"While coal is one of the most widely used fossil fuels, unfortunately, it's also one of the dirtiest. Burning coal causes smog and acid rain, and in an average year, a coal plant may generate 3.7 million tons of carbon dioxide, which is one of the leading causes of global warming. In the United States, coal provides about 50 percent of all electricity, and the U.S. Department of Energy predicts that more than 150 new coal-fired power plants might be constructed by the year 2025." (Quoted from article)