[Dialogue] Climate change 'will dry Africa'

[Harry Wainwright]

Colleagues, more food for thought. Peace, Harry 
  _____  


BBC NEWS

Climate change 'will dry Africa' 

By Richard Black 

 

Environment Correspondent, BBC News website 

 

   Our model predicts an extremely dry Sahel in the future 
Isaac Held, Noaa 

 

Two new studies predict that climate change will make dry regions of Africa
drier still in the near future. 

Computer models of the global climate show the Sahel region and southern
Africa drying substantially over the course of this century. 

Sahel rainfall declined sharply in the late 20th Century, with droughts
responsible for several million deaths. 

The research comes just after the latest United Nations summit on climate
change opened in Montreal. 

"Our model predicts an extremely dry Sahel in the future," said Dr Isaac
Held of the US National Oceanic and Atmospheric Administration (Noaa), whose
team publishes its research in the scientific journal Proceedings of the
National Academy of Sciences (PNAS). 

"If we compare it against the drought in the 1970s and 80s, the late 21st
Century looks even drier - a 30% reduction in rainfall from the average for
the last century," he told the BBC News website. 

Sahel rainfall fell dramatically in the second half of the 20th Century;
since 1970, about half of the region has been in severe drought. 

In the late 1980s, a recovery began, but rainfall is not back to pre-1970
levels. 

Southern Africa has fared better than the Sahel, but research by another
Noaa group led by Marty Hoerling also projects a drier future for this
region. 

"Between 1950 and 1999, there has been about a 20% decline in summer
rainfall over southern Africa," he told the BBC News website. 

"Our modelling indicates much more substantial ongoing drying, with the
epicentre for drought in Africa effectively moving further south." 

Dr Hoerling's study has been submitted to the Journal of Climate for
publication. 

Getting physical 

This latest research may help pin down the physical processes which
determine African rainfall. 

"What we do know from observations is that if you have a warm north Atlantic
and a cool south Atlantic you'll get increased Sahel rainfall, and vice
versa," said Professor Chris Folland from the UK Meteorological Office. 

"But even temperatures in the Mediterranean sea can affect it as well." 

   No model has ever been run of an atmosphere with increased greenhouse gas
concentrations that hasn't produced a warming 
Chris Folland, UK Met Office 

 

The theory is that if the North Atlantic warms more than waters further
south, the rain belt is pulled north over the Sahel; if the southern waters
warm more, rain retreats south again, leaving the Sahel dry. 

The key to southern African rainfall, meanwhile, may be temperatures in the
Indian Ocean, according to Marty Hoerling's results. 

Rising concentrations of greenhouse gases in the atmosphere are projected to
increase temperatures in the Indian Ocean and the differential between
temperatures in the north and south Atlantic. 

Super models 

Projecting future climate change is far from an exact science, and other
computer models of African regions have come up with different results. 

But these latest results demonstrate how severe the impacts of human-induced
global warming may be for some of the poorest countries on the planet. 

The fact that their predictions contrast with other models of the same
regions also indicate the problems which policymakers face in trying to
adapt to the local consequences of global climate change. 

Scientists attempt to validate the various models by seeing how well they
simulate the climate of the recent past - the climate we know - when all the
key data is fed in. 

"Our simulation of the 20th Century is closer to what was observed in Africa
than other models," said Isaac Held. 

"That's why we're giving this model credence, though it's not enough to be
certain." 

The key, according to Chris Folland, is to develop better models which can
tie local details into global simulations; but he fully rejects the
conclusion drawn by some climate change sceptics that models are so
unreliable as to be next to useless. 

"No model has ever been run of an atmosphere with increased greenhouse gas
concentrations that hasn't produced a warming," he said. 

"They produce different amounts of warming, but they do all produce warming
and that's a universal result." 

Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4479640.stm

Published: 2005/11/29 22:37:03 GMT

C BBC MMV

 

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