Coal pollution mitigation emissions of sulfur dioxide or oxides of nitrogen associated with the utilization of coal in the generation of electricity." Before being adopted in this fashion, historically "clean coal" was used to refer to clean-burning coal with low levels of impurities, though this term faded after rates of domestic coal usage dropped. The term appeared in a speech to mine workers in 1918, in context indicating coal that was "free of dirt and impurities." In the early 20th century, prior to World War II, clean coal (also called "smokeless coal") generally referred to anthracite and high-grade bituminous coal, used for cooking
Coal mining year. The United States was ranked as the second highest coal producing country in the world in 2010, and possesses the largest coal reserves in the world. In 2008 then-President George W. Bush stated that coal was the most reliable source of electricity. However, in 2011 President Barack Obama said that the US should rely more on "clean" sources of energy that emit lower or no carbon dioxide pollution. For a time, while domestic coal consumption for electric power was being displaced by natural gas, exports were increasing. US net coal exports increased ninefold from 2006 to 2012, peaked at