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The season’s first surge of Arctic air made its way into the northern reaches of the continental U.S. this week, and it will spread eastward for the weekend. But it’s just a taste of what’s to come.
A more intense surge of truly polar air will move in next week. Some of the coldest air in the northern hemisphere — yes, associated with the polar vortex — will move across southern Canada. As a result, much of the U.S. will be the coldest so far this season during the second half of next week.
In the U.S., very cold air doesn’t just appear. It has to arrive from somewhere, and that somewhere is generally the Arctic. When winds at both ground level and the level of the jet stream line up, they can drive Arctic chill southward, sometimes as far as the Gulf Coast and Florida.
A report from Climate Central’s World Weather Attribution team analyzed the current cold air outbreak for signs of a climate change signal, indicating:
The cold air outbreak of the next few days is nothing unusual, and neither inconsistent with an overall picture of a warming world, nor evidence that global warming is making cold weather more extreme. Such cold air outbreaks are, in fact, decreasing in intensity both in observations and climate models primarily because the source of the cold air, the Arctic, is warming strongly.
Bitterly cold air in the Lower 48 originates from the Arctic regions of Canada, Alaska, and sometimes Siberia. Earlier this week — even as Alaska is having its warmest year on record — temperatures began to plummet as Siberian air migrated east. But even in Alaska, the intensity of the recent cold did not set records.
Fairbanks had a chilly three-day stretch from Dec. 3-5. Over that time, overnight lows dipped as low as -36°F, beyond frigid for most of us but still 20°F above record lows for this time of year.
On the Alaskan shore of the Arctic Ocean, Barrow ended a run of 205 consecutive days above 0°F on Nov. 9. Of Barrow’s 10 longest stretches of temperatures above 0°F, eight of them have happened since 2000.
The cold currently moving into the Lower 48 has been a shift from the balmy autumn, but it hasn’t widely set records either. Denver came close, though, dropping to -10°F Thursday morning, but the record of -14°F — set in 1919 — held.
To be fair, a record did fall in Casper, Wyo. Thursday morning, when the temperature bottomed at -31°F, besting the old record for the date of -29°F. There could still be a few other cold records to fall this week as well. However, the ratio of record highs to record lows in the U.S. has been increasing over the past four decades as the planet warms. Record highs are outnumbering record lows 2-to-1 in the decade of the 2010s.
And the chill this week comes after a blistering November when daily record highs outpaced record lows by a stunning 48-to-1, the largest differential ever recorded in a month. It was also the second-warmest November on record, all but solidifying that 2016 will be the second-warmest year the U.S. has ever recorded.
It may seem counterintuitive, but cold outbreaks will continue to occur in a warming world. Over the course of decades, however, the frequency and intensity of those cold outbreaks is expected to decrease. A recent study found, for example, that if heat-trapping greenhouse gases aren’t curtailed, the ratio of record highs to record lows could reach 15-to-1 by the end of the century.
Historical perspective on temperatures and how we perceive them is important, too. What feels bitterly cold today is closer to past averages before climate change started to heat things up.
No question there will still be cold outbreaks during winter, even in a warming world. But slowly and methodically, and possibly without many people even noticing, the coldest of the cold will fade, and people may forget how cold it used to get.