Between 2007 and 2011, carbon emissions from coal use in the United States dropped 10 percent. During the same period, emissions from oil use dropped 11 percent. In contrast, carbon emissions from natural gas use increased by 6 percent. The net effect of these trends was that U.S. carbon emissions dropped 7 percent in four years. And this is only the beginning.
– Lester Brown, “U.S. Carbon Emissions Down 7 Percent in Four Years: Even Bigger Drops Coming,” Earth Policy Institute, 2 November 2011