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2015 U.S. Temperatures in Review

After a cold start to 2015 for the Eastern U.S., the year finished like a torch, boosting the U.S. 2015 temperature ranking all the way up to No. 2. During the peak of the cold in February, nationwide record low temperatures outnumbered record highs by nearly 2-to-1. But in December, the staggering heat flipped that ratio big time, with record highs outpacing record lows by an astounding 21-to-1. Overall, that forced the record highs to easily outnumber the record lows 2-to-1 for the year as a whole.

Taking a closer look, once February ended, the below-average temperatures quickly became a thing of the past. Spring was the 11th warmest and summer was the 12th hottest on record for the U.S. The warmth continued to build through the end of the year, giving the country its hottest fall on record and its hottest December on record. And while not all locations exhibited precisely the same temperature trends, for many U.S. cities, 2015 was one of their hottest 10 years on record.

When you zoom into the local scale, the story is more nuanced. The Western states were hot most of the year, only backing off toward normal in the last couple of months. Montana, Oregon, and Washington ended up finishing 2015 with their hottest year on record. Meanwhile, 2015’s cold start in the Northeast faded quickly, and the warmth started to dominate. Massachusetts and Pennsylvania had their 17th hottest year on record. New Jersey had its 11th hottest year on record. And Florida, despite its cool February, still had its hottest year on record.

From a global perspective, while the current El Niño gives temperatures a boost, the increase in greenhouse gases from the burning of fossil fuels is the primary driver of the overall 2015 global heat record. In fact, even the recent and relatively cooler La Niña years are warmer than the El Niño years from just 30 years ago.