In the British-led study by 68 experts, the scientists estimated that the Amazon forest had been absorbing two billion tonnes of carbon dioxide a year on average since the 1980s. It lost three billion tonnes in the 2005 drought, however, which killed trees and slowed forest growth.
“The total impact was an extra five billion tonnes of carbon dioxide in the atmosphere,” said the study leader, Oliver Phillips, a professor of tropical ecology at Leeds University in England. “The Amazon forest was surprisingly sensitive to drought,” he noted. Soft-wooded trees, including palms, were found to be particularly vulnerable.
Paradoxically, the forest’s accumulation of carbon before 2005 may have been aided by global warming, which improved plant growth. Phillips said the expansion of the Amazon’s carbon storage had helped slow global warming since the 1980s. “Just because we’ve been getting this subsidy doesn’t mean we can count on it for ever,” he said.
The United Nations climate panel projected in 2007 that rising temperatures may cause more drought and “lead to gradual replacement of tropical forest by savannah” in the eastern Amazon by the middle of this century. If the climate becomes drier, rain forests from Africa to Latin America may speed up global warming, scientists say.
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