The United States-China agreement on climate change is a huge political triumph, possibly "historic," as its supporters say. Whether it much alters the world's climate is a more open question.
Recall the agreement's outlines. By 2030, China pledges to reach peak emissions of global greenhouse gases and also to increase its reliance on non-fossil fuels to 20 percent of its total energy. For its part, the U.S. committed to reducing its greenhouse gas emissions in 2025 by 26 percent to 28 percent from 2005 levels.
Environmentalists correctly see three big gains.