Fri, Jul 16, 2010 - Page 7 News List

Mammoth hunters helped warm up northern latitudes, researchers say


Ancient hunters who stalked the world’s last woolly mammoths likely helped warm the Earth’s far northern latitudes thousands of years before humans began burning fossil fuels, according to a study of prehistoric climate change.

The demise of the leaf-chomping woolly mammoths contributed to a proliferation of dwarf birch trees in and around the Arctic, darkening a largely barren, reflective landscape and accelerating a rise in temperatures across the polar north, researchers at the Carnegie Institution for Science concluded.

The northward march of vegetation affected the climate because of the “albedo effect,” in which replacement of white snow and ice with darker land surfaces absorbs more sunlight and creates a self-repeating warming cycle, the study found.

The end of the last Ice Age, marked by a rise in temperatures worldwide and the dramatic retreat of glaciers that once covered much of the Northern Hemisphere, was already under way when the extinction of woolly mammoths began.

But the latest findings, scheduled to be published in the Geophysical Research Letters journal, suggest human activity played a role in altering Earth’s climate long before mankind began burning coal and oil for energy, though the effects of prehistoric hunting were minute by comparison.

If mammoth hunters helped hasten Arctic warming, that would potentially be the first such human impact on climate, preceding that caused by ancient farmers, Chris Field, director of the Carnegie Institution’s Department of Global Ecology and a coauthor of the study, said on Tuesday.

With the advent of agriculture about 7,000 years ago at more southern latitudes, humans are believed to have modified the climate through deforestation and cultivation of new plants, he said.

The research attributes about a fourth of the Arctic’s vegetation-driven warming to the decline of the woolly mammoth.

If human hunters helped kill off the large mammals, they bear some responsibility for warming the climate, the scientists said.

“We’re not saying this was a big effect,” Field said. “The point of the paper isn’t that this is a big effect. But it’s a human effect.”

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