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 user 2007-03-27 at 10:30:00 am Views: 63
  • #17439

    Amazon ‘faces more deadly droughts’
    Two years ago the world was shocked by pictures of hundreds of rotting fish floating in the world’s second largest river.
    villagers stared in bewilderment at dried out banks, and helicopters
    delivered food and water to isolated river communities.They were the
    images of the widespread drought in 2005 in the Amazon – an area of
    lush rainforest in most people’s imagination. It was the worst in some
    areas since records began, and prompted the Brazilian government to
    declare a state of emergency.Nearly two years on, the world may have
    forgotten the drought, but the scientific community has not. Meeting at
    Oxford University this week, many of the world’s leading experts on
    climate change and Amazonia have been grappling with issues critical to
    the future climate of the world.Did global warming cause the drought?
    How likely is it that such droughts will be repeated in a warming
    world? And just how much devastation did the drought cause?There was
    broad consensus that the 2005 drought was linked not to El Nino – the
    periodic phenomenon which begins with a warming of waters in the
    Pacific – as with most previous droughts in the Amazon, but to warming
    sea surface temperatures in the tropical North Atlantic.Peter Cox,
    professor in climate change dynamics at the University of Essex in the
    UK, thinks the same factors which caused the drought are likely to be

    What drives it, he says, is the warming of the North
    Atlantic Ocean in the Tropics relative to the South – this causes less
    rain to fall
    Forest dieback’

    So how often could such droughts happen?
    can’t say for sure that any individual drought is caused by global
    warming – but we can say the probability of such an event will increase
    as a result of human-induced climate change Professor Peter Cox

    Hadley Centre climate change model predicts that, under current levels
    of greenhouse gas emissions, the chances of such a drought would rise
    from 5% now (one every 20 years) to 50% by 2030, and to 90% by 2100.
    can’t say for sure that any individual drought such as the one in 2005
    is caused by global warming,” says Mr Cox.”But we can say the
    probability of such an event will increase as a result of human-induced
    climate change and could be very common indeed by the end of the
    century.”The Hadley Centre model is one of several global climate
    models (GCMs) attempting to predict weather changes in the Amazon.It is
    best known for warning of catastrophic losses of forest in the Amazon
    over a period of decades known as “forest dieback”.Other models show
    very different patterns of rainfall over the Amazon, but experts at the
    conference regard the Hadley model as one of the more robust.”The
    Hadley Centre model does a credible job,” says Carlos Nobre, the
    Brazilian chair of the International Geosphere-Biosphere
    programme.”What all the GCMs predict is much greater variability in the
    weather, and the Hadley model captures that well.”

    Human factor?
    There is less uncertainty about the impact and the unusual nature of the 2005 drought.
    was very atypical in its location and intensity,” says Mr Nobre.”Most
    Amazonian droughts occur in the north-eastern Amazon, but this one
    started in the west and south-west, and its impact spread as far as the
    centre and east.”Downstream in the city of Manaus, the Amazon’s level
    dropped three metres lower than averageMany communities dependent on
    the river for transport were left stranded as tributaries dried out.
    For the first time, a very large spread of forest fires was recorded in
    the south-west region.New research by Luiz Aragao at Oxford
    University’s Environmental Change Institute shows the extent of the
    fires.”An area of 2,800 sq km (1081 sq miles) was lost due to an
    extensive leakage of fires into newly-flammable forest,” he says.That
    is an area more than 1.5 times the size of Greater London.Mr Aragao’s
    research shows the fires occurred mainly where there was human activity
    which could ignite them.In other areas affected by the drought where
    there are few humans, such as south-eastern Peru, there was little
    evidence of any fires.

    High impact
    more alarming predictions for the Amazon say the combination of forest
    fires, drought, deforestation, changes in land use (such as soya
    production) and global warming will combine to push the Amazon over a
    “tipping point” into a cycle of destruction.
    However low the
    probability, changes to the Amazon are likely to be a ‘high impact’
    event on the world’s climate.Scientists at the conference were keen to
    stress they do not know the risk of this occurring, but talked instead
    of “corridors of probability”.

    There is disagreement over these corridors.
    Hadley Centre model predicts it is very likely indeed that the Amazon
    will be severely impacted by climate change over the next few decades,”
    says Professor Cox.”But if you take all the models, then maybe a 10 to
    40% probability is more defensible.”But however low the probability,
    changes to the Amazon are likely to be a “high impact” event on the
    world’s climate.As one conference speaker pointed out: “You wouldn’t
    get on a plane if you knew there was a 10% chance of it crashing.”