What has scientists so stunned is how far above other hot years 2012 was. Nearly all of the previous 117 years of temperature records were bunched between 51 and 54 degrees, while 2012 was well above 55.

"A picture is emerging of a world with more extreme heat," said Andrew Dessler, a Texas A&M University climate scientist. "Not every year will be hot, but when heat waves do occur, the heat will be more extreme. People need to begin to prepare for that future."

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Online:

National Climatic Data Center summary of US weather in 2012, http://1.usa.gov/UHhwpx

NCDC chart showing 2012 versus other years, http://1.usa.gov/13eHTrJ

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Seth Borenstein can be followed at http://twitter.com/borenbears