If you live in the Midwestern United States, you might have noticed last week was really cold.

Like, colder than some parts of Mars cold. Chicago, for example, dropped to a low of around minus 30 degrees Celsius and with the wind chill, it felt as low as minus 50.

Schools were closed, postal services were suspended, flights were cancelled. It got so bad that dozens of people died and many more lost toes and fingers to frostbite. Now, with all that cold, some people [not naming names here] have argued that this winter is evidence against global climate change.

Well, we're here to tell you that is, obviously just a bunch of hot air… or cold air or whatever I don't care anymore... The point is...there's actually growing evidence that a warming Arctic means colder winters. Now, first things first.

Climate is not the same as weather. Weather is what's happening in the atmosphere over a short period of time, while climate is long term patterns in weather. So just because it's particularly hot or cold one week doesn't necessarily mean that the climate is or isn't changing over years or decades.

But long term changes in the atmosphere can lead to more fluctuations in weather or extreme weather events like what we saw in the last couple weeks. To understand why, you have to understand what actually caused the sudden deep freeze. You've probably heard the term polar vortex being thrown around.

That's a large area of low pressure and cold air that hangs out near one of the Earth's poles. There are actually two polar vortexes—one at each pole. But the one in the North is the one that everyone is talking about because it's the one that.

Chicago can sometimes get enveloped by. It's usually kept in place by the polar jet stream— a fast moving river of air flowing in a counterclockwise direction high above the earth's surface. When the jet stream slows down— like it often does in winter— it becomes weaker and wobblier, and that can let the polar vortex poke down into parts of the northern hemisphere.

As frosty air moves southward, warm air from the equator moves northward. And that means some areas freeze their tuchuses off, while others are sweltering. Sled dog races, for example, had to be cancelled in Alaska because it was too warm.

And the Southeastern US has been dealing with a heatwave. This push and pull of air leading to extreme winter weather isn't a new thing. In fact, the term polar vortex is thought to have first be coined in 1853.

What is unusual is that these vortex-driven bouts of extreme weather are happening more often and lasting longer. And rather than being proof positive that global warming isn't a thing, that's actually entirely consistent with our understanding of a changing climate. Climate models predict that if the Arctic gets warmer, there will be less of a temperature difference between the air there and the air in mid-latitude regions those between the equator and the poles.

That temperature contrast is part of what fuels the winds, so less of a difference would mean slower winds high up in the atmosphere. And slower winds make the polar vortex less stable and the jetstream wavy-er, so this kind of extreme winter weather would be more likely. It also means such weather events would hang around longer, since the cold air isn't shoved back up North again as quickly.

And all that is exactly what we've seen happen. The Intergovernmental Panel on Climate Change reports that the Arctic is warming faster than anywhere else on the planet because of arctic amplification. Basically, when sea ice melts, it leaves larger patches of dark water that absorb sunlight better than the ice sheets, causing further warming.

And a 2015 paper published in Science showed that the speed of winds in the polar vortex have decreased by 4 to 6 percent in the past 35 years and the kinetic energy of those winds has gone down by 8 to 15 percent. This year, daily temperatures in the Arctic have been up to 20 degrees higher than average. And that undoubtedly made the vortex even more likely to move southward.

Also, we can see evidence for climate change all over the globe right now. While there were two record lows in January— both in Illinois—there were 35 record highs, mostly in Australia. Australia's average temperature exceeded 30 degrees last month.

And such record-setting isn't just happening this year. If you look back over the past decade, there have been a lot of records set, and a lot more record-setting hot days than cold ones, which is a pretty strong hint that our planet is warming overall. And I'd just like to point out that the US, though we think of it as very big and important is only around two percent of the earth's surface.

So no, a lot of ice and snow in one part of this one country does not refute climate change. In fact, this is kinda exactly what models predicted would happen. And those models suggest there's a lot more in store.

A 2016 paper in the journal Nature Climate Change found that the vortex has been getting weaker and shifting eastward towards Eurasia since the 1980s. That means in the future, it'll will likely dip down over the East Coast more often— and Europe, as well, is more likely to be hit by arctic-like blasts. But how often these extreme weather events happen, or how long they will last in the future, is of course still uncertain.

Weather is really hard to predict, and we need more data on just how climate change impacts the vortex and other features of our atmosphere. Still, it's probably pretty safe to say we haven't seen the last really bleak winter— or the last really scorching summer. Thanks for watching this episode of SciShow News!

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