FILE- This Wednesday, Feb. 29, 2012, file photo, shows Midwest Generation’s Crawford Generating Station, a coal-fired power plant, in Chicago. The share of U.S. electricity that comes from coal has fallen to its lowest level since World War II. Utilities are aggressively ditching coal in favor of natural gas, which has become cheaper and produces far fewer emissions of toxic chemicals and gases that contribute to climate change. (AP Photo/M. Spencer Green, File)