International wrangling over ways to control the greenhouse gases that drive global warming is the prelude to a larger debate. Scientists now find that the dust, soot, and other microscopic particles we kick into the atmosphere are also potent climate changers. Nations will have to find ways to reduce this dirty, airborne - or aerosol - pollution, as well as curb carbon dioxide emissions, to avoid possibly unpleasant environmental changes.
It won't be easy. Cleaner, more efficient energy use and production can cut back both carbon dioxide emissions, the chief man-made greenhouse gas, and some aerosol pollution. But that would only begin to solve the aerosol problem. A recent expedition studying the man-made haze over the Indian Ocean found this problem to be far larger and more complex than scientists have realized.
Scientists had thought the main climate effect of aerosols would be regional cooling as the particles scattered sunlight back into space. Instead, the Indian Ocean researchers found a thick pall over an area as large as the continental United States. It absorbed sunlight and warmed up. Black soot and other heat-absorbing particles offset the cooling effect. Moreover, they reduced the sunshine reaching the surface enough to cut back growth of the microscopic algae that underlie marine food chains.
The researchers concluded that aerosol palls can effect climate in ways they don't fully understand. Aerosols may offset or enhance global warming. They may affect cloud cover and reduce precipitation significantly. They can affect marine food chains.
What happened over the Indian Ocean raises a global concern. Pollution from China, India, and other parts of southeast Asia had spread over a vast area. Research elsewhere has traced Asian particle plumes across the pacific. North American plumes reach far over the Atlantic. Some of these plumes contain more soot and other dark matter than others. But all are becoming extensive enough to have far-reaching environmental effects.
These aerosol palls arise from a variety of sources which, in the aggregate, will be hard to control. In southeast Asia, coal-burning industry and millions of wood-burning and dung-burning homes contribute dirty particles. Elsewhere, slash-and-burn farming on a massive scale is at fault. In regions like North America, aerosols come from trucks, leaf blowers, and other such dispersed sources, as well as from industry.
Controlling this kind of pollution would mean fundamental changes in long-established lifestyles in many parts of the world. Curbing carbon dioxide emissions seems simple by comparison. As population grows, aerosol pollution will worsen. Nations cannot continue to ignore it. Building global consensus to deal with greenhouse gases is a tough diplomatic exercise. It's only a warm-up for the coming aerosol challenge.
(c) Copyright 1999. The Christian Science Publishing Society