Glacier Loss Seen as Clear Sign of Human Role in Global Warming
from the New York Times
February 19, 2001
By ANDREW C. REVKIN
The icecap atop Mount Kilimanjaro, which for thousands of years has
floated like a cool beacon over the shimmering plain of Tanzania,
is retreating at such a pace that it will disappear in less than 15
years, according to new studies.
The vanishing of the seemingly perpetual snows of Kilimanjaro that
inspired Ernest Hemingway, echoed by similar trends on ice-capped
peaks from Peru to Tibet, is one of the clearest signs that a
global warming trend in the last 50 years may have exceeded typical
climate shifts and is at least partly caused by gases released by
human activities, a variety of scientists say.
Measurements taken over the last year on Kilimanjaro show that its
glaciers are not only retreating but also rapidly thinning, with
one spot having lost a yard of thickness since last February, said
Dr. Lonnie G. Thompson, a senior research scientist at the Byrd
Polar Research Center of Ohio State University.
Altogether, he said, the mountain has lost 82 percent of the
icecap it had when it was first carefully surveyed, in 1912.
Given that the retreat started a century ago, Dr. Thompson said,
it is likely that some natural changes were affecting the glacier
before it felt any effect from the large, recent rise in carbon
dioxide and other heat- trapping greenhouse gases from smokestacks
and tailpipes. And, he noted, glaciers have grown and retreated in
pulses for tens of thousands of years.
But the pace of change measured now goes beyond anything in recent
centuries.
"There may be a natural part of it, but there's something else
being superimposed on top of it," Dr. Thompson said. "And it
matches so many other lines of evidence of warming. Whether you're
talking about bore- hole temperatures, shrinking Arctic sea ice, or
glaciers, they're telling the same story."
Dr. Thompson presented the fresh data yesterday at the annual
meeting of the American Association for the Advancement of Science
in San Francisco.
Other recent reports of changes under way in the natural world,
like gaps in sea ice at the North Pole or shifts in animal
populations, can still be ascribed to other factors, many
scientists say, but many add that having such a rapid erosion of
glaciers in so many places is harder to explain except by global
warming.
The retreat of mountain glaciers has been seen from Montana to
Mount Everest to the Swiss Alps. In the Alps, scientists have
estimated that by 2025 glaciers will have lost 90 percent of the
volume of ice that was there a century ago. (Only Scandinavia seems
to be bucking the trend, apparently because shifting storm tracks
in Europe are dumping more snow there.)
But the melting is generally quickest in and near the tropics, Dr.
Thompson said, with some ancient glaciers in the Andes - and the
ice on Kilimanjaro - melting fastest of all.
Separate studies of air temperature in the tropics, made using
high- flying balloons, have shown a steady rise of about 15 feet a
year in the altitude at which air routinely stays below the
freezing point. Dr. Thompson said that other changes could also be
contributing to the glacial shrinkage, but the rising warm zone is
probably the biggest influence.
Trying to stay ahead of the widespread melting, Dr. Thompson and a
team of scientists have been hurriedly traveling around the tropics
to extract cores of ice from a variety of glaciers containing a
record of thousands of years of climate shifts. The data may help
predict future trends.
The four-inch-thick ice cylinders are being stored in a
deep-frozen archive at Ohio State, he said, so that as new
technologies are developed for reading chemical clues in bubbles
and water in ancient ice, there will still be something to examine.
The sad fact, he said, is that in a matter of years, anyone
wanting to study the glaciers of Africa or Peru will probably have
to travel to Columbus, Ohio, to do so.
Dr. Richard B. Alley, a professor of geosciences at Pennsylvania
State University, said the melting trend and the link - at least
partly - to human influence is "depressing," not only because of
the loss of data but also because of the remarkable changes under
way to such familiar landscapes.
"What is a snowcap worth to us?" he said. "I don't know about you,
but I like the snows of Kilimanjaro."
The accelerating loss of mountain glaciers is also described in a
scientific report on the impact of global warming, which is being
released today in Geneva by the Intergovernmental Panel on Climate
Change, an influential network of scientists advising world
governments under the auspices of the United Nations. The melting
is likely to threaten water supplies in places like Peru and Nepal,
the report says, and could also lead to devastating flash floods.
Kilimanjaro, the highest point in Africa, may provide the most
vivid image of the change in glaciers, but, Dr. Thompson said, the
rate of retreat is far faster along the spine of the Andes, and the
consequences more significant. For 25 years, he has been tracking a
particular Peruvian glacier, Qori Kalis, where the pace of
shrinkage has accelerated enormously just in the last three years.
From 1998 to 2000, the glacier pulled back 508 feet a year, he
said. "That's 33 times faster than the rate in the first
measurement period," he said, referring to a study from 1963 to
1978.
In the short run, this means the hydroelectric dams and reservoirs
downstream will be flush with water, he said, but in the long run
the source will run dry.
"The whole country right now, for its hydropower, is cashing in on
a bank account that was built up over thousands of years but isn't
being replenished," he said.
Once that is gone, he added, chances are that the communities will
have to turn to oil or coal for power, adding even more greenhouse
gases to the air.
The changes in the character of Kilimanjaro are registering beyond
the ranks of climate scientists. People in the tourism business
around the mountain and surrounding national park are worried that
visitors will no longer be drawn to the peak once it has lost its
glimmering cap.
Dr. Douglas R. Hardy, a geologist at the University of
Massachusetts, returned from Kilimanjaro last Thursday with the
first yearlong record of weather data collected by a probe placed
near the summit.
Just before he left, he had a long conversation with the chief
ranger of Kilimanjaro National Park, who expressed deep concern
about the trend. "That mountain is the most mystical, magical draw
to people's imagination," Dr. Hardy said. "Once the ice disappears,
it's going to be a very different place."
And the melting continues. When Dr. Hardy climbed the mountain to
retrieve the data, he discovered that the weather instruments,
erected on a tall pole, had fallen over because the ice around the
base was gone.
http://www.nytimes.com/2001/02/19/science/19MELT.html?ex=991336312&ei=1&en=552fceb2ce4c4da8
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