Developments to Watch
FEWER TREES MEAN GLOBAL WARMING--BUT SO DO MORE TREES
Scientists know that rain forests play a role in setting the earth's temperature. Cutting them down can cause global warming. But jungles aren't the only forests that affect climate. In a study in the Oct. 22 issue of Nature, climatologist Gordon B. Bonan and colleagues at the National Center for Atmospheric Research report that the vast boreal forests stretching around the northern part of the world can boost--you heard it right--global warming.
The boreal evergreen blanket absorbs up to three times as much solar radiation as snow-covered tundra, Bonan found. As a result, his computer model shows that winter temperatures are 21F higher in the Arctic--and 3F higher at the equator--than they would be without the trees.
This phenomenon helped the earth warm up from the last ice age. But if the globe gets warmer because of rising levels of CO2 and other greenhouse gases, as many scientists expect, the boreal forests will respond by expanding north. "That geographic change in tree line could cause an additional climate warming," says Bonan. The results also mean that cutting down the boreal forests would be a sure, if ecologically disastrous, way to help cool off the earth.EDITED BY WILLIAM D. MARBACH