The 2005 Amazon drought was unprecedented. It was thought to occur just once in a century. But last year was even worse, leading to massive biomass degradation and CO2 emissions. And yet another 2010 climate record.

A team of Brazilian and British researchers noticed last year’s drought affected a much larger portion of the Amazon basin, some 1.16 million square miles of rainforest, compared to 734,000 square miles in 2005. The 2010 drought had three epicenters where vegetation died off, whereas in 2005 the drought was focused on the southwestern part. The findings have been published in the latest edition of Science.

Although Earth’s biosphere is in theory more or less carbon neutral, serving as a permanent storage facility for thousands of gigatonnes of pure carbon and thereby keeping atmospheric levels both low and stable, some areas tend to act as net sinks.

On land these are mostly regions with high precipitation and stable and high moisture content in the organic soils. [It is important to note the natural sinks don’t really extract CO2 from the atmosphere, they feed the deeper, geological carbon cycle – that creates its own balance with the atmosphere by having equal areas subsiding (and allowing sedimentation) as areas rising again, where fossil carbon deposits are being eroded and carbon is released as CO2. What modern humans mostly do is interfering with this deep carbon cycle, speeding events up from a millions of years time scale, to centuries. Aren’t we dumb.]

The Amazon basin is an example of a net sink of CO2 – or so we had hoped. It used to store 1.5 billion tones of CO2 per year. In 2010, just as in 2005, this was put in reverse by a massive die-off of trees, making the region a net emitter of CO2, some 5 billion tonnes the researchers estimate, almost equivalent to US fossil fuels emissions.

From the atmospheric perspective the news is even worse, as the degradation process is slow and another 3 billion tonnes of CO2 are not being absorbed in 2010 and 2011, making the total amount of added CO2 of this single drought event 8 gigatonnes of CO2.

The problem is these droughts (long disruptions of the daily rain cycle are very rare in rainforests) are new to the ecosystem, possibly a positive feedback to climate change and further disturbing the balance. Lead author Simon Lewis, an ecologist at the University of Leeds, fears the Amazon rainforest could turn into a net emitter of CO2.

© Rolf Schuttenhelm | www.bitsofscience.org