"Thanks to the recession, improved efficiency measures and the shale-gas boom, the nation's carbon-dioxide emissions from energy fell 12 percent between 2005 and 2012," observes Brad Plumer. "But the party's now officially ending, at least for those worried about global warming. In an early estimate, the U.S. Energy Information Administration says that U.S. carbon-dioxide emissions from energy sources increased 2 percent in 2013."
The shift from coal to gas-powered generators by electric utilities was a major cause of the prior decline. But with natural gas prices on the rise, coal use has increased as have carbon emissions.