Data released today by the National Climatic Data Center indicate 2012 will be the warmest year ever recorded in the United States. Record-keeping began in 1895.
From the center's November 2012 climate report:
It appears virtually certain that 2012 will surpass the current record (1998, 54.3°F) as the warmest year for the nation. December 2012 temperatures would need to be more than 1.0°F colder than the coldest December (1983) for 2012 to not break the record.
The December 2011-November 2012 period was the warmest such 12-month period on record for the contiguous U.S., with an average temperature of 55.2°F, 3.2°F above average. This 12-month temperature average was the sixth warmest of any 12-month period on record for the contiguous United States. The eight warmest 12-month periods have all ended during 2012.
And now this cool graphic from the report: