A coal scraper machine works on a pile of coal at American Electric Power's Mountaineer coal power plant in 2009 in New Haven, W.Va. The state, in which coal mining is a major industry, is one party planning to sue the Environmental Protection Agency regarding new power plant regulations announced Monday. Saul Loeb/AFP/Getty Images hide caption

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A plume of steam billows from the coal-fired Merrimack Station in Bow, N.H. in January 2015. Jim Cole/AP hide caption

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Stanford University's trustees says the school will rid itself of any investments it has made in coal-producing companies. A 2013 file photo shows coal being loaded onto a truck at a mine near Decker, Montana. Matthew Brown/AP hide caption

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Several tons of anthracite coal fill a basement space in Pottsville, Pa. Bradley C. Bower/AP hide caption

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A memorial at the entrance to Massey Energy's Upper Big Branch coal mine represents the 29 coal miners who were killed in an explosion in 2010. Jeff Gentner/AP hide caption

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The city of Gladstone near the Great Barrier Reef is the world's fourth largest coal-export hub. Dredges, like one seen here, have turned the harbor brown as they work to expand the coal port. Richard Harris/NPR hide caption

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China and India are projected to propel coal's challenge of oil as the world's top energy source within the next five years, according to a new study. Here, a man rides a bicycle toward a coal-fired power station in China's Guangdong province last year. Mark Ralston/AFP/Getty Images hide caption

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Wreaths and flowers commemorating those killed in the Crandall Canyon Mine collapse are posted at the mine entrance on Dec. 10, 2007, outside Huntington, Utah. A settlement Thursday includes mine owner Murray Energy's acceptance of four violations considered "contributory" to two fatal August 2007 mine collapses at Crandall Canyon. Douglas C. Pizac/AP hide caption

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