African droughts triggered by Western pollution

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African droughts " triggered by Western pollution "

 

June 02

 

Exclusive from New Scientist

 

Emissions spewed out by power stations and factories in North America

and Europe may have sparked the severe droughts that have afflicted

the Sahel region of Africa. The droughts have been among the worst

the world has ever seen, and led to the infamous famines that

crippled countries such as Ethiopia in the 1980s.

 

Sahel dries out

 

The cause appears to be the clouds of sulphur belched out

alongside the soot, organic carbon, ammonium and nitrate produced

when fossil fuels are burnt, according to researchers in Australia

and Canada. As these compounds move through the atmosphere, they

create aerosols

that affect cloud formation, altering the temperature of the Earth's

surface and leading to dramatic shifts in regional weather patterns.

 

In the past thirty to forty years, the Sahel--a loosely

defined band across Africa, just south of the Sahara and including

parts of Ethiopia

in the east and Guinea in the west--has suffered the most

sustained drought seen in any part of the world since records began,

with precipitation falling by between 20 and 50 per cent.

 

Although the droughts have had climate experts scratching

their heads, the impacts have been obvious. During the worst years,

between 1972 and 1975, and 1984 and 1985, up to a million people

starved to death.

 

Now Leon Rotstayn of the CSIRO, Australia's national

research agency, thinks he knows what caused them. Rotstayn and his

colleague Ulrike Lohmann of Dalhousie University in Halifax, Nova

Scotia, ran a simulation of global climate that included interactions

 

between sulphur dioxide emissions and cloud formation. Sulphur

dioxide creates sulphate aerosols that provide condensation nuclei

for clouds. With more nuclei, clouds  form from

smaller droplets than usual, and are more efficient at

reflecting solar radiation, cooling the Earth below.

 

Acid rain

 

When the researchers included the huge sulphur emissions

from the northern hemisphere during the 1980s in their model, the

Earth's surface

in the north cooled relative to the south, driving the

tropical rain belt south and causing droughts in the Sahel. Their

results will be reported soon in the Journal of Climate.

 

" It's still speculative, and the model isn't very refined,

but it's very

interesting. It's the first time we've seen a connection

between

pollution in the mid-latitudes and climate in the tropics, "

says Johann

Feichter of the Max Planck Institute for Meteorology in

Hamburg.

Feichter, who has run similar simulations but cannot talk

about the results because the research

is being peer-reviewed for a major journal, says the

sulphur emissions probably worsen the natural cycle of droughts that

would have happened anyway.

 

During the past few years, the droughts have become less

severe, a change that Rotstayn puts down to the " clean air " laws in

North America and Europe that reduced sulphur dioxide emissions in

response to another environmental crisis, acid rain.

But the problems in Asia may be just beginning. Climate

researchers

around the world are beginning to study other types of

aerosols, such as

the clouds of black soot and sulphate being churned out by

rapidly

industrialising India and China, in the hope that they may

shed light on

other regional weather anomalies. For instance, northern

China has had unusually dry summers in the past few years, while it

has been particularly wet in the south.

 

Rachel Nowak, Melbourne

http://www.newscientist.com/news/print.jsp?id=ns99992393

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david camilleri

ghawdex40

http://www.MaltaTouristAction.org

 

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