Smoke Signals

Why are the world's forests burning? Why did uncontrollable fires cut a 7,700-sq.-mi. swath of devastation across Indonesia? Why have the blazes of Mexico sent plumes of smoke across Texas and Louisiana?

Here's the simple answer: El Nino. While that notorious weather system flooded some regions, it produced horrendous droughts in other areas, making half the world a tinderbox.

But that's too easy an explanation. Scientists suspect that something more fundamental--and frightening--is happening. In one country after another, flames are going where they've never gone before. "These fires are burning into virgin, humid forests that have evolved without fire," says Nels Johnson of Washington's World Resources Institute. "There is no historical precedent for the fires in the cloud forests of the Lacondon region of Mexico." Fire storms in the rain forests--the very idea defies common sense--have become an unmistakable distress signal from the developing world.

Even without the effects of El Nino, forests are increasingly vulnerable, and the blame lies with human activity. People are literally paving the way for fire's intrusion. Roads penetrating tropical forests provide access to loggers, peasant farmers, ranchers and plantation owners, all of whom use fire to clear land. Logging in particular creates incendiary conditions by leaving combustible litter on the forest floor and allowing sunlight to penetrate the forest canopy and dry out the vegetation.

A rain forest is a self-perpetuating system in that water vapor from trees energizes rainstorms. Cut the trees and rainfall decreases, further drying a system that is not adapted to recovering from fire. Experts wonder if this is why denuded southern China has seen a decline in rainfall this century, and why West Africa has lost one of two rainy seasons. Looming over all rain forests is the threat of global warming caused by human emissions of greenhouse gases. Computer simulations suggest that the greenhouse effect will increase the frequency of drought in tropical areas.

Belatedly, rains have come to Southeast Asia in recent weeks, and they are still expected in Mexico, but any relief is likely to be temporary, and dryer conditions will return later in the year. Experts are particularly worried about Brazil, where a new dry season is just starting. Daniel Nepstad, a tropical-forest ecologist at the Woods Hole Research Center in Massachusetts, notes that "the eastern Amazon is teetering on the edge." The region has received one-fifth of its normal rainfall in the past year, and Nepstad says an area 20 times the size of Massachusetts is at risk.

The tragedy goes far beyond the countries that are burning. Besides worrying about the loss of tropical forests, with their unmatched natural resources, policymakers have to be concerned about the clouds of smoke that have endangered public health from Singapore to Houston. But so far it's been easier to announce programs to combat the fires than to get at the causes. In April the United Nations Environment Program called for a $10 million fund to help Southeast Asia contain its fires. Washington has contributed $7.5 million to Mexico's firefighting efforts.