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Earth is losing vast historical archives

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AMSTERDAM, Netherlands — With glaciers, coral and old-growth trees swiftly disappearing, scientists warn that the Earth is losing the vast historical archives stored within them.

These natural records are invaluable in tracing long term climatic changes, and sometimes reveal a graphic picture of human drama, researchers said in a series of papers and remarks at an international conference of scientists on global warming.

Samples drilled recently from a glacier in Tibet showed dust mapping a six-year drought in northern India that began in 1790, estimated to have killed 600,000 Indians, Raymond Bradley, director of the climate center of the University of Massachusetts, said recently.

Data collected from Indian Ocean coral reefs indicated that the collapse of the monsoon in those disastrous years was caused by el nio, a weather phenomena that occurs when trade winds and Pacific Ocean currents reverse directions, Bradley said.

But such records are vanishing as ancient forests fall under the ax, as mountain glaciers melt and recede, and as corals are bleached by warm sea water or damaged by coastal development.

"It's like burning down the museum," said Thomas F. Pedersen, of the University of British Colombia, Canada. "We have perhaps a few decades left."

Nearly all ice caps in the middle latitudes of Africa and South America have disappeared. The ice on Kilimanjaro in Tanzania, Africa's highest point and a popular tourist destination, has shrunk by 82 percent since 1912, according to a survey completed last year.

Two years ago, researcher Lonnie G. Thompson of Ohio State University planted a weather station in more than 3 feet of ice on Kilimanjaro, thinking it would stand for years. Ten months later it toppled over.

The conference also heard reports on new thinking about abrupt climate changes.

Studies in the early 1990s of Greenland's glaciers showed repeated patterns over the last half million years of sudden shifts in ocean currents, raising temperatures across the northern hemisphere by up to 50 degrees within a decade.

Although modern man has never witnessed such cataclysmic changes, the Greenland studies show "abrupt changes are the rule rather than the exception in climate history," said Stefan Rahmstorf, of the Potsdam Institute of Climatic Research.

He compared such changes to an airplane crash — low probability but high impact. And they become more likely to occur because of human activity, he said.