Eco Brief: New Study Ranks Recent Arctic Outbreak One of Coldest on Record!
A new World Weather Attribution study by the Princeton, NJ based Climate Central studied the recent late December, early January cold snap in the eastern US in the context of climate. What they found will not surprise anyone in the eastern USA. It was cold. Very cold! In fact when looking back on records that date back to 1880, a cold snap as cold as this has only happened 5 other times on record. The last winter with a colder two week period was 1981-82, nearly 36 years ago! And what may be more surprising is the other four colder 2 week periods occurred very early in the 20th century before the 1920s. So to say this was a rare event is an understatement.
But it goes a step further. The research also found that the coldest two weeks of winter have warmed greatly since the times of the industrial revolution. In fact the coldest two weeks of winter are now 4 degrees F warmer than they were a century ago (see first image in slideshow above). So that makes this climate snap that much more unlikely in terms of its relation to our current, warmer climate. In fact the study has a figure for that: This type of cold wave is now about 15 times more rare!
On the question of does climate change make these types of Arctic Outbreaks more likely, the team did not find any evidence of that. "In fact, the temperature of two-week cold waves has increased over all of North America, as expected in a warming world." The study says "We see no evidence of an increased intensity of these cold waves, but rather a faster warming than the mean winter temperature in northern North America."
But a study in September 2017 in the AMS Journal does find a link between a weaker Polar Vortex in recent decades and Eurasian cooling trends during winter. That study did not extend to the USA or Canada.
Based on the above evidence, one can conclude that more studies of cold air outbreaks on a warmer globe are needed! One possible caveat which needs to be studies more is: Are cold outbreaks likely to linger longer in a warmer climate because of a slowed jet stream or propensity for a more blocked pattern? Again more reason for more study!
The World Weather Attribution study research was performed by the World Weather Attribution team, a partnership of Climate Central, the University of Oxford Environmental Change Institute (Oxford ECI), the Royal Netherlands Meteorological Institute (KNMI), the University of Melbourne, and the Red Cross Red Crescent Climate Centre (the Climate Centre).
So then what is the theory of why a warmer climate may help bring about these strange, somewhat out of place cold snaps?
Well here's the theory. Every winter there is something called the Polar Vortex which spins around an extremely cold air mass over the North Pole. Sometimes a piece of the Polar Vortex breaks away and moves southward into the USA. It happens every winter, more or less. That brings cold air south. Over the past couple of decades the Arctic has been warming more than 2 times as fast as the rest of the planet because of Climate Change. This "may" have made the Polar Vortex more unstable. More accurately the warming may have made the "lasso-like" winds around the Polar Vortex, which typically corral the cold air inside, more unstable & weaker. These weaker winds (essentially a weaker jet stream) start to wobble more/ they undulate more/ they become more wave-y and big dips develop allowing all that cold air to surge south. In other words the cold air escapes its Arctic pen and gets displaced. You can see this progression in the images and animation contained inside the slide show above.
This time, for some unlucky folks, the cold air was displaced and lingered in the eastern USA. If you were inside this cold dome it certainly did not feel like Global Warming! In fact it felt more like an ice age setting in. BUT if you were able to see the weather on the rest of the Planet you would have seen that the majority of the planet was above normal. In fact the world as a whole was 1 degree F above normal as seen in the slide show above.
Enhancing this cold outbreak was a warm ridge of high pressure along the west coast of the USA. When it is cold in the east it is almost always warm along the west coast. This is a typical see-saw effect. But at least 2 new studies show that Climate Change is likely making that ridge gradually larger and stronger. A stronger ridge in the west would act to enhance the cold air in the east.
Watch my 4 minute video explanation of the theory below and how this cold snap may have spiked the bomb cyclone!
And lastly it is worth noting that a warmer Arctic likely means a slow down in the atmospheric river, the jet stream. The jet stream is fueled by a contrast of cold vs warm. If it is not as cold, the contrast is less and the winds tend to weaken. This type of pattern would lend itself to slower moving systems and at times, stalled, block-y patterns. In a warmer climate both high and low pressure systems may tend to linger more. And this would lead to drier droughts, wetter floods, longer heat waves and yes, perhaps longer cold snaps (but contrary to this recent cold snap, not typically colder, cold snaps).
This all leads back to one common theme. In a warmer climate expect more extremes (whatever they may be), expect the unexpected and at times expect the unprecedented!
Jeff Berardelli, Atmospheric Scientist & Eco Journalist