It has been so warm in the United States this year, especially in March, that national records were not just broken, they were deep-fried.
Temperatures in the lower 48 states were 8.6 degrees above normal for March and 6 degrees higher than average for the first three months of the year, according to calculations by the National Oceanic and Atmospheric Administration. That far exceeds the old records.
The magnitude of how unusual the year has been in the U.S. has alarmed some meteorologists who have warned about global warming. One climate scientist said it is the weather equivalent of a baseball player on steroids, with old records obliterated.
“Everybody has this uneasy feeling. This is weird. This is not good,” said Jerry Meehl, a climate scientist who specializes in extreme weather at the National Center for Atmospheric Research in Boulder, Colo. “It’s a guilty pleasure. You’re out enjoying this nice March weather, but you know it’s not a good thing.”
It’s not just March.
“It’s been ongoing for several months,” said Jake Crouch, a climate scientist at NOAA’s National Climatic Data Center in Asheville, N.C.
Meteorologists say an unusual confluence of several weather patterns, including La Nina, was the direct cause of the warm start to 2012. While individual events cannot be blamed on global warming, Mr. Crouch said, this is like the extremes that are supposed to get more frequent because of man-made climate change. Greenhouse gases come from the burning of fossil fuels, such as coal and oil.
It is important to note that the unusual winter heat is mostly a North American phenomenon. Much of the rest of the Northern Hemisphere has been cold, said NOAA meteorologist Martin Hoerling.
The first quarter of 2012 broke the January-March record by 1.4 degrees. Usually records are broken by just one- or two-tenths of a degree. U.S. temperature records date from 1895.
The atypical heat goes back even further. The U.S. winter of 2010-2011 was slightly cooler than normal and one of the snowiest in recent years, but after that things started heating up. The summer of 2011 was the second-warmest summer on record.
The winter that just ended was the fourth-warmest on record. Since last April, it has been the hottest 12-month stretch on record, Mr. Crouch said.
But the month where the warmth turned especially weird in the United States was March.
Normally, March averages 42.5 degrees across the country. This year, the average was 51.1 degrees, which is closer to the average for April. Only one other time, in January 2006, was the country as a whole that much hotter than normal for an entire month.
The “icebox of America,” International Falls, Minn., saw temperatures in the 70s for five days in March, and there were only three days of below-zero temperatures all month.
In March, at least 7,775 weather stations across the nation broke daily high-temperature records, and an additional 7,517 broke records for night-time heat. Combined, that is more high-temperature records broken in one month than ever before, Mr. Crouch said.