AMAZON FACES MORE DEADLY DROUGHTS

[Anonymous]

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.
Stranded
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
repeated.

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?
We
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

The
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.
“We
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.
“It
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
The
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.
“The
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.” 

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March 27, 2007 at 10:30 AM