for National Geographic News
Planting trees might not be such a good idea in the fight against global warming—at least not in high latitudes.
That's the implication of new research that finds that forests in parts of Canada, Siberia, and Scandinavia could absorb enough sunlight to warm those areas some 10 degrees Fahrenheit (5.5 degrees Celsius) over the next century compared to if those forests didn't exist.
The results appear this week in the online edition of the Proceedings of the National Academy of Sciences.
They run counter to long-standing arguments that planting trees anywhere in the world is an effective way to combat global warming (get global warming fast facts).
The new study supports the practice in rain forest zones, where more trees absorb more carbon dioxide from the atmosphere.
Tropical plants also produce more water vapor, adding to the thick cloud cover that reflects sunlight back into space.
But the dark canopies of northern forests absorb the sun's rays and cover the snow that would reflect light, creating a regional warming effect.
(Related news: "Forests Have Replaced Tundra Due to Warming, Study Finds" [March 9, 2007].)
"If you look down from an airplane, where you have seasonal snow cover and you don't have a forest, it's all white, and that snow is highly reflective," said study co-author Govindasamy Bala, an atmospheric scientist at Lawrence Livermore National Laboratory.
"If you plant new trees, the canopy covers that snow and very little sunlight is reflected. That's why when you plant trees there is a potential for locally warming a place."
William Laurance, an ecologist at the Smithsonian Tropical Research Institute in Panama, said that the new study will produce strong reactions among environmentalists.
SOURCES AND RELATED WEB SITES