- The Washington Times - Monday, September 16, 2002

An Australian scientist says that air pollution from far-off cities may be playing a role in the Sahel drought in northern Africa by preventing the northward movement of the tropical rain belt.
The Sahel is an area that extends across Africa on the southern edge of the Sahara desert. Every year the desert moves scores of miles southward because of desertification and erosion, while the Sahel shrinks at an alarming rate.
"The Sahelian drought may be due to a combination of natural variability and atmospheric aerosol. Cleaner air in the future will mean greater rainfall in this region," Leon Rotstayn, an Australian government researcher, said in a recent report.
Aerosols are created by both natural and human sources, such as the burning of fossil fuels and biomass. In an aerosol, tiny particles act as small nuclei on which cloud droplets can form. In high concentrations, these will result in brighter clouds, causing more solar energy to be reflected back into space and lowering temperatures in polluted areas or altering global rainfall patterns.
"Global climate change is not solely being caused by rising levels of greenhouse gases. Atmospheric pollution is also having an effect," Mr. Rotstayn said. Many scientists believe that greenhouse gases, such as carbon dioxide, are responsible for the warming of Earth's atmosphere.
But Mr. Rotstayn says he has new evidence that aerosols from power-generation and industry in the north could be far more significant in disrupting the regional climate in poor nations in tropical Africa.
"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 midlatitudes and climate in the tropics," said Johann Feitchter of the Max Planck Institute for Meteorology in Hamburg, Germany.
On a positive note, Mr. Rotstayn said that a reduction in the severity of the Sahel drought in the 1990s could be linked to emission controls in Europe and North America that lowered levels of atmospheric pollutants.
But Patrick J. Michael, a senior fellow at the Cato Institute who specializes in environmental studies, said he is skeptical of the Australian's research.
The Sahel region clearly was overgrazed in the past, which resulted in raised surface temperatures and put large quantities of dust in the air, Mr. Michael said in an interview.
"The effect on regional climate from desertification and overgrazing is much larger than the effect on regional climate from sulfate aerosol," he said.
Scientists generally are reluctant to apply existing models of global climate change to regions because the results are considered unreliable, he said.
U.N. Secretary-General Kofi Annan recently highlighted the dangers of desertification to northern Africa. He said that in the next 20 years, about 60 million people are expected to leave the Sahel if desertification is not stopped.
"Every year, an estimated $42 billion in income and [about 15 million acres] of productive land are being lost because of desertification, land degradation and declining agricultural productivity, and 135 million people who depend primarily on land for their livelihood are at risk of being displaced," Mr. Annan said in a message to mark World Day to Combat Decertification and Drought.
"We need to reverse the decline in agricultural productivity, especially in Africa, so that food production keeps pace with the number of mouths to feed," he said.
"The fight against desertification is fundamentally a fight against poverty," said Hama Arba Diallo, executive secretary at the U.N. Convention to Combat Decertification and Drought.
"We need to find ways to halt land degradation and to manage land more responsibility" Mr. Annan said.

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