Global warming's latest villain: soot

Move over greenhouse gases. A new villain is muscling onto the global warming scene. It's called soot. Research published today shows it probably is second only to carbon dioxide as a pollutant with heat-trapping power.

Climatologists have become increasingly suspicious of black carbon particles in recent years. However, their abundance and distribution in the atmosphere are hard to determine. Their sources are poorly known. Their heat-trapping ability depends on how they clump together and join with other substances to make larger particles. Now Mark Jacobson at Stanford University has integrated what is known into a computer climate simulation.

With this, he has explored the probable climatic influence of a variety of particle compositions and their global distribution. He explains in the journal Nature why he thinks this study suggests that controlling black-particle pollution "may be as - or more - beneficial" than controlling the potent greenhouse gas methane.

This adds a new dimension to the global warming discussion. The Kyoto Protocol of December 1997 that proposed controversial curbs on greenhouse gases ignored black-carbon particles. Scientists didn't know enough about them. They did know that methane from agriculture and animal husbandry is next in line after carbon dioxide as a gaseous pollutant driving global warming. It's on the Kyoto hit list. Now Dr. Jacobson's simulations show that the atmosphere's average load of sooty particles have more warming power than the air's methane.

However, as Meinrat Andreae with the Max Planck Institute for Chemistry in Mainz, Germany, points out in a commentary accompanying Jacobson's paper, particles are not gases. Carbon dioxide and methane linger in the atmosphere for decades. Particles wash out in a week. Curbing short-lived soot would bring an instant climate benefit. Moreover, pollution-control authorities are increasingly concerned about soot as a health hazard. It should be easier politically to justify the cost of curbing soot emissions from diesel engines and dirty smoke stacks than to persuade reluctant governments to cut back on carbon dioxide.

But, as both Jacobson and Dr. Andreae noted, scientists first have to identify where the soot is coming from. Some comes from diesel engines. Some from biomass burning - especially in Africa, parts of Asia, and South America. Sources of much of it - especially from dirty factories and power plants - are not well known. Meteorologists were surprised in 1999 when measurements over the Indian Ocean found that a plume coming from Southern Asia boosted their estimate of global sooty pollution by as much as 25 percent.

Natural fires in high-latitude Northern Hemisphere forests are a wild card in such estimates. Fire severity has increased significantly in these forests over the past 20 years as the planet has warmed, according to reports given at a meeting of the American Geophysical Union in San Francisco last December.

The bottom line, according to Andreae and Jacobson, is there now is a strong reason to devote substantial resources to researching the role of black-carbon particles in global warming.

(c) Copyright 2001. The Christian Science Publishing Society

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