Bailey Coal Mine in Wind Ridge Pa. serves up 45,000 tons of coal per day

Coal produces nearly half the electricity in the U.S., but the mercury, sulfur dioxide and carbon dioxide it emits also make it one of the most controversial energy sources. New EPA regulations and a national Sierra Club campaign have added to rising anti-coal sentiment. For many environmental activists, coal represents an old, dirty source of power, but for coal-mining communities around the country, the story is different. Video by Kimberly Paynter.