February 8th, 2011 by Joshua S Hill
2005 saw the worst drought in the Amazon rainforest for over a hundred years, and was believed to be just that; a one in a hundred year event. Sadly, only five years later and another drought hit the Amazon rainforest.
And scientists now believe that the 2010 drought may have been even more devastating to the rainforest than its predecessor five years earlier.
Research published in the journal Science, also shows that the carbon impact of the 2010 drought may eventually exceed the 5 billion tonnes of CO2 that was released following the 2005 drought. As a drought ravages a forest, the trees eventually die off, not being able to find enough water to survive. As they die, the forests ability to draw in CO2 diminishes and the trees themselves rot and release what CO2 they had collected out into the atmosphere once again.
“Having two events of this magnitude in such close succession is extremely unusual, but is unfortunately consistent with those climate models that project a grim future for Amazonia,
said lead author Dr Simon Lewis, from the University of Leeds.
In 2005 the region was struck by a drought which killed trees, in a forest that covers an area approximately 25 times the size of the United Kingdom. A forest like this normally takes in about 1.5 billion tonnes of CO2 a year, counterbalancing the emissions from deforestation, logging and fire across the Amazon.
However, monitoring on the ground during the drought found that the forests in the Amazon had stopped absorbing CO2 and were releasing more as they died.
The researchers predict that the forests in the Amazon region will not absorb their usual 1.5 billion tonnes of CO2 during 2010 or 2011, and they fear that a further 5 billion tonnes of CO2 will be released into the atmosphere over the coming years once the trees that are killed by the 2010 drought start to rot.
“We will not know exactly how many trees were killed until we can complete forest measurements on the ground,” said Dr Paulo Brando, from Brazil’s Amazon Environmental Research Institute (IPAM). “It could be that many of the drought susceptible trees were killed off in 2005, which would reduce the number killed last year. 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.”
Some global climate models predict that droughts like the two that have hit the Aazon will become more frequent in a future that warms from greenhouse gas emissions.
“Two unusual and extreme droughts occurring within a decade may largely offset the carbon absorbed by intact Amazon forests during that time,” added Dr Lewis. “If events like this 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 gasses that could speed it up.”
“Considerable uncertainty remains surrounding the impacts of climate change on the Amazon. This new research adds to a body of evidence suggesting that severe droughts will become more frequent leading to important consequences for Amazonian forests.”
“If greenhouse gas emissions contribute to Amazon droughts that in turn cause forests to release carbon, this feedback loop would be extremely concerning. Put more starkly, current emissions pathways risk playing Russian roulette with the world’s largest rainforest.”
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