Northern smoke 'to blame for Africa's drought'

Posted: 14 June 2002

New research indicates that pollution from factories and power stations, especially in North America and Europe, has exacerbated drought in countries south of the Sahara.

Researchers have little doubt that the two are connected and also that the effect of the drought will last long after any clean-up.

There are also warnings that growing industrialisation in India and China is likely to create the same problems on the Indian subcontinent - with potentially disastrous effects for millions more people.

According to a report in New Scientist magazine (13 June 2002), climate modelling studies by scientists in Australia and Canada point a finger at the clouds of sulphur poured out by vehicles and power stations when they burn fossil fuels for pushing the Saharan rain-belt south.

The scientists, Leon Rotstayn of CSIRO, the national research agency in Australia, and Ulrike Lohmann, of Dalhousie University, in Halifax, Nova Scotia, created a computer model that simulated the interactions between sulphur dioxide emissions from power plants and other sources.

These emissions create huge volumes of "aerosols" - tiny particles about one micrometre across that can remain floating in the atmosphere for days. They are very efficient at scattering light and forming clouds, which reflect sunlight; both effects tend to cool the atmosphere and the Earth below.

The vast amount of aerosols produced especially in the 1980s lingered over the northern hemisphere and tended to cool it down, say the researchers. But it is the final step - to the shifting fortunes of the rain clouds that should linger over the Sahel - which is the subtle one.

It seems that this aerosol-driven cooling of the Northern hemisphere pushes that point of thermal equilibrium south - and with it go the rainclouds that people depend on for their crops in the Sahel.

The historical evidence tends to back up the findings.

Dr David Roberts, head of the aerosol modelling group at the Meterological Office's Hadley Centre for Climate Prediction and Research, says he is "cautious" about taking the interpretation of the link between aerosols in the northern hemisphere and the weather in the Sahel as gospel. However, he says that if it is correct, then there are other areas around the globe that could be threatened by a new wave of fossil-fuel burning.

"The emissions from China and India are rising," he said yesterday. "And that could affect, for example, the monsoon season in India, which would have an important regional impact. If it weakens the monsoon, then that would be a concern. The subcontinent is very dependent on it; it would be of serious concern to them if that moved. But the aerosols would alter the balance between north and south in the same way."

What is unclear is how the world would cope with change like that. In the Sahel, drought is becoming ingrained: without water, vegetation dies, and the the dry land and the dust thrown up from it into the atmosphere both reflect heat, keeping the thermal equilibrium point in its southerly place. And when it does rain, the lack of plant life means that water just runs away.

"It's a vicious cycle, a land degradation issue," Habiba Gitay, an ecologist who worked on the Intergovernmental Panel on Climate Change told New Scientist. And the blame for starting the cycle turning appears to lie with the developed world. The problem, though, is that nobody knows quite how to stop it and bring back the rain to the places that need it.

This is an shortened version of a report from The Independent (UK), 13 June 2002.