It seems likely due to a recent, steady rise in natural gas prices:
and fracking looks unlikely to lead to much more reduction in CO2 emissions;
Note the small "X" in the chart, indicating the 17% emissions cut by 2020 (below 2005 levels) that President Obama pledged at Copenhagen. Doesn't look like we're going to be hitting that....
Right now US emissions for the past 12 months are at 5.304 Mt CO2/yr, down 732 Mt CO2/yr (12.1%) from their peak. Per capita emissions are at 16.9 t CO2/yr, down a whopping 25% from their December 1973 level of 22.3 t CO2/yr. (That's as far back as the EIA monthly data goes, though I'm sure there is annual data somewhere.)