Drought hits the Amazon – again.

In 2005, the Amazon basin experienced what at the time was called a ‘once in 100 year’ drought.  Changes in normal rainfall patterns were at the time attributed to unusually warm seas in the South Atlantic.  As a result of the drought, large areas of rainforest began to die back and as they did so, began to release carbon dioxide into the atmosphere.  The Amazon basin, one of the worlds great carbon sinks, became a carbon emitter.  In all it was calculated that five billion tonnes of carbon dioxide were released.

In 2010, it all happened again.  Two ‘once in 100-year’ events within 5 years prove nothing, yet it is cause for concern.  The 2010 event was more intense than the 2005 drought with rivers dropping to record low levels disrupting the life and economy of Amazonia.  Preliminary calculations indicate that the resultant dieback will release even more carbon dioxide than the 2005 drought – an amount equivalent to the annual release by the USA.  Some tree deaths will be a long-term result of the 2005 drought that left many weakened and unable to tolerate further drying.  By the same argument, the final impact of the 2010 drought will not be felt for several years, the climate over the next decade will determine the fate of trees weakened but not killed last year.

A joint team from Brazil’s Amazon Environmental Research Institute and the University of Leeds, which has just produced a report on the drought, is carrying out research into the impact of these droughts.  Dr Simon Lewis, from the University of Leeds, who co-authored the report with Dr Paulo Brando of AERI, said, “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.”

The Amazon rainforest is one of the world’s great carbon sinks covering an area approximately 25 times the size of the UK.  Scientists at Leeds have previously shown that in a normal year the forests absorb approximately 1.5 billion tonnes of CO2.  However, for 2010 – 11, they predict that Amazon forests will switch from a carbon sink to a net emitter, releasing more than 5 billion tonnes of carbon dioxide over the coming years.  In addition to this figure, there will be the release from the continuing logging operations and forest fires that may well be more frequent following the drought.  Suddenly the world has been joined by another USA.

Over the last three years the Southern hemispheres has seen a succession of extreme events.  The Brazilian droughts, the fires in Victoria, record floods in Queensland and the biggest tropical cyclone ever recorded in Australia.  The monsoons that caused the flooding in Pakistan were under the influence of the southern oceans.  None of this should surprise us.  The southern hemisphere is the blue hemisphere, dominated by its oceans and these extreme events are attributed to ‘abnormal’ warming of the oceans.  Climate is intimately tied to oceanic conditions; oceans are the heat store, exchanging energy with the atmosphere, so driving weather patterns.  In a warming world, it is the southern hemisphere that will experiences climatic changes first.  However, the world has one integrated climatic system – where the south leads, the north will follow.

[Mike Shipley.]

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