Arch Coal Inc (NYSE:ACI) has said that it’s currently impossible for coal plants to run with the near-zero carbon emissions that would be required under a new proposal from the Obama Administration, AP News reports. Carbon emission standards Obama’s proposal, which is similar to one announced last year, limits carbon emissions from new plants and sets limits on total national emissions. Existing plants won’t be affected in the short-term, but they will eventually have to reduce emissions, and new coal-powered plants are effectively banned under the proposal. Moving the U.S. away from coal, which currently supplies 40 percent of the nation’s…