Every month of 2012, from January to October, saw monthly energy related carbon emissions lower than in the corresponding month in 2011. That trend to lower emissions reversed in November 2012.
For the first time in a year, US monthly carbon emissions rose in November 2012 when compared to November 2011. http://www.eia.gov/totalenergy/data/monthly/pdf/mer.pdf. See table at Chapter 12.1 of the link that shows November 2012 carbon emissions were 7 million tons higher than a year before.
Total carbon emissions in 2012 will be considerably lower than in 2011, but November, 2012 may well mark the beginning of a trend toward higher emissions in 2013 than in 2012.
The rise in energy related carbon emissions in November 2012 was substantially the result of a 12% drop in monthly nuclear generation or 8 billion kilowatt-hours less nuclear power and 7 billion kilowatt-hours more of coal generation. See Chapter 7 of the above link.
Indeed, monthly coal generation increased during November 2012, when compared to November 2011, also for the first time in a year.
Coal, nuclear power, and gas remain the big 3 power generation sources, providing about 87% of all electricity in the USA. The market share of each drives heavily total US carbon emissions. That's a fact, whether recognized or not.