The average annual temperature for the contiguous U.S. during 2006 was the warmest on record and nearly identical to the previous record, set in 1998, scientists said today.
Based on preliminary data, the 2006 annual average temperature was 55 degrees Fahrenheit, which is 2.2 degrees above the 20th century mean and 0.07 degrees warmer than 1998 [chart].
An unusually warm December propelled 2006 to the record, according to researchers at NOAA's National Climatic Data Center in Asheville, N.C.
The finding is based on more than 1,200 U.S. Historical Climatology Network stations. The data, primarily from rural stations, have been adjusted to remove artificial effects of urbanization and station and instrument changes.
U.S. and global annual temperatures are now approximately 1 degrees Fahrenheit warmer than at the start of the 20th century, according to NOAA. The rate of warming has accelerated over the past 30 years, the agency reports, increasing globally since the mid-1970s at a rate approximately three times faster than the trend as seen over the entire past century.
The past nine years have all been among the 25 warmest years on record for the contiguous United States.
The warmth of 2006 can be blamed in part on an El Niño episode in the equatorial Pacific.
"A contributing factor to the unusually warm temperatures throughout 2006 also is the long-term warming trend, which has been linked to increases in greenhouse gases," according to a NOAA statement. "This has made warmer-than-average conditions more common in the U.S. and other parts of the world. It is unclear how much of the recent anomalous warmth was due to greenhouse-gas-induced warming and how much was due to the El Niño-related circulation pattern."
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