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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