The Environmental Protection Agency has proposed tighter limits on mercury, sulfur dioxide and other pollutants that would make it more expensive for utilities to burn coal, a major source of those emissions. The EPA has also proposed limiting the amount of carbon dioxide that new power plants can emit.Neither would specifically bar coal-fired power plants, but experts say it would be nearly impossible to build an affordable new coal plant that could meet the limits. The proposals, some which had begun under George W. Bush's administration, wouldn't affect coal plants now in use or being built. Obama, who during his 2008 campaign said builders of new coal-powered plants will go bankrupt from emissions standards he would enact, now espouses an "all of the above" energy strategy that includes coal. "The president has made clear that coal has an important role to play in our energy economy today and it will in the future, which is why this administration has worked to make sure that moving forward we can continue to rely on a broad range of domestic energy sources from oil and gas, to wind and solar, to nuclear, as well as clean coal," Clark Stevens, a White House spokesman, said recently. What's happening in the coal industry is more than a seasonal slump or a response to new regulations; even coal executives admit it's a fundamental shift. Many utilities have switched from coal to cheaper natural gas for electricity generation, pushing up coal stockpiles at power plants and forcing mining companies to sharply cut production. When St. Louis-based Patriot Coal filed for bankruptcy in July, it didn't mention a war on coal but cited "a major correction" in the industry and "new realities in the market," including fierce, sustainable competition of natural gas. But St. Louis-based Arch Coal Inc. blamed market pressures and a challenging regulatory backdrop in its June announcement it would lay off about 750 Appalachian coal workers.