70-Degree Days in December: What?

Is climate change to blame for the Eastern United States’s warm spell?

A man exercises in Manhattan during an unseasonably warm December Sunday. (Lucas Jackson / Reuters)

Man, it’s a warm one.

At least, here in the eastern half of the United States it is. Since late last week, cities from Chicago to Atlanta to Boston have experienced decidedly un-seasonal heat, with temperatures dozens of degrees Fahrenheit above average. Here in D.C., we had our hottest December 12th since 1889. In Lexington, Kentucky, they did us one better, breaking a record set during the Grant administration.

As pleasant as this weather can be—if it doesn’t quite feel like Christmas in July, it’s at least like Hanukkah in April—the warmth can also provoke unease. Both memory and pop culture instruct that we should hope for a snowy Christmas, not a drizzly one. Sunny, clear days; 70-degree breezes: This is not what December is supposed to feel like around these parts. Something feels deeply wrong.

Alexis Madrigal, an Atlantic contributing editor, coined a term for such weather: “climate changey.” Scientists repeat that few individual weather events can be linked to climate change, and yet, how can an iced-coffee Advent be normal? Surveying an unprecedented California heatwave, historic flooding in South Carolina, and a strange and perplexing sandstorm in Tel Aviv, he wrote in October: “We need a word that reflects the basic anxiety of not knowing what the weather means anymore.” Climate changey is that phrase.

In Madrigal’s telling, climate changey stands in for both the weather event and the mental state. In the 2010s, even when weird weather is enjoyable, it feels like a planetary memento mori. Say goodbye to that white Christmas—more of this is coming, and also, by the way, you may die in it.

An odd byproduct of writing and reporting about global warming and ocean acidification is that you’re forced to conserve your anxiety. The whole thing is so worrying (despite the recent Paris agreement) that it doesn’t make sense to freak out over a stretch of nice days. And that’s especially true when there’s a scientific basis for not connecting this warmth to global warming.

Which is to say: Despite how climate changey these warm days feel, they’re almost certainly the product of El Niño, not global warming.

El Niño is a phase in the Pacific Ocean’s multi-year cycle. During El Niño, warmer surface waters collect in the ocean’s tropical and eastern half. (That is: The water off the western coasts of Central America—and thousands of miles beyond that, into the open sea—is much, much warmer than usual.) A band of low pressure forms over these warm waters. This week, that persistent low pressure has bumped the Jet Stream much further north than usual, sending subtropical air toward the Eastern United States.

This year’s El Niño is one of the strongest ever: Last month, meteorologists ruled it “too big to fail.” It’s helped bring cool rains to California, tempering that state’s long drought; it also played a role in the massive Indonesia fires in September and October and the imminent drought in the Horn of Africa.

Again, scientists haven’t connected the strength of this El Niño to climate change, so you should feel free to enjoy the warmth, despite the climate-changey vibes. But a recent study indicated that global warming is likely to bring more mega El Niños like this one.

Here in the East, it’s looking like we’ll have a warm, not a white, Christmas. So perhaps as you go out for your unorthodox Boxing Day jog, think back to 2010. That year, we experienced the Pacific Ocean’s other major phase, La Niña, which is when warm waters pool in its western half. And while El Niño can bring snow, too—in fact, some meteorologists think we’re in for major storms in February of next year—La Niña of 2010 did not fail to deliver: A post-Christmas blizzard carried more than a foot of snow to many of the same towns that have their windows open right now.

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