Published: January 8th, 2013
By Andrew Freedman
It’s official: 2012 was the warmest year on record in the lower 48 states, as the country experienced blistering spring and summer heat, tinderbox fire weather conditions amid a widespread drought, and one of the worst storms to ever strike the Mid-Atlantic and Northeast.
According to the National Oceanic and Atmospheric Administration (NOAA), 2012 had an average temperature of 55.3°F, which eclipsed 1998, the previous record holder, by 1°F. That was just off Climate Central’s calculation in mid-December, which projected an expected value of 55.34°F, based on historical data.
The 1°F difference from 1998 is an unusually large margin, considering that annual temperature records are typically broken by just tenths of a degree Fahrenheit. In fact, the entire range between the coldest year on record, which occurred in 1917, and the previous record warm year of 1998 was just 4.2°F.
"Climate change has had a role in this [record],” said Jake Crouch, a climate scientist at NOAA's National Climatic Data Center in Asheville, N.C. He said it isn't clear yet how much of the temperature record was due to climate change compared to natural variability.
During the summer, nearly 100 million people experienced 10 or more days with temperatures greater than 100°F, which is about one-third of the nation’s population, NOAA reported.
With 34,008 daily high temperature records set or tied the year compared to just 6,664 daily record lows — a ratio of about five high temperature records for every one low temperature record — 2012 was no ordinary weather year in the U.S. It wasn’t just the high temperatures that set records, though. Overnight low temperatures were also extremely warm, and in a few cases the overnight low was so warm that it set a high temperature record, a rare feat.
Even more astonishing is the imbalance between all-time records. According to data from NOAA's National Climatic Data Center, there were 356 all-time high temperature records set or tied across the entire U.S. in 2012, compared to four all-time low temperature records. All of the all-time record lows occurred in Hawaii.
As the climate has warmed during the past several decades, there has been a growing imbalance between record daily high temperatures in the contiguous U.S. and record daily lows. A study published in 2009 found that rather than a 1-to-1 ratio, as would be expected if the climate were not warming, the ratio has been closer to 2-to-1 in favor of warm temperature records during the past decade (2000-2009). This finding cannot be explained by natural climate variability alone, the study found, and is instead consistent with global warming.
Driven largely by the warm temperatures and the massive drought, one measure of extreme weather conditions, known as the Climate Extremes Index, shows that it was the second-most extreme year on record, second only to 1998. Studies show that in response to global warming, some extreme events, such as heat waves, are already becoming more likely to occur and more intense.
The year was also characterized by extreme drought, and two states — Nebraska and Wyoming — also had their driest year on record. Eight more states had annual precipitation totals that ranked in the bottom 10.
At its maximum extent in July, drought conditions encompassed 61 percent of the nation, with the most intense conditions in the Great Plains, West, and Midwest.
According to NOAA, the year saw 11 natural disasters that cost at least $1 billion in losses, including Hurricane Sandy, which struck the Mid-Atlantic and Northeast on October 29-30.
Globally, 2012 is expected to be ranked as the eighth-warmest year on record, with that announcement coming later in the month.