Record-breaking frosty temperatures, ice and heavy snowfalls have gripped huge areas of the Northern Hemisphere this winter. For example, cities in East Asia such as Beijing and Seoul shivered in two of the coldest snaps either had experienced for decades, over in Europe. Spain experienced record low temperatures of -25 Celsius and much of the Netherlands froze over, while snowstorms smothered the northeastern US with more than half a metre of snow.

This extreme weather, impacting more than a billion people worldwide, is yet another sign of the climate crisis despite the fact it looks like global cooling rather than global warming.  How so? Well, it’s got a lot to do with a warming Arctic prompting the collapse of the polar vortex. Does that all sound a bit complicated? Never fear, we will explain exactly what a polar vortex is, how it’s affecting our weather and linked to the climate crisis, and what we can do about it.

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Japanese rock garden after an ice storm in winter.
© Shutterstock

So, what’s a polar vortex then?

The polar vortex is a giant swirling ring of cold air that rotates high up in the atmosphere at both the North and the South Poles, but for this blog, we will focus on the polar vortex in the North Pole. It always exists near the poles, but weakens in summer and strengthens in winter. Being cut off from the sun’s warmth in the Arctic makes it very much colder than the equator, which stays hot year-round.

The atmosphere tries to balance that extreme temperature difference by setting the cold air in the North Pole spinning – and that’s the polar vortex. This giant spiral of freezing winds is in the stratosphere, at least 16km above the Earth’s surface, so it’s too high to directly affect our weather, but it does have an indirect impact. When it’s rotating nicely, all that cold air stays in the vortex, but when the vortex gets wobbly, that cold air escapes southward and starts a chain reaction that sends the temperature dropping. 

NASA’s Atmospheric Infrared Sounder (AIRS) instrument captures a polar vortex moving from Central Canada into the U.S. Midwest from Jan. 20-29.
© NASA

What makes the polar vortex go ‘wobbly’?

It’s a bit hard to unravel, but meteorologists think it’s got something to do with a sudden temperature spike in the air in the stratosphere above the North Pole. A rapid and extreme rise in temperature there tips the swirling polar vortex off its axis, and it starts to wobble and extends much further south than it usually does. During this wobbling, the cold air – also known as jet stream – is also pushed southwards. 

Early this year, weakened polar vortex brought record-breaking cold waves across East Asia. Now the vortex warped into two “legs” that protruded into North America and Europe. Those legs caused the frigid air closer to the earth’s surface (which is what directly affects our weather) to bulge southwards, forcing cold front down across much of Europe and North America this winter.

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