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Amazon Drought Caused Huge Carbon Emissions

Posted by Lindy on February 4, 2011


http://planetark.org/wen/61097

A widespread drought in the Amazon rain forest last year was worse than the “once-in-a-century” dry spell in 2005 and may have a bigger impact on global warming than the United States does in a year, scientists said on Thursday. More frequent severe droughts like those in 2005 and 2010 risk turning the world’s largest rain forest from a sponge that absorbs carbon emissions into a source of the gases, accelerating global warming, the report found.

Trees and other vegetation in the world’s forests soak up heat-trapping carbon dioxide as they grow, helping cool the planet, but release it 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.

Last year’s drought caused rainfall shortages over a 3 million square km expanse of the forest, compared with 1.9 million square km in the 2005 drought. It was also more intense, causing higher tree mortality and having three major epicentres, whereas the 2005 drought was mainly focused in the south-western Amazon.

As a result, the study predicted the Amazon forest would not absorb its usual 1.5 billion metric tons of carbon dioxide from the atmosphere in both 2010 and 2011. In addition, the dead and dying trees would release 5 billion metric tons of the gas in the coming years, making a total impact of about 8 billion metric tons. The combined emissions caused by the two droughts were probably enough to have cancelled out the carbon absorbed by the forest over the past 10 years.

GREATER WEATHER EXTREMES

The widespread drought last year dried up major rivers in the Amazon and isolated thousands of people who depend on boat transportation, shocking climate scientists who had billed the 2005 drought as a once-in-a-century event. The two intense dry spells fit predictions by some climate models that the forest will 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. As a result, large parts of the forest could turn into a savannah-like ecosystem by the middle of the century with much lower levels of animal and plant biodiversity. Although human-caused deforestation in Brazil has fallen sharply in recent years, the forest is still vulnerable.

The crucial question is: Is this an anomaly or is it driven by climate change? If it is the latter, possibly by mid-century the Amazon rainforest as we know it will be no more.

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