Though global carbon-dioxide emissions increased 3.2 percent last year, U.S. emissions declined by 1.7%. Part of this can be attributed to a mild winter. But as the International Energy Agency notes, the decline since 2006 has been notably sharp:
CO2 emissions in the United States in 2011 fell by 92 Mt, or 1.7%, primarily due to ongoing switching from coal to natural gas in power generation and an exceptionally mild winter, which reduced the demand for space heating. US emissions have now fallen by 430 Mt (7.7%) since 2006, the largest reduction of all countries or regions. This development has arisen from lower oil use in the transport sector (linked to efficiency improvements, higher oil prices and the economic downturn which has cut vehicle miles travelled) and a substantial shift from coal to gas in the power sector.
One assumes that a robust recovery will erase at least some of these gains, but an interesting finding all the same.