This week, temperatures are expected to hit historic lows across much of North America. Already, it has snowed in Texas and frozen in Tennessee, and hundreds of towns and cities are preparing for icy cold weather.

This week’s cold snap isn’t exactly unseasonal—after all, it’s autumn, heading toward winter, and it’s the time of year when much of North America sinks into chilly weather.

Some scientists think, though, that the frequency and intensity of these kinds of cold interludes may be changing as the planet warms, as counterintuitive as that might sound.

“This Arctic outbreak is connected to the behavior of the jet stream and the polar vortex,” says Judah Cohen, an atmospheric scientist at MIT. And those, in turn, are