NYT
February 19, 2001
Glacier Loss Seen as Clear Sign of Human Role in Global Warming
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.
Ohio State University
The glacier Qori Kalis in the Peruvian
Andes, pictured at top in 1983 and at
bottom in 2000. The melting rate of the
glacier has increased in the last 25 years,
scientists say, and since 1998 has vastly
accelerated.
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.
