Can The Amazon Emit more Greenhouse Gases than the US?

A severe drought in the Amazon rain forest last year was worse than the "once-in-a-century" dry spell in which damaged the forest 2005 and may ultimately have a bigger impact on global warming than the United States does in a year, British and Brazilian scientists said on Thursday.

Simply put, trees and other vegetation in the world's forests soak up heat-trapping carbon dioxide as they grow, which helps to cool the planet, but they greenhouse gases 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 1.16 million square-mile (3 million square km) expanse of the forest, an increase of 50% of the square miles that were affected in the 2005 drought.

The drought was also more intense, killing more trees while having three major epicenters, whereas the 2005 drought was mainly focused in the southwester
Amazon.

As a result, the study predicted the Amazon forest will reverse its role as a carbon “sponge” and become an emitter of carbon gases. Instead of absorbing its usual 1.5 billion metric tons of carbon dioxide from the atmosphere in both 2010 and 2011, the affected areas will release 5 billion metric tons of the gas in the coming years, for a total impact of 8 billion metric tons. The combined emissions caused by the two droughts will probably be enough to cancel out the carbon absorbed by the forest over the past 10 years. In comparison, the United States emitted 5.4 billion metric tons of carbon dioxide from fossil fuel use in 2009.

The widespread drought last year dried up major rivers in the Amazon and isolated thousands of people who depend on boat transportation, to the surprise of climate scientists who had billed the 2005 drought as a once-in-a-century event.

The two droughts fit into predictive models developed by some climate models that call for the Amazon forest to face greater weather extremes this century, with more intense droughts making it more vulnerable to fires, which in turn could damage its ability to recover.

Under the most extreme scenarios in these models, large areas of the Amazon of the forest could evolve into an African savannah-like ecosystem by the middle of the century with much lower levels of animal and plant biodiversity.