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 user 2005-12-02 at 10:59:00 am Views: 71
  • #12990

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

    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.

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

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

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

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

    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.

    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.”
    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.

    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.”