WASHINGTON, July 1 (UPI) — Global warming caused by human activity may not be a modern phenomenon because even prehistoric man may have affected his environment, researchers say.
Early hunters contributing to the extinction of wooly mammoths around 15,000 years ago may have contributed to a side effect of heating up the planet, an American Geophysical Union release said Wednesday.
In a study published in the AGU journal, researchers propose a scenario to explain how the ancient hunters could have triggered global warming.
In northern regions, mammoths would have grazed down birch trees, leaving only grasslands. As mammoth populations dropped because of human hunting, birch trees spread, dominating the grasses.
The trees would change the color of the landscape making it much darker, the study says, and absorbing more of the sun’s heat, in turn heating up the atmosphere.
Researchers examined ancient pollens preserved in Alaska, Siberia and the Yukon Territory. Around 15,000 years ago, they say, the amount of birch pollen started to rise quickly.
“With the extinction of this (wooly mammoth) keystone species, it would have some impact on the ecology and vegetation — and vegetation has a large impact on climate,” says lead study author Chris Doughty of the Carnegie Institution for Science in Stanford, Calif.
“A lot of people still think that people are unable to affect the climate even now, even when there are more than 6 billion people,” says Doughty. The new results, however, “show that even when we had populations … of magnitude smaller than we do now, we still had a big impact.”
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