By CHRISTOPHER STEPHENS

(Anderson) Herald Bulletin

ANDERSON — Even for Hoosiers who are used to jokes that we can expect to experience all four seasons in the stretch of a week, this extreme wintry cold to early autumn swing is remarkable.

But these types of dramatic temperature changes are something Midwesterners should expect to experience much more often as climate change disrupts the traditional patterns of weather across the world.

The recent extreme cold, sometimes so frigid that frostbite can form within minutes, was caused by a dip in the polar vortex far more southerly than normal.

A polar vortex is an area of low pressure — a wide expanse of swirling cold air — that is parked in polar regions, as the U.S. Department of National Oceanic and Atmospheric Administration, or NOAA, explains it.

Sometimes this low-pressure system, full of cold Arctic air, can break off and migrate southward, bringing subzero winds and weather with it.

And while the NOAA explains this has always happened, several new studies suggest climate warming may be disrupting the pressure systems that keep it in check. And that could mean more extreme, though short-lived, bursts of extreme winter weather.

According to a study published by leading climate researcher Marlene Kretschmer at the Potsdam Institute for Climate Impact Research, over the last 37 years the frequency of weak vortex states in mid- to late winter has increased, which was accompanied by subsequent cold extremes.

Kretschmer attributes this to an increased frequency in a weak El Nino, another annual weather system that brings heavy rains in the summer.

So if climate change is supposed to make the world warmer, why is winter also getting worse?

“I’ve been making that argument that winter is shortening, but you’re getting these more intensive periods in that shorter winter,” said Judah Cohen, a climatologist at Atmospheric and Environmental Research.

Essentially, while climate change, an unnatural rise in global temperatures over time due to an increase in heat-trapping greenhouse gasses in the planet’s atmosphere, does in fact increase the average temperature year over year — it means shorter but much harsher winters.

To understand the cause-and-effect relationship it’s important to understand what usually keeps the polar vortex in check.

The term polar vortex refers to circular bands of winds near the poles that are strongest in wintertime and well above the jet stream in the stratosphere several miles above the surface of the earth.

Usually, those circular bands act as walls, but every so often, the winds break down and allow the cold air to escape.

And while climate change is warming the earth, not all parts of the earth are warming at the same rate; the Arctic is warming at a rate twice as fast as the world average, according to several climatologists including Deke Arndt, a scientist with NOAA.

“This Arctic amplification is driven by a handful of factors; the largest of these is the retreat of seasonal snow and ice. As the white stuff goes away, it exposes darker surfaces and land cover underneath which this introduces an additional warming effect across the region,” said Arndt.

In the last century, according to NOAA data, the nation’s average winter temperature has increased at nearly double the rate of that of the average summer temperature at 2 degrees in winter versus 1.1 degrees in summer.

And while that change doesn’t mean winter is likely to go away any time soon, it does signal a series of much milder winters that will faster erode the weather systems keeping cold where it belongs. And that will mean more winters like last week — when a mild winter is interrupted by an extreme, and extremely quick, cold spell.

“It’s quite possible the winter will average warm for December through February,” wrote Bob Henson, a meteorologist with the forecasting service Weather Underground in a blog post. “But that may well manifest as the extreme warmth we’ve seen over the last month followed by some much colder and colder than average conditions into February.”

Why am I sick when weather changes suddenly?

When the weather switches from cold to warm and back to cold again it seems like it’s a recipe for a cold.

But while quick changes in temperature seem to bring sickness with them, cold itself doesn’t actually make people sick — instead it’s just that germs tend to thrive in the cold but not frigid temperatures. Couple that with being trapped inside for long periods of time where sneezes and coughs can linger and it’s a recipe for sickness, according to Harvard Health.

So while it’s not directly the cause of sniffles and colds, that’s microbes like rhinoviruses and cornoavirsues — the two agents that typically cause the common cold — that idea that cold causes colds is somewhat rooted in science.