2006 Was Warmest Year Yet Recorded for U.S.

Aalok Mehta
National Geographic News

January 10, 2007

Last year was the warmest year ever recorded in the United States,
continuing the trend of increasing temperatures brought about in large
part by human-produced greenhouse gases, a new government report says.

According to preliminary data from the National Climatic Data Center (NCDC) in Asheville, North Carolina, 2006's annual average temperature in the contiguous U.S. was 55°F (13°C)—the warmest since monitoring began in 1895.

That's 2.2°F (1.2°C) above the 20th century average and 0.07°F (0.04°C) warmer than 1998, the previous record holder.

The high temperatures contributed to a record U.S. wildfire season, deadly heat waves, and persistent severe droughts in a number of locations, along with many other climate anomalies. (Related: "Wildfire Forecast: More Devastating Seasons to Come for U.S." [September 19, 2006].)

According to NCDC, an unusually warm December tipped the scales.

Springlike conditions in much of the country made it the fourth warmest December on record, with five states experiencing their warmest Decembers and no state having temperatures below average, the NCDC report says.

The report adds that 2006 was the sixth warmest year globally, with temperatures 0.94°F (0.52°C) above average.

Human Cause?

Much of the 2006 warming can be attributed to a continuing El Niño, a periodic warming of the tropical Pacific Ocean off the northwest coast of South America that affects climate around the globe.

El Niño reduced the amount of Arctic air flowing into the U.S., the NCDC report says.

But last year's heat also continues a disturbing long-term trend of increasing temperatures.

"The past nine years have all been among the 25 warmest years on record for the contiguous U.S., a streak which is unprecedented in the historical record," the NCDC report says.

"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," the report adds. "This has made warmer-than-average conditions more common in the U.S. and other parts of the world."

Just how much each factor contributed to 2006's record temperatures is still unclear, the report says.

But the combination of El Niño and greenhouse gas buildup may heat things up for a while yet.

A forecast by climate scientists at the U.K. Met Office's Hadley Centre for Climate Change predicts that those conditions will combine to make 2007 the warmest year on record.

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