The average annual temperature for the continental United States (excepting Alaska) was the warmest on record, according to the National Climate Data Center (NCDC), a division of the U.S. Department of Commerce National Oceanic & Atmospheric Administration (NOAA).
The 2006 average annual temperature in the “lower 48” states was 55° F, which is 1.2° F above the average for the 20th Century and just 0.07° F above the previous record, set in 1998.
Through November, 2006 was on track to be the third warmest year on record, but mild December temperatures through the eastern two-thirds of the continental U.S. pushed the year to record-breaking warmth.
Unusually warm temperatures during much of the first half of the cold season (October – December) helped reduce overall residential energy needs in the U.S., the NCDC scientists added. Using an index developed at NOAA to relate energy usage to climate, scientists determined that the nation's residential energy demand was some 13.5% lower than what it would have been under average climate conditions for the season.
Five states had their warmest December on record—Connecticut, Minnesota, New Hampshire, New York and Vermont. No state was colder than average in December.
Scientists said that an "El Nino episode" in the equatorial Pacific and a long-term warming trend, "linked to increases in greenhouse gases," were the primary causes for the unusually warm start to the 2006-2007 winter.
U.S. and global annual temperatures are now approximately 1° F warmer than at the start of the 20th Century, NOAA scientists say. The rate of warming has accelerated over the past 30 years and the past nine years have all been among the 25 warmest years on record for the contiguous U.S., a streak that is unprecedented in the historical record, they added.