If the Polar Vortex is due to Global Warming, Why are U.S. Cold Waves Decreasing?

From Dr Roy Spencer

January 31st, 2019 by Roy W. Spencer, Ph. D.

It’s much easier to devise and promote a climate change theory than it is to falsify it. Falsification requires a lot of data over a long period of time, something we don’t usually have in climate research.

The “polar vortex” is the deep cyclonic flow around a cold air mass generally covering the Arctic, Canada, and Northern Asia during winter. It is irregularly shaped, following the far-northern land masses, unlike it’s stratospheric cousin, which is often quite symmetric and centered on the North and South Poles.

For as long as we have had weather records (extending back into the 1800s), lobes of cold air rotating generally from west to east around the polar vortex sometimes extend down into the U.S. causing wild winter weather and general unpleasantness.

We used to call this process “weather”. Now it’s called “climate change”.

When these cold air outbreaks continued to menace the United States even as global warming has caused global average temperatures to creep upward, an explanation had to be found. After all, snow was supposed to be a thing of the past by now.

Enter the theory that decreasing wintertime sea ice cover in the Arctic (down about 15% over the last 40 years) has tended to displace the polar vortex in the general direction of southern Canuckistan and Yankeeland.

In other words, as the theory goes, global warming sometimes causes colder winters. This is what makes global warming theory so marvelously adaptable — it can explain anything.

In the wake of the current cold wave, John Christy skated into my office this morning with a plot of U.S. winter cold waves since the late 1800s. He grouped the results by region, and examined cold waves lasting a minimum of 2 days at a station, and 5 days at a station. The results were basically the same.

As can be seen in the plot below, there is no evidence in the data supporting the claim that decreasing Arctic sea ice in recent decades is causing more frequent displacement of cold winter air masses into the eastern U.S., at least through the winter of 2017-18:

The trend is markedly downward in the most recent 40 years (since 1979) which is the earliest we have reliable measurements of Arctic sea ice from satellite microwave radiometers (my specialty).

Now, I suppose that Arctic sea ice decline could have some influence. But weather is immensely complex. Cause and effect is often difficult to ascertain.

At a minimum we should demand good observational support for any specific claim. In this case I would say that the connection between Eastern U.S. cold waves and Arctic sea ice is speculative, at best.

Just like most theories of climate change.