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But a temperature rise in recent years, measured at about a full degree since 2000, is eroding the 150-foot-high blocks of ice that gave Kilimanjaro its distinctive white cap.

"The ice will be gone by about 2020," said Thompson, the first author of a study appearing Friday in the journal Science.

Threatened Tourist Attraction

The diminishing ice already has reduced the amount of water in some Tanzanian rivers and the government fears that when Kilimanjaro is bald of snow tourists will stop coming.

"Kilimanjaro is the number one foreign currency earner for the government of Tanzania," Thompson said. "It has its own international airport and some 20,000 tourists every year. The question is how many will come if there are no ice fields on the mountain."

The mountain is enshrined in literature, most notably Ernest Hemingway's The Snows of Kilimanjaro and some ancient beliefs in Africa hold the mountain to be a sacred place.

Water from the mountain supplies villages and hospitals and already some are suffering, Thompson said.

Diminishing Cores Hold History

Scientists raced to drill cores from the shrinking ice field because the frozen layers tell a story of Africa's ancient weather, and, indirectly, give clues about the global climate.

An extremely wet period evidenced in the ice corings matches independent studies that showed about 11,000 years ago the lakes in Africa spilled across vast areas of the continent.

Lake Chad, for instance, said Thompson, grew until it covered 135,000 square miles, about the size of the present day Caspian Sea. The African lake now is only about 6,500 square miles.

That wet period ended and the ice corings show that Africa slid into a deep drought about 4,000 years ago.

This dry period is also found in other records, including some written history, Thompson said.

"This dry period appears in the historic record in Egypt," he said. "Writings on tombs talk about sand dunes moving across the Nile and people migrating. Some have called this the Earth's first dark age."

Africa was not alone in the global drought. Thompson said other records show that civilizations during this period collapsed in India, the Middle East and South America.

Fast Decline Visible

Researchers put markers atop the ice field blocks in 1962 and Thompson said measurements using satellites show the summit of the ice has been lowered by about 56 feet in 40 years.

The margin of the ice also has retreated more than six feet in the past two years, he said.

"That's more than two meter's worth of ice lost from a wall 50 meters [164 feet] high," Thompson said. "That's an enormous amount of ice."