The project wasn't started as a global warming fix. As the article notes, it was about preventing desertification:

> Over the last three and a half decades China has planted roughly 120 million acres of forest, according to U.N. figures, much of it added to contain the spread of deserts. Last year China completed a project, begun in 1978, to plant a 2,000-mile-long belt of trees around the Taklamakan Desert in the west. Work continues on a belt of trees around the massive Gobi Desert in the north.