much
water remains locked in Earth's largest storehouses of ice and snow.
"If the trends continue and climate warming continues as predicted, the polar
ice sheets could change dramatically," said lead author Jay Zwally of NASA's Goddard
Space Flight Center. "The Greenland ice sheet could be facing an irreversible decline by the
end of the century."
This new survey is the first to inventory the losses of ice and the addition of new snow
on both in a consistent and comprehensive way throughout an entire decade.
There was a net loss of ice from the combined polar ice sheets between 1992 and 2002, and
a corresponding rise in sea level. The survey documented for the first time extensive thinning
of the West Antarctic ice shelves, an increase in snowfall in the interior of Greenland and
thinning at the edges. All are signs of a warming climate predicted by computer models.
Researchers used nine years of elevation mapping over much of Antarctica and 10.5 years of
data over Greenland from the European Remote-sensing Satellites. The survey pinpointed where
the ice sheets were thinning and where they were growing.
Greenland has large ice losses along the southeastern coast and a large increase in ice
thickness at higher elevations in the interior due to relatively high rates of snowfall. There
was a slight gain in the total mass of frozen water in the ice sheet over the decade studied,
contrary to previous assessments.
This situation may have changed in just the past few years. Last month NASA scientists at
the Jet Propulsion Laboratory reported a speed up of ice flow into the sea from several
"The melting of ice at the edges of the ice sheet is also increasing, which causes the ice
to flow faster," Zwally said. "A race is going on in Greenland between these competing forces
of snow build-up in the interior and ice loss on the edges. But we don't know how long they
will be approximately in balance with each other or if that balance has already tipped in
favor of the recently accelerating outflow from glaciers."
It is very different in Antarctica, where ice sheets had a major net loss of ice
due to outflow from West Antarctica. These losses, which may have been going on for decades,
outweighed the gains in snow and ice seen in the East Antarctic ice sheet and parts of
The ice shelves around West Antarctica are also thinning, with rising temperatures. The
floating ice shelves are vulnerable to climate change. Some ice shelves in the Antarctic
Peninsula have totally disintegrated in recent years, allowing the ice from the land to move
into the ocean faster.
Overall, the gains and losses of ice from the Greenland and Antarctic sheets, added up to
a net loss of ice to the sea. The Greenland ice sheet annually gained approximately 11 billion
tons of water, while Antarctica lost about 31 billion tons a year. The 20 billion net tons
added to the oceans is equivalent to the amount of fresh water annually used in homes,
businesses and farming in New York, New Jersey and Virginia.
"The contribution of the ice sheets to sea-level rise during the decade studied was smaller
than expected, just 2 percent of the recent increase of nearly 3mm (0.12 inches) a year,"
Zwally said. "Current estimates of the other major sources of sea-level rise - expansion of
the ocean by warming temperatures and runoff from low-latitude glaciers - do not make up the
difference, so we have a mystery on our hands as to where the water is coming from."