Extreme weather events, like flooding in New Jersey after Superstorm Sandy,… (Mario Tama, Getty Images )
Last year was the hottest year on record for the contiguous 48 states, marked by near-record numbers of extreme weather events such as drought, wildfire, tornadoes and storms, according to the National Oceanic and Atmospheric Administration.
In its annual report, State of the Climate, NOAA reported that the average annual temperature was 55.3 degrees — 3.3 degrees greater than the average temperature for the 20th century. It was also a full degree higher than the previous record-high temperature, set in 1998 — the biggest margin between two record-high temperatures to date.
The report confirmed what many Americans may have suspected over the last year: that extreme weather events are becoming more common. The only year when there were more extreme weather events was 1998, largely because a greater number of tropical cyclones made landfall, NOAA researchers said.
In 2012, the Upper Midwest was hit with floods, the mid-Atlantic with sudden summertime storms, the West with wildfire and the Northeast with Hurricane Sandy, among many other events. Most of the country even now remains in the grip of drought.
For years, climatologists have been reluctant to draw a line from climate change to specific weather events, and the NOAA authors of the report were cautious about making links. But a growing body of research has begun to indicate that climate change creates conditions for the kinds of temperatures and events the United States experienced last year.
"We expect to see a continued trend of big heat events, we expect to see big rain events, and with slightly less confidence, we expect to see continued trend in drought," said Deke Arndt, chief of the climate monitoring branch, NOAA's National Climatic Data Center. "This is consistent with what we would expect in a warming world."
The NOAA report arrives amid demands from environmentalists and allies of President Obama that he take significant steps to address climate change. Although in his first term his administration increased vehicle fuel economy standards and drew up rules to reduce greenhouse gas emissions from new power plants, Obama's long silence on climate change rankled many backers.
"The facts speak for themselves — whether it is NOAA's announcement today that 2012 was the hottest year on record or the devastation caused by Superstorm Sandy," said Sen. Barbara Boxer (D-Calif.), chairwoman of the Environment and Public Works Committee.
Last year follows a decade that was the hottest since temperature recording began 133 years ago, NOAA said. Since 1895, as industrialization spread and the world began to burn more carbon-based fuels, the average temperature of the Lower 48 states has risen 0.13 of a degree each decade.
NOAA's report on average global temperatures, which is expected soon, is likely to show that 2012 was the eighth-hottest year on record around the world.
Last year's data showed that there were 356 record-high temperatures recorded around the country, and only four record lows, all in Hawaii. Three or four decades ago, the numbers of record highs and record lows were far more similar, said Richard Rood, professor of atmospheric, oceanic and space sciences at the University of Michigan and a writer for the blog Weather Underground.