http://www.nytimes.com/2013/01/09/science/earth/2012-was-hottest-year-ever-in-us.html?hp&_r=0

How hot was it? The temperature differences between years are
usually measured in fractions of a degree, but last year’s 55.3 degree average
demolished the previous record, set in 1998, by a full degree Fahrenheit.

If that does not sound sufficiently impressive, consider that 34,008 daily high
records were set at weather stations across the country, compared with only
6,664 record lows, according to a count maintained by the Weather Channel
meteorologist Guy Walton, using federal temperature records.

That ratio, which was roughly in balance as recently as the 1970s, has been out
of whack for decades as the country has warmed, but never by as much as it was
last year.