Amazon drought may shift region from carbon sink to carbon emitter
Typically, the Amazon rainforest acts as a carbon sink, absorbing on average 1.5 billion metric tons of CO2 annually. Researchers in the UK and Brazil are now concerned that the role of, the Amazon may turn to an emitter of carbon emitter due to changing conditions in the region.
In 2005 the Amazon experienced a “once-in-a-century” drought, only to be hit yet again with an even more intense and widespred drought in 2010. The combined emissions from the two droughts have likely been enough to cancel out the carbon absorbed by the rainforest over the past ten years said the scientists, who released their report last week, published in the journal Science.
In addition to not absorbing CO2 in both 2010 and 2011, researchers estimate that a further 5 billion tons of CO2 will be emitted from the rainforest over the coming years once the trees killed last year rot – resulting in a net impact of 8 billion metric tons of released carbon. By comparison, the United States released 5.4 billion metric tons of carbon in 2009 from burning fossil fuels.
The full impact of the 2010 Amazon drought won’t be known until on-the-ground measurements are completed, says Dr. Paulo Brando of Brazil’s Amazon Environmental Research Institute
“It could be that many of the drought susceptible trees were killed off in 2005, which would reduce the number killed last year,” says Brando. “On the other hand, the first drought may have weakened a large number of trees so increasing the number dying in the 2010 dry season.
“Our results should be seen as an initial estimate. The emissions estimates do not include those from forest fires, which spread over extensive areas of the Amazon during hot and dry years. These fires release large amounts of carbon to the atmosphere.”
What remains an open and crucial question is whether these two droughts are driven by rising levels of greenhouse gases in the atmosphere, or if they are just “an anomaly,” says University of Leeds ecologist Simon Lewis, a lead author of the study. The pattern does fit projections from many climate models indicating more extreme weather events and intense droughts.
“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 Lewis.
The most extreme scenarios turn large swaths of rainforest into savannah by mid-century with reduced levels of plant and animal biodiversity.
“If drought events continue,” concludes the report, “the era of intact Amazon forest buffering the increase in atmospheric carbon may have passed.”
Image credit: visionshare, courtesy Flickr