Matt Rourke / AP file
People play in water from an open fire hydrant during the afternoon heat on July 18, 2012, in Philadelphia. July was the hottest month ever on record in the contiguous U.S.
By Elizabeth Chuck, NBC News
If you found yourself bundling up in scarves, hats, and long underwear less than usual last year, you weren't alone: 2012 was the warmest year on record in the contiguous United States, according to scientists with The?National Oceanic and Atmospheric Administration.
The average temperature for 2012 was 55.3 degrees Fahrenheit, 3.2 degrees above normal and a full degree higher than the previous warmest year recorded -- 1998?-- NOAA said in its report Tuesday. All 48 states in the contiguous U.S. had above-average annual temperatures last year, including 19 that broke annual records, from?Connecticut through Utah.
?We?re taking quite a large step,? said Jake Crouch, a climate scientist from the NOAA National Climatic Data Center, which has recorded temperatures in the contiguous U.S. for the past 118 years.
It was also a historic year for "extreme" weather, scientists with the federal agency said. With 11 disasters that surpassed $1 billion in losses, including Superstorm Sandy, Hurricane Isaac, and tornadoes across the Great Plains, Texas, and the Southeast and Ohio Valley, NOAA said 2012 was second only to 1998 in the agency's "extreme" weather index.
A long-term warming trend for the U.S., combined with drought and a northerly jet stream, led to the record heat, explained Crouch.?
"During the winter season, the jet stream tended to stay further north of the U.S.-Canadian border, so that limited colder outbreaks in the country. It also limited precipitation. So that led to a warm and dry winter season, and that persisted through the spring," he said.?
"That warm and dry spring and winter laid the groundwork for the drought we had this summer... . When we have drought, it tends to drive daytime temperatures upward."
The unprecedented warm weather wasn't contained to the United States.
A corresponding rise in global temperatures prompted the World Meteorological Organization to call the rate at which the Arctic sea ice was melting "alarming" in its?Nov. 28, 2012, report.
?The extent of Arctic sea ice reached a new record low. The alarming rate of its melt this year highlighted the far-reaching changes taking place on Earth?s oceans and biosphere. Climate change is taking place before our eyes and will continue to do so as a result of the concentrations of greenhouse gases in the atmosphere, which have risen constantly and again reached new records,??World Meteorological Organization?Secretary-General Michel Jarraud said.
Each year since 2001 has been among the warmest on record worldwide, with 2012 likely to "be no exception despite the cooling influence of La Ni?a early in the year," the report added.
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NOAA expects to have global data for 2012 sometime in the coming weeks, but Crouch said scientists already know with certainty "it's going to be in the top ten" warmest years ever.
Adding to the extremes: 2012 was the driest year on record for the U.S., with 26.57 inches of average precipitation -- 2.57 inches below average. Those dry conditions created an ideal environment for wildfires in the West, which charred 9.2 million acres -- the third highest amount ever recorded, NOAA said Tuesday.
Other notable climate activity from 2012:
- Snowpack totals across the Central and Southern Rockies were less than half normal.
- July was the hottest month ever on record in the contiguous U.S.
- Tornado activity was concentrated toward the beginning of the season, with large outbreaks in March and April in the Ohio Valley and Central Plains, but the final 2012 tornado count will likely be less than 1,000 -- the least since 2002. "The factors behind that are kind of related to what was going on with the drought. We didn't have these large storm systems moving through the country, so that limited precipitation, and that also limited severe weather outbreaks," Crouch said. What made this year so high on the extreme weather index were cyclones, hurricanes, and the heat, he said.
- Alaska was cooler and slightly wetter than average, and had a record-cold January. "Their January temperatures were 14 degrees below average. Many locations in Alaska had temperatures 30 degrees below zero," Crouch said, adding that Anchorage, Alaska, set a new snow record.
- Hawaii experienced growing drought conditions, with 47.4 percent of the state experiencing?moderate-to-exceptional drought at the beginning of 2012 and 63.3 percent at the end of the year. Alaska and Hawaii were not included in the bulk of NOAA's 2012 report because of terrain issues, and because scientists don't have records dating back as far as states in the contiguous U.S.
While NOAA made no meteorological forecasts for 2013, Crouch said the drought was going to continue to be an issue.
"The drought got a lot of attention this summer when it was having impacts on agriculture. More than 60 percent of the country is still in drought," he said. "And if things don't change, the drought is going to continue to be a big story in 2013."
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