It is far from clear that the United States government will actually plant any trees, or that a trillion trees would do much in the near term to stop the worst effects of planetary warming.
Tom Crowther, an environmental scientist and an author of the study that sparked the movement, cautioned that the full benefits would not be seen for about 100 years, when most of the new trees would reach full maturity. During that time, he said, the world needs to drive down fossil fuel emissions.
“If tree planting is just used as an excuse to avoid cutting greenhouse gas emissions or to further limit environmental protection, then it could be a real disaster,” said Dr. Crowther, who studies ecosystem ecology at ETH Zurich.