Amazon carbon sink threatened by drought(n botanist and co-author Abel Monteagudo...)

The Amazon accounts for more than half of the world's rainforest, covering an area 25 times as great as the United Kingdom. No other ecosystem on Earth is home to so many species nor exerts such control on the carbon cycle.

The study involved 68 scientists from 13 countries working in RAINFOR, a unique research network dedicated to monitoring the Amazonian forests.

To calculate changes in carbon storage they examined more than 100 forest plots across the Amazon's 600 million hectares, identified and measured over 100,000 trees, and recorded tree deaths as well as new trees. Weather patterns were also carefully measured and mapped.

In the wake of the 2005 drought the RAINFOR team took advantage of this huge natural experiment, and focused their measurements to assess how the drought had affected the forest.

The study found that for at least 25 years the Amazon forest acted as a vast carbon sink. A similar process has also been occurring in Africa.

In fact, over recent decades the tropical forests have absorbed one fifth of global fossil fuel emissions.

But in 2005 this process was reversed. Tree death accelerated most where drought was strongest, and locations subject even to mild drying were affected. Because of the study, we now know the precise sensitivity of the Amazon to warming and drought.

If repeated, Amazon droughts will accelerate climate warming and make future droughts even more damaging.

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