May 25, 2006
Subtropic warming could mean bigger deserts: study
By Deborah Zabarenko
WASHINGTON (Reuters) - Earth's atmosphere is warming faster
over the subtropics than anywhere else, which could mean bigger
deserts and more drought from Africa to Australia to the Middle
East, researchers said on Thursday.
north and south latitude, crossing the southern United States,
southern China and north Africa in the Northern Hemisphere, and
southern Australia, South Africa and southern South America in
the Southern Hemisphere.
Based on 25 years of satellite data, researchers at the
University of Washington also determined that the jet streams
-- a pattern of westerly winds that help drive weather in both
hemispheres -- have shifted about 70 miles toward their
This is important because the jet streams mark the northern
and southern boundaries of the tropic climate zones, said John
Wallace, an atmospheric scientist and co-author of a research
paper in this week's Science journal. The jet streams' shift
toward the poles means the zones are expanding.
The research is not predictive, but does show a long-term
trend, Wallace said by telephone.
"If (this jet-stream shift) is going to stop and it just
ends up being 70 miles, that's not a big deal," he said. "But
if it were to continue at the same rate over the next century,
then that would amount to a couple of hundred miles
(kilometers) and that would start to have significant effects."
ENCROACHING ON THE TEMPERATE ZONE
The dry subtropical climate regions, which contain some of
the world's major deserts, could encroach into temperate
regions, Wallace said. Areas such as the Mediterranean,
southern Europe and the northern part of the Middle East could
have a tendency toward more drought, Wallace said.
The same might happen in southern Australia and South
Africa, he said.
The study does not address whether this warming is due to
the greenhouse effect or some other factor. It is different
from previous models, which saw the fastest warming in the
tropics, rather than the subtropics.
The greenhouse effect is seen as a major cause for global
warming, in which so-called greenhouse gases, especially carbon
dioxide, swaddle the Earth like a blanket, keeping the sun's
Some greenhouse warming is natural, but many scientists
believe that accelerated warming over the last century was
caused by human activities including coal-burning power plants
and the use of other fossil fuels.
Faster subtropical warming in the lower atmosphere, which
moves the jet streams, could push storm tracks toward the
poles, possibly reducing winter precipitation in places like
southern Europe, including the Alps, and southern Australia,
the scientists said in a statement.