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For almost four decades, climate scientists have been extracting cores of ice from polar regions. From the chemistry of ancient ice, they have constructed theories about how these cold wastelands drive the world’s climate system. But 29 years ago, a lowly American graduate in coal geology decided that the high ice fields of the tropics might tell a different story. After 50 expeditions in the Himalayas, the Andes, East Africa and Tibet, Lonnie Thompson has probably spent more time at high altitude than any other researcher. And with thousands of metres of ice cores stored away in his deep…