The New York Times (pg. F1)  [Printer-friendly version]
January 8, 2008

IN GREENLAND, ICE AND INSTABILITY

By Andrew C. Revkin

The ancient frozen dome cloaking Greenland is so vast that pilots have
crashed into what they thought was a cloud bank spanning the horizon.
Flying over it, you can scarcely imagine that this ice could erode
fast enough to dangerously raise sea levels any time soon.

Along the flanks in spring and summer, however, the picture is very
different. For a lengthening string of warm years, a lacework of blue
lakes and rivulets of meltwater have been spreading ever higher on the
ice cap. The melting surface darkens, absorbing up to four times as
much energy from the sun as unmelted snow, which reflects sunlight.
Natural drainpipes called moulins carry water from the surface into
the depths, in some places reaching bedrock. The process slightly, but
measurably, lubricates and accelerates the grinding passage of ice
toward the sea.

Most important, many glaciologists say, is the breakup of huge
semisubmerged clots of ice where some large Greenland glaciers,
particularly along the west coast, squeeze through fjords as they meet
the warming ocean. As these passages have cleared, this has sharply
accelerated the flow of many of these creeping, corrugated, frozen
rivers.

All of these changes have many glaciologists "a little nervous these
days -- shell-shocked," said Ted Scambos, the lead scientist at the
National Snow and Ice Data Center in Boulder, Colo., and a veteran of
both Greenland and Antarctic studies.

Some fear that the rise in seas in a warming world could be much
greater than the upper estimate of about two feet in this century made
last year by the Intergovernmental Panel on Climate Change. (Seas rose
less than a foot in the 20th century.) The panel's assessment did not
include factors known to contribute to ice flows but not understood
well enough to estimate with confidence. All the panel could say was,
"Larger values cannot be excluded."

A scientific scramble is under way to clarify whether the erosion of
the world's most vulnerable ice sheets, in Greenland and West
Antarctica, can continue to accelerate. The effort involves field and
satellite analyses and sifting for clues from past warm periods,
including the last warm span between ice ages, which peaked about
125,000 years ago and had sea levels 12 to 16 feet higher than
today's.

The Arctic Council, representing countries with Arctic territory, has
commissioned a report on Greenland's ice trends, to be completed
before the 2009 round of climate-treaty talks in Copenhagen, at which
the world's nations have pledged to settle on a long-term plan for
limiting human-caused global warming.

Konrad Steffen, a University of Colorado glaciologist who has camped
on the shoulders of Greenland's ice sheet each year since 1990, is a
United States author working on that study. Last August, he and a team
focusing on the ways meltwater might affect ice movement dropped a
camera 330 feet down a water-filled moulin to explore whether the
plumbing system can be mapped.

Research on alpine glaciers shows that as more water flows through
such apertures, ice can shift more quickly. But eventually large
sewerlike conduits form, limiting the lubrication effect. The camera
drop was only an initial test.

Alberto Behar, a NASA engineer who designed the camera, said some
unconventional methods are being considered to chart the flow of such
water. "We had ideas to send rubber ducks down and see if they pop
out in the ocean," he said. "They'd have a little note saying,
'Please call this number if you find me."'

The changes seen in Greenland may turn out to be self-limiting in the
short run; surging glaciers can flatten out and slow, for instance. Or
they may be a sign that the island's ice -- holding about the same
volume of water as the Gulf of Mexico -- is poised for a rapid
discharge. Scientists are divided on that question, and also on
whether there is a near-term risk from a Texas-size portion of West
Antarctica's ice sheet that is also showing signs of instability. This
split divides those foreseeing a rise in the sea level of a couple of
feet this century from water added by Greenland, West Antarctica and
fast-vanishing mountain glaciers, and a few experts who speak of a
couple of yards in that time.

Those holding a more conservative view of Greenland's near-term fate
include Richard Alley of Pennsylvania State University, who noted that
ice cores and tests of organic material from beneath the ice imply
that the main core of the Greenland ice sheet clearly endured
thousands of years of warming in the past without vanishing.

"It's basically a big lump of ice sitting on this bedrock," Dr.
Alley said in describing Greenland's behavior in warm conditions.
"What it tries to do is snow more in the middle and melt more on the
edges. If it pulls its edges back, then there's less area to melt, and
that helps it survive. That's why you can have a stable ice sheet in a
warmer climate."

But there is no significant debate on the long-term picture any more:
Should greenhouse-gas emissions follow anything close to a "business
as usual" rise, the resulting warming and ice loss at both ends of
the earth would cause coasts to retreat for centuries to come. While
it was circumspect about near-term changes, the intergovernmental
panel was confident about that long view.

The prospect of having no "normal" coastline for the foreseeable
future has many scientists deeply concerned.

"What is at stake is the stability we have always taken for granted"
both for coasts and climate itself, said Jason E. Box, an associate
professor of geography at Ohio State University. Dr. Box presented
fresh findings at the American Geophysical Union meeting last month
showing that several Greenland glaciers accelerated sharply in direct
response to warming, both in a warm spell starting in the 1920s and
now.

Eric Rignot, a longtime student of ice sheets at both poles for NASA's
Jet Propulsion Laboratory, said he hoped that the public and
policymakers did not interpret the uncertainty in the 21st-century
forecast as reason for complacency on the need to limit risks by
cutting emissions.

Dr. Rignot recently proposed that unabated warming could result in
three feet of global sea rise just from water flowing off Greenland,
three feet from Antarctica and 18 inches as the remaining alpine
glaciers shrivel away.

This is similar to projections by the most prominent NASA climate
scientist, James E. Hansen, but more than twice the three-feet rise
that many glaciologists seem to agree on as an outer bound for what is
possible by the end of the century.

"It is too early to reassure that all will stabilize, and similarly
there is no way to predict a catastrophic collapse," Dr. Rignot said.
"But things are definitely far more serious than anyone would have
thought five years ago."