Sunday, September 24, 2017

One of the Most Bizarre Ideas About Climate Change Just Found More Evidence in Its Favor

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 both 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.  Capital Weather Gang reported that in November, during one of the excursions, Siberian temperatures were “up to 60 degrees below normal.”

Here’s what the configuration looked like last December:(Credit: Image obtained using Climate Reanalyzer, Climate Change Institute, University of Maine) Click to Enlarge.

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 outward 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,” said Kretschmer.

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.

Kretschmer provided this diagram to show how the two are situated and can interact:Strong stratospheric polar vortex / Weak stratospheric polar vortex (Credit: Marlene Kretschmer of the Potsdam Institute for Climate Impact Research) Click to Enlarge.

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.
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 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.”

Click to Enlarge.  One of the Most Bizarre Ideas About Climate Change Just Found More Evidence in Its Favor

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