Droughts could turn Amazon basin from greenhouse gas eater to source of gases

The widespread drought has raised concerns about the rainforest’s future as a major absorber of carbon emissions, the scientists said in a study released last week.

Frequent severe dry spells like the ones in 2005 and 2010 risk turning the Amazon from a greenhouse gas eater into a source of the gases, which could definitely accelerate global warming, the report said.

Since the droughts killed off many trees, the team predicts that the Amazon will not be able to absorb as much carbon dioxide as usual in the coming years. Even worse, rotting trees may release as much as 5 billion tons of CO2 into the atmosphere in the years to come, almost as much as the entire United States emitted from fossil fuel usage in 2009.

“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.

Lewis is the scientist who received an apology from the Sunday Times newspaper last year for their report on the so-called “AmazonGate” affair.

He said it is “difficult to detect patterns from just two observed droughts, but to have them close together is concerning.”

Both droughts were associated with abnormally warm seas in the Atlantic Ocean off the Brazilian coast. “If that turns out to be driven by escalating greenhouse gas concentrations in the atmosphere, it could imply that we'll see more drought years in the near future,” Lewis told BBC News.

“If events like this do happen more often, the Amazon rainforest would reach a point where it shifts from being a valuable carbon sink slowing climate change to a major source of greenhouse gases,” he said.

Scientists used data from a US/Japanese satellite -- Tropical Rainfall Measuring Mission (TRMM) -- that monitors rainfall along a belt that extends either side of the equator for their research.

Observation of data showed that the 2010 drought covered more than 1.8 million square miles, whereas the 2005 drought covered only 1.2 million square miles.

The Universities of Leeds, Sheffield and the Instituto de Pesquisa Ambiental da Amazonia (IPAM) in Brazil collaborated on the research. The work was funded by the Royal Society, Gordon and Betty Moore Foundation and the US National Science Foundation.

The paper entitled 'The 2010 Amazon Drought' by Simon L Lewis, Paulo M Brando, Oliver L Phillips, Geertje MF van der Heijden and Daniel Nepstad is published in the journal Science on Friday February 4, 2011.