If you live in the eastern half of North America, you may have noticed that it’s cold outside, and not just because it's winter. While much of December has been unusually warm, these past few days have seen temperatures drop to the point where hot water spontaneously turns into snow when thrown.
So why is it so cold? It may seem like an easy joke to make a pun about global warming, but actually increasing temperatures are partly to blame. Of course sometimes it justgets cold in winter, but a lot of the extreme weather the Northeast is experiencing right now has to do with climate change.
As the Arctic—and the rest of the globe—gets warmer, these changing temperatures can have an effect on the jet stream, the band of air that travels west to east, typically near the U.S. border with Canada. Normally, it acts like a barrier, keeping cold Arctic air trapped in the northern latitudes and away from most of the people on the East Coast. At least, in theory.
In practice, a warming Arctic strains the jet stream’s ability to keep all that cold polar air locked away in the north. When the jet stream falters, that polar air can make its way south, sometimes as far as the Gulf Coast. And over the next week or so, that’s exactly what’s going to happen. Take a look at these air pressure maps of North America:
These maps show that air from the far north of Canada is flowing south into the American Midwest and Northeast, which is why it’s so cold outside right now. Normally the jet stream keeps that air confined to Canada, but thanks to climate change it's taking a hard right after passing the Rockies and heading south almost to the Gulf Coast.
So if you’re stuck outside on the East Coast this week freezing your extremities off, you can thank global warming.