2012 Hottest Year On Record For Lower 48 States, NOAA Confirms

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.

The year consisted of the fourth-warmest winter, the warmest spring, second-warmest summer, and a warmer-than-average fall. With an average temperature that was 3.6°F above average, July became the hottest month ever recorded in the contiguous U.S. The average springtime temperature in the lower 48 was so far above the 1901-2000 average — 5.2°F, to be exact — that the country set a record for the largest temperature departure for any season on record.

"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 exactly how much of the temperature record was due to climate change compared to natural variability, but that it's unlikely such a record would have occurred without the long-term warming trend caused in large part by emissions of greenhouse gases.

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 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.

Nineteen states had their warmest year on record in 2012, mainly in the Plains and Midwest, where summer heat and drought was the most intense. An additional 26 states had one of their top 10 warmest years on record. Remarkably, every state in the lower 48 experienced an above-average annual temperature.

The extreme heat is even more vivid when examined at the local level. Cities such as New York, Boston, Washington, Milwaukee, St. Louis, Denver, Des Moines, and Chicago all set records for their warmest year.

Marquette, Mich., which is well-known for its cold and snowy winters, not only set a record for the warmest year, but also set a record for the most amount of days above freezing (32°F) in a single year, with 293 such days, and the number of consecutive days above freezing, with 237.

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