The National Oceanic and Atmospheric Administration officially designated 2012 as the warmest year on record for the contiguous United States. This isn't too surprising for a year that already had the warmest spring, the second warmest summer and fourth warmest winter. The average temperature for 2012 was 55.3°F, 3.2°F above the 20th century average, and a full 1.0°F above 1998, the previous record holder.
Climate expert Anthony Barnston, who is the chief forecaster at Columbia's International Research Institute for Climate and Society, explains some of the climate factors behind this record-breaking year in a video interview.