The vast expanses of rainforest that make up the Amazon Basin have been called the lungs of the planet, as they breathe in carbon dioxide and release oxygen. Now, findings from biweekly airplane flights over the jungle show how a severe drought choked these lungs, constricting the uptake of carbon dioxide, a greenhouse gas. Worse, fires released tremendous amounts of carbon into the atmosphere, exacerbating global warming. The measurements started in 2010, during a drought year, and showed that the Amazon overall released 480 million metric tons of carbon into the atmosphere, the team reports today in Nature. (Slightly more went up in smoke, but the difference was taken up by the vegetation.) The next year was wet. The plants stored 250 million tons of carbon, just about compensating for the carbon released by forest fires. Scientists are concerned that climate change—with rising temperatures and more droughts—will reduce the rainforest’s storage of carbon and in turn hinder its ability to slow the pace of global warming.

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