More and more, we are learning that climate change can lead to some pretty strange and counterintuitive effects, especially when it comes to the wintertime.
For instance, scientists have pointed out for a number of years that warmer seas, and a wetter atmosphere, can actually fuel more snowfall in massive nor’easters affecting the U.S. East Coast.
More controversial still is an idea called “Warm Arctic, Cold Continents.” This is the notion that as the Arctic warms up faster than the middle latitudes, it may sometimes cause a displacement of the region’s still quite frigid air to places that aren’t so used to it. In other words, even as the planet warms, masses of cold air could also become more mobile and deliver quite a shock at times when outbreaks occur in more southerly latitudes.
In November and December of 2016, for instance, temperatures at the North Pole surged tens of degrees above normal while at the same time a huge mass of abnormally cold air descended over Siberia. In November, during one of the excursions, Siberian temperatures were “up to 60 degrees below normal.”
Now, a new study in the Bulletin of the American Meteorological Society makes the case that in January and February — later in the winter than those events — another, perhaps related change is occurring. This one involves the notorious “stratospheric polar vortex,” a loop of extremely cold and fast-flowing air, high in the atmosphere, that tightly encircles the Arctic in the freezing dark of polar winter. This vortex can sometimes develop bulges, allowing for a more southerly invasion of air.
The study, led by Marlene Kretschmer of the Potsdam Institute for Climate Impact Research in Germany, sought to find patterns in the stratospheric polar vortex over the past 37 years, categorizing its behavior into seven states, ranging from a tight loop around the Arctic to “a weak distorted vortex.”
And it determined that the stronger and more defined vortex has been occurring less frequently, while distorted states have been growing more common — a change linked to colder temperatures over Eurasia. “This study provides quite some evidence that the cooling trend over Eurasia was at least partly affected by the weakening of the stratospheric polar vortex,” Kretschmer said. She conducted the study with five colleagues from universities in Germany, the Netherlands and the United States.
The “polar vortex” is both a popularly known and deeply confused concept — the problem is that there are two of them, which sometimes interact. The stratospheric polar vortex is far higher in the atmosphere and forms a much tighter loop. Then there is a lower “tropospheric” version that more directly affects the weather we all experience.
The work also suggests there’s a role played by the loss of Arctic sea ice, a phenomenon linked to climate change. When floating sea ice melts north of the Eurasian continent, that can lead to a greater flux of heat from the ocean to the atmosphere as an icy cap on that warmth is removed.
In turn, that can lead to a cascade of atmospheric effects that ultimately weakens the stratospheric vortex, high above.
“It matches with this hypothesis that the Arctic does have an effect and that climate change, leading to a decrease in sea ice, has an effect on large scale circulation, in this case the stratosphere,” Kretschmer said.
Previous research by Kretschmer has found a link between low levels of sea ice in the Kara and Barents Seas, north of Russia, and broader atmospheric patterns.
Those living in the United States will instantly wonder how all of this applies to the extreme “polar vortex” event of the winter of 2014. But in fact, the new study finds stronger evidence of a “Warm Arctic, Cold Continents” pattern over Eurasia than it does over North America. Kretschmer said she believes more research is needed on how stratospheric disruptions in winter could affect North America, too.
This whole line of inquiry remains relatively novel in climate research, however, and the chains of causation are nothing if not complicated. Climate scientist Kevin Trenberth of the National Center for Atmospheric Research, for one, remains cautious about the work. In a comment on the new study for The Washington Post, Trenberth suggested that the picture is more complex and that Arctic changes aren’t the only thing going on — citing major trends in the Pacific and Atlantic oceans as well.
The new study presents “a number of quantities that are related to one another, but one can not say they are causal, as claimed,” Trenberth commented by email. “On the contrary, there is good evidence of other influences that play a major causal role. Thus the Arctic amplification goes along with and is consistent with profound changes in the stratospheric polar vortex in January and February, even as profound influences come into the region from lower latitudes.”
He’s not the only skeptic. A study published last year in the journal Geophysical Research Letters regarding the “Warm Arctic, Cold Continents” hypothesis rejected the idea that continental cooling was linked to the loss of Arctic sea ice.
“Whereas the directionality toward warming Arctic surface temperatures is well understood to be linked strongly with accelerating sea ice loss, there is neither an established theory nor strong experimental evidence that midlatitude temperature trends having opposite directionality results as a dynamical response,” found the authors, a team of researchers with the University of Colorado in Boulder and the National Oceanic and Atmospheric Administration.
As all of this suggests, even as some scientists suggest that the dramatic changes to the Arctic are reverberating in the latitudes where many of us live, others continue to point out that our weather also has well established and more traditional drivers, like the Pacific Ocean. And those are also changing. It’s a complicated picture with a lot of moving pieces — but the fastest-moving one, the Arctic, seems more than capable of delivering some surprises.