A widespread drought in the Amazon rain forest last year was worse than the "once-in-a-century" dry spell in 2005 and may have a bigger impact on global warming than the United States does in a year, British and Brazilian scientists said.
More frequent severe droughts like those in 2005 and 2010 risk turning the world's largest rain forest from a sponge that absorbs carbon emissions into a source of the gases, accelerating global warming, the report found.
Trees and other vegetation in the world's forests soak up heat-trapping carbon dioxide as they grow, helping cool the planet, but release it when they die and rot.
"If events like this happen more often, the Amazon rain forest would reach a point where it shifts from being a valuable carbon sink slowing climate change to a major source of greenhouse gases that could speed it up," said lead author Simon Lewis, an ecologist at the University of Leeds.
The study, published in the journal Science, found that last year's drought caused rainfall shortages over a 3 million square km expanse of the forest, compared with 1.9 million square km in the 2005 drought.
