Trees May Be Bad for You.

In the effort to slow earth's rising temperatures, even a well-intentioned proposal could backfire, scientists said Wednesday.

One suggestion has been to grow more trees, which absorb carbon dioxide, the gas blamed for trapping heat. More trees mean more carbon dioxide removed from the air.

New computer simulations, however, indicate that establishing new forests across North America could provide a cooling effect for a few decades to a century, but that after that, they would lead to more warming.

"There's really no simple answer," said Ken Caldeira, a scientist at the Carnegie Institution Department of Global Ecology in Stanford, Calif., who presented the research at a meeting of the American Geophysical Union here. "At least in this calculation, there is predicted to be a net warming effect."