Coal, the fire stone, filler of Christmas stockings, enabler of industrialization, may be reaching its peak. "The peak of global coal production... is imminent," wrote two engineering professors, in the journal Energy in 2010.
Like other peak assessments, coal projections vary with researchers' assumptions and estimates. The Energy Watch Group, based in Germany, has suggested that U.S. coal production peaked in 2002 and that world reserves could climb until 2025. The U.S. Energy Information Agency sees global coal output rising at 1.1 percent a year at least until 2035.
Coal has always been dirty. Airborne soot convinced Londoners in the 1700s to start using all-black umbrellas to hide the grime, a tradition that's carried on even after the air has cleared significantly. Today, the grime from coal is molecular, as power plants release carbon dioxide emissions that contribute to global warming.
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