The recent cold snap has destroyed low temperature records in the West. In parts of Montana it hasn’t been this frigid since the ‘70s, grape growers in California have been anxious about their vines freezing, homeless shelters have been filling up, and in Oregon it's been so cold that even a geothermal bathing pool had to close. That’s right, it was too cold even for hot water.
Perhaps now you’re wondering: Why has it been so darned bone-chilling? The answer to that question has roots in the Arctic, and points to why people in the Lower 48 have a stake in the climate of the Far North.
The West’s recent Arctic stay-cation has come courtesy of the polar jet stream, whose high-altitude winds are responsible for many daily weather conditions. The jet stream often keeps cold air barricaded around Canada and Alaska, but in early December a lobe of the jet stream began dipping south from the Arctic, clearing the way for frigid air to spill into the Western U.S, and pushing warm air into the Arctic. If you imagine the jet stream as a racetrack of wind around the North Pole, lately its had an unusually big, loopy curve that dropped it into the southwest (for a general idea of what it looks like, see the cool NASA animation of the jet stream later in this story).
In contrast, during the winter of 2012, the jet stream didn’t meander as much, keeping cold air penned in up north. That locked Alaskans in an icebox, with temperatures there averaging minus 35 F in late January. (Apparently, the shape of car tires seems to change from round to square -- their bottoms flatten out -- at minus 45 F.
But now we’ve been freezing our butts off in the Intermountain West (and now the East Coast), and parts of Alaska are seeing record high temperatures. Last Sunday, it was a balmy 39 F on the north coast’s Prudhoe Bay.
This flip-flop isn’t outside the realm of “natural” up-and-down swings in climate. But there’s also a scientific debate under way about how Arctic warming will alter natural climate circulations, and how that could make severe weather in the Lower 48 more likely. “There will be other scientists who will say we can chalk this up to natural climate variability,” says Chuck Greene, a Cornell University earth scientist. Since you can’t link any single weather event, like the current cold snap, to climate change, that’s valid, he says; but “we are stacking the deck in favor of these kinds of conditions.”
That’s because the Arctic is heating up twice as fast as the rest of the Northern Hemisphere, and it’s hard to imagine all that heat entering the atmosphere won’t affect climate cycles, like the Arctic Oscillation. The Arctic Oscillation describes changes in atmospheric pressure at the North Pole, which shape the jet stream’s path and determine if it's fast and strong, or meandering and slow like a lazy river. When the circulation is strong, polar air stays trapped up north, turning car tires to squares. When it is weak, the jet stream creeps to the South, letting icy air escape into the Lower 48. The same process was behind the 2011-2012 deadly cold snap in Europe.
Since the Arctic Oscillation is quite unpredictable, and because it can override or complicate other weather-making patterns, it’s often called a weather “wild card.” Climate change could make it even wilder. The idea is that extra warmth in the Arctic narrows the temperature difference between high and mid-latitudes, which leads to the weaker, wobbly version of the jet stream that lets polar air travel south. Some scientists are starting to link loss of Arctic sea ice to snowy and cold winters in the U.S. and Europe, along with jet stream behaviors that resemble the wobbly version of the Arctic Oscillation.
Last year, a separate group of researchers also found evidence connecting Arctic warming to a slower-moving and wavier jet stream. That means weather, whether it’s drought, heat waves, rain, or cold spells, sticks around longer, stacking the deck in favor of extreme events. Some of the same scientists just published a paper in Nature Climate Change linking Arctic warming to extreme summer heat events in North America, Europe, and Asia.
That current cold spell looks consistent with that slowing, says Greene.
But as Climate Central reported earlier this week, the impacts of Arctic warming outside of the Arctic are still scientifically controversial, in part because the physical connections between Arctic warming and extreme weather haven’t been nailed down, some conflicting studies have come out, and some researchers think they need to accumulate more evidence, and more years of data, before drawing conclusions. It’s an active field of research, with lots more to learn.
But if the long arm of the jet stream is going to reach down more frequently, that has big implications for the West’s weather.
As a former under secretary at the National Oceanic and Atmospheric Administration, Jane Lubchenco, said last year: “What happens in the Arctic doesn’t always stay in the Arctic.”
Sarah Jane Keller is an editorial fellow at High Country News. She tweets @sjanekeller