The nation’s biggest business lobby says President Barack Obama ’s plan to tackle climate change could cost the U.S. economy $50 billion a year. Supporters predict it will create jobs and lower power bills. The U.S. Chamber of Commerce and Natural Resources Defense Council are both releasing economic impact studies this week, signaling that the political battle over the president’s plan will be fought over dollars and cents. For Obama, the risk is the plan gets labeled a job-killer just as campaigns heat up for an election that could determine control of the U.S. Senate . In an analysis set for release today — days before the Environmental Protection Agency unveils a proposal to cut carbon dioxide emissions from power plants — the Chamber says that an ambitious pollution-control effort could force more than a third of the coal-fired power capacity to close by 2030, resulting in economic losses […]