Washington, D.C. ? Climatologists have worried for years that forest fires would worsen global warming by adding carbon dioxide to the atmosphere. Now, there is an indication that the fires could have a regional cooling effect.

Fires in northern forests do release greenhouse gases that contribute to climate warming. But they also cause changes in the forest canopy that result in more sunlight reflected back into space during spring and summer for many decades after the fire, said James T. Randerson, associate professor of earth system science at the University of California, Irvine.

“This cooling effect cancels the impact of the greenhouse gases,” he said. “The net effect of fire is close to neutral when averaged globally, and in northern regions may lead to slightly colder temperatures,” said Randerson, lead author of a study appearing in today’s issue of the journal Science.

The study looked at the Donnelly Flats fire in central Alaska, which burned 16,549 acres in 1999.