Posted on 14-6-2002

Western Pollution Influences African Drought
By DARREN YOURK*, Globe and Mail, Thursday, June 13, 2002

Pollution from North America and Europe may have sparked severe droughts
that crippled countries south of the Sahara desert in the 1980s, new
research done in part by a Canadian scientist shows.

A report published in New Scientist magazine Thursday says climate modeling
studies by scientists in Canada and Australia points to clouds of sulphur,
soot, carbon, ammonium and nitrate spewed out by Western factories and
power plants as catalysts for the environmental crisis that plagued parts
of Africa. As these compounds travel through the atmosphere, they create
aerosols that influence cloud formation, altering the temperature of the
Earth's surface and leading to dramatic shifts in regional weather
patterns, the report
argues.

Ulrike Lohmann, a professor in the department of physics and atmospheric
science at Dalhousie University in Halifax and Leon Rotstayn of Australia's
Commonwealth Scientific and Industrial Research Organization created a
computer model that simulated the global climate and interactions between
clouds and sulphur dioxide emissions. "These aerosols are airborne
particles that reflect radiation from the sun back to space," Dr. Lohmann
told globeandmail.com. "Because of that, we receive less radiation at the
earth's surface, leading to cooling. "We do see this cooling over the whole
Northern Hemisphere. If you have a cooling in the North Atlantic that is
reducing the strength of the African monsoon. If you have a weaker monsoon,
the zone gets less precipitation. That's the chain of argument we are
trying to make." The researchers did two simulations, one that included the
huge sulphur emissions from the Northern Hemisphere during the 1980s and
one that did not.

In the past 30 to 40 years, the Sahel — a loosely defined band across
Africa, south of the Sahara and including parts of Ethiopia in the east and
Guinea in the west — has suffered the most severe and sustained drought
seen in any part of the world. During the worst years, between 1972 and
1975 and between 1984 and 1985, up to a million people starved to death as
a result. "We're saying that these conditions have to do with the cooler
North Atlantic, but the cooler North Atlantic is not part of a natural
variability," Dr. Lohmann said. "That is caused by man-made pollution in
North America and Europe."

In the researcher's model — similar to a weather forecasting model but run
over a much longer period of time — the Earth's surface in the north cooled
relative to the south when the man-made pollution was included, driving the
tropical rain belt south and causing droughts in the Sahel. "Evaluating the
difference in the two simulations allowed us to come to the conclusion that
we did," Dr. Lohmann said. "... That you would have a mid-latitude effect
that has far-reaching consequences in the tropics that surprised me at first."

Over the past few years, the droughts have become less severe, a change
that the researchers attribute to "clean-air" laws in North America and
Europe that reduced sulphur dioxide emissions in response to acid rain. The
full study will is due to be published soon in the Journal of Climate.