As anyone who follows certain presidents on Twitter knows, it’s counterintuitive: climate change is caused by global warming, but it’s terribly cold outside, and the cold spells seem to be getting more frequent. But yes, the changing polar vortex is due to climate change.
First, there is the difference between climate and weather. Weather is what we experience day to day, but climate is the larger, long-term, physical patterns that drive the weather. Any change to the climate can cause local fluctuations in weather, but weather and climate are not the same. I like to explain it to students using the old analogy: weather is whether you bring an umbrella to school; climate is whether you own an umbrella at all. You can also, under current circumstances, use “wearing snow boots” and “owning snow boots”.
So what about the polar vortex then? Well, the polar vortex is always there, usually sitting above the Arctic, keeping it cold for all the polar bears and walruses. The vortex is held in place by the jet stream, an atmospheric current which runs through the northern hemisphere. When the jet stream is strong, the polar vortex stays where it belongs. When the jet stream is weak, the jet stream can wiggle. And the polar vortex wiggles with it. (See illustration, thanks NOAA.)
Because the climate is getting warmer, the Arctic is warming faster than anywhere else on the Earth. The strength of the temperature difference between the Arctic and the rest of the Northern Hemisphere is one of the things that keeps the jet stream in place. Weaker temperature differential, weaker jet stream. So as the Arctic gets warmer, the jet stream gets weaker. And wigglier. And starts curving south where it didn’t before. The polar vortex, in turn, moves south. And that’s why we had to cancel school for two days to keep everyone from getting frostbite.