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U.S. pollution behind African drought

By Gary Wilson

The African drought from 1970 to 1985 killed 1.2 million people in one of the most devastating famines ever known. A new study by scientists from Australia and Canada has concluded that the cause was sulfur dioxide spewed out by factories and power plants in the United States, Canada and Western Europe.

The pollution of North America and Europe disrupted weather patterns, dramatically changing the temperature of the Earth's surface. This led to a reduction in rainfall by as much as 50 percent in the Sahel region of Africa that stretches from Senegal to Ethiopia.

Tiny airborne particles called sulfate aerosols, which are found only in the highly industrialized countries, boost the number of small droplets in clouds; researchers have found that this extends the lifetime of clouds. Some suspect that the particles also make clouds reflect more sunlight, cooling Earth's surface below, reducing evaporation, and ultimately decreasing rainfall.

"Global climate change is not solely being caused by rising levels of greenhouse gases. Atmospheric pollution is also having an effect," says Leon Rotstayn, the Australian scientist who headed the study.

According to Rotstayn, the sulfate aerosol pollution concentrations are far greater in the Northern Hemisphere, cooling the atmosphere there more than in the Southern Hemisphere. It is this imbalance that affects the tropical rain belt. As a result, the tropical rain belt, which migrates northwards and southwards with the seasonal movement of the sun, is weakened in the Northern Hemisphere and does not move as far north.

The New Scientist magazine quotes another scientific researcher, David Roberts:

"It's an effect of the thermal balance between the two hemispheres. There has to be a rough balance between the north and south hemispheres--you can't have spare energy in one place or the other. If the Earth was completely symmetrical, then the point of thermal equilibrium, where the total energy on either side of a line was equal, would be the Equator. But because the Northern Hemisphere isn't the same as the south [because of the vast energy reservoir of the Pacific, which retains energy more efficiently than land] we find that the Northern Hemisphere is warmer than the South."

However, the cooling of the Northern Hemisphere by aerosol pollution pushes the point of thermal equilibrium south--and with it go the rain clouds that had covered the Sahel. It may also explain the flooding rains that are now sweeping southern Africa.

One change that the researchers cite in the study occurred in the 1980s. At that time, improvements in anti-pollution laws meant that sulfur emissions dropped because they were blamed for acid rain. Following that change, the droughts in Africa became less severe.

With the new understanding of the connection between sulfate aerosol pollution and rainfall, the position taken by Washington administrations from George W. Bush to Bill Clinton can no longer be sustained. Washington had claimed that nothing needed to be done about global warming because the aerosol pollution cools the Earth. Now it has been shown that this kind of cooling contributes to changing weather patterns in ways that are disastrous for millions of people, just as are the rising sea levels caused by global warming.

Reprinted from the Aug. 29, 2002, issue of Workers World newspaper
This article is copyrighted under a Creative Commons License.
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