The Wall Street Journal claimed that, "U.S. carbon-dioxide emissions have fallen dramatically in recent years, in large part because the country is making more electricity with natural gas instead of coal."
According to CO2 Scorecard, a policy initiative for tracking progress towards climate friendly economic growth, they contributed the causes of decline to the economy-wide energy efficiency and conservation measures in the
transportation, residential and commercial sectors, and the mild winter in
the first quarter of 2012. The contribution of natural gas in
the electric power sector was limited to around 26% of the total energy
related CO2 reduction in 2012.
I guess it is important to know where emission reduction comes from to better tackle the global climate change. When you can't generate enough then you should reduce and use efficiently. Energy-efficiency definitely plays an important role on today economy and environment.
For more detail of the report please visit Demand Reduction Slashes US CO2 Emissions in 2012