According to an article published last week in The Guardian (based on a report by Bloomberg New Energy Finance for the Business Council for Sustainable Energy), U.S. carbon dioxide emissions are at their lowest level since 1994.
(A separate report from Resources for the Future reached similar conclusions, The Guardian says.)
Moreover, U.S. carbon dioxide emissions are down 10.7 percent from 2005 levels, which puts the U.S. most of the way toward President Obama's goal of cutting emissions to 17 percent below 2005 levels.
The reduction is due largely to increased use of natural gas rather than coal in electricity generation. Burning natural gas produces more usable energy relative to the CO2 produced. Unfortunately, natural gas extraction appears to release more methane into the air, which is itself a greenhouse gas, and that likely offsets at least some of the advantage of reducing CO2 output.
Part of the reduction also stems from the growing use of wind, solar, and other non-fossil-fuel energy sources, which present many fewer offsetting problems, and part comes from reduced energy consumption from such things as incremental improvements in average gas mileage, better building insulation, etc.