Why it's been so cold in Calgary for a while now, and the climate change connection

The last couple of weeks have been brutally cold in the Calgary area, with temperatures dipping down to the –30s, with wind chills much colder, and extreme cold warnings by Environment Canada.

Why so cold for so long?

A senior scientist at the Woodwell Climate Research Center in Falmouth, Mass., says it was the jet stream all along.

"All of our weather is really governed by the jet stream and what the jet stream is doing," Jennifer Francis told The Homestretch this week.

"This is a fast-moving river of wind that encircles the northern hemisphere. It tends to be stronger in the wintertime but it controls whether it's cold or hot or rainy or dry everywhere around the Northern Hemisphere."

It's all connected

And that jet stream can really make things interesting.

"The jet stream has been in a very persistent pattern for the last couple of weeks. When the jet stream is south of you, it means the Arctic air to the north has no boundaries. It can come right down and spend time right there in Calgary," Francis said.

"It's all connected, too, to the persistent storminess along the West Coast. The high, record temperatures that have been happening in the southeast U.S., and even the tornadoes and storms striking the middle of the country, including the incredible situation happening in Colorado, where they have gone from unusual heat to extreme cold and snow."

Francis says research in the last five or so years has sharpened the connection between climate change and persistent weather patterns.

"With changes in the jet stream creating more persistent patterns means when you get a cold spell like this, it will probably last longer, but next winter it might be very different," she said.

"It's the persistence, not the cold itself, that people should focus on when we are talking about how climate change is having an impact."

Polar vortex

So how does a polar vortex fit in here?

"It resides much higher up in the atmosphere than the jet stream does, but it has similarities. The polar vortex is a pool of very cold air that sits, pretty much, over the Arctic Ocean but much higher in the atmosphere, about 30 miles (48 kilometres) high, and it's encircled by very strong westerly winds," Francis explained.

A polar vortex exists only during the winter and has little effect on weather.

"But every once in a while, instead of being circular, it can get disrupted. It can stretch out more like a kidney bean shape or even split up into a couple of different swirls of cold air," she said.

"When that happens, we see some wild winter weather."

With files from The Homestretch