Updated Wednesday, January 9, 2013 at 02:35 PM
The numbers are in: 2012, the year of a surreal March heat wave, a severe drought in the corn belt and a massive storm that caused broad devastation in the mid-Atlantic states, turns out to have been the hottest year recorded in the contiguous United States.
How hot was it? The temperature differences between years are usually measured in fractions of a degree, but last year’s 55.3 degrees blew away the previous record, set in 1998, by a full degree Fahrenheit.
If that does not sound sufficiently impressive, consider that 34,008 daily high records were set at U.S. weather stations, compared with only 6,664 record lows, according to a count maintained by Weather Channel meteorologist Guy Walton, using federal temperature records.
That ratio, which was roughly in balance as recently as the 1970s, has been out of whack for decades as the country has warmed, but never by as much as it was last year.
“The heat was remarkable,” said Jake Crouch, a scientist with the National Climatic Data Center in Asheville, N.C., which released the official climate compilation Tuesday. “It was prolonged. That we beat the record by one degree is quite a big deal.”
Scientists said that natural variability almost certainly played a role in last year’s extreme heat and drought. But many of them expressed doubt that such a striking record would have been set without the backdrop of global warming caused by the human release of greenhouse gases. And they warned that 2012 was likely a foretaste of things to come, as continuing warming makes heat extremes more likely.
Even so, the last year’s U.S. record is not expected to translate into a global temperature record when figures are released in coming weeks. The year featured a La Niña weather pattern, which tends to cool the global climate overall, and scientists expect it to be the world’s eighth- or ninth-warmest year on record.
Assuming that prediction holds up, it will mean that the 10 warmest years on record all fell within the past 15 years, a measure of how much the planet has warmed.
Last year’s weather in the United States began with an unusually warm winter, with relatively little snow across much of the country, followed by a March that was so hot that trees burst into bloom and swimming pools opened early. The soil dried out in the March heat, helping to set the stage for a drought that peaked during the warmest July on record.
The drought engulfed 61 percent of the nation, killed corn and soybean crops and sent prices spiraling.
In addition to being the warmest year, 2012 turned out to be the second-worst on a measure called the Climate Extremes Index, surpassed only by 1998.
Experts are still counting, but so far 11 disasters in 2012 have exceeded a threshold of $1 billion in damages, including several tornado outbreaks; Hurricane Isaac, which hit the Gulf Coast in August; and, late in the year, Hurricane Sandy, which caused damage likely to exceed $60 billion in nearly half the states, primarily in the mid-Atlantic region.
Among those big disasters was one bearing a label many people had never heard before: the derecho, a line of severe, fast-moving thunderstorms that struck central and eastern parts of the country starting June 29, killing more than 20 people, toppling trees and knocking out power for millions of households.
By the numbers
Average annual temperature: 55.32 degrees passed the old record of 54.32 degrees, set in 1998.
Number of states that had their warmest year: 19.
Number of people who experienced at least 10 days of 100-degree heat: 99.1 million.
Number of consecutive months that the United States had warmer than average temperatures: 16.
The Associated Press
SPENCER PLATT / GETTY IMAGES
A group of tourists look up at a building along Broadway during warm weather on July 6, 2012 in New york City.
SPENCER PLATT / GETTY IMAGES
A man pushes a cart of bottled water down Broadway during warm weather on July 6, 2012 in New york City.
SCOTT OLSON / GETTY IMAGES
Corn plants struggle to survive in a drought-stricken farm field on July 19, 2012 near Oakton, Indiana.