Washington Post: IT’S NOT Plan A, B or even C, but if Congress continues to do nothing on climate change, environmentalists can at least take heart that some states are planning to cut greenhouse emissions on their own. As usual on such issues, California leads the way, with a robust greenhouse gas law mandating a reduction in the state’s emissions to 1990 levels by 2020, which its state legislature approved in 2006. But even that could be undone on Tuesday, when voters consider Proposition 23, an oil-company-backed…