Depending on who you are and what you’re into, Earth isn’t particularly habitable. OK, sure, if you’re some kind of polyextremophile microorganism, the world is your oyster. Even oysters are your oyster. You can manage temperatures down to -10 degrees and up to 250 degrees, high salt levels, no light, and a local pH—a measurement of acidity—of zero. That is sour. But then, if you’re a polyextremophile microorganism, you’re probably not a reader. No offense.

If you’re a human, though? Over 70 percent of the planet is basically off limits without serious technological support, because you can’t breathe underwater. Get much higher than 8,000 feet and you won’t be able to breathe as well as you might like; people have lived for years at 19,500 feet, but they probably didn’t enjoy it. And temperature? Extended periods above 95 degrees or just a few minutes below -130 and you’re dead. We humans are, in a sense, polyextremophobic. So maybe that’s why it’s so existentially dreadful for the heart of the United States to be hunkered down under temperatures as low as -65 (with the wind chill, you betcha) at the same time as Australia is pushing up toward 120. That’s a 185-degree difference, and too much of an overlap with the average lows and highs on Mars for any loyal Earthling to be happy with.

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So what the, you might ask, hell is going on? “We live on an interesting planet,” says Gerald Meehl, a climatologist at the National Center for Atmospheric Research. In 2004, Meehl and Claudia Tebaldi predicted that climate change would lead to worse, more frequent heat waves; turns out they were right. In the Northern Hemisphere, you can usually blame heat waves on a “persistent high,” which isn’t as much fun as it sounds—it’s a stationary blob of high-pressure air that diverts the jetstream and keeps cooler air from the pole from mixing with the warm air on the equator side. The warm air stays. Over Australia, persistent highs don’t block the jetstream, but they still cause heat waves by pulling in hot air from the continent’s deserts. Corals bleach, fruit bats die by the tens of thousands, roads bubble, railways buckle.

It’s even worse after a drought. Normally, a heat wave evaporates water from the ground, and that evaporation brings some cooling. But when there’s no more water, the heat has nowhere to go, like a pot on a flame after all the sauce has boiled away. And then when the temperature drops at night, the air’s ability to hold moisture goes down and the humidity goes up, making it harder for people to sleep. Oh, plus: wildfires. “You get multiple punches from climate change,” says Camilo Mora, a climate researcher at the University of Hawaii. “We fail to realize that many of these things are connected.”

Meanwhile, there’s a polar vortex. Or rather, there isn’t—typically the polar vortex is a whirl of low-pressure air in the stratosphere, 10 to 20 miles over the North Pole, contained by a fast-moving ribbon of wind. But sometimes warmer air can sneak up there. The winds invert, flipping backward from their usual west-to-east flow. “The cold air kind of pinches and stretches into two daughter1 vortices,” says Judah Cohen, a climatologist with Atmospheric and Environmental Research. “One piece goes to Eurasia and one to North America, and each piece brings cold air.”

So ... normal? It happens every two or three years, yeah, says Cohen. “But these kinds of polar vortex disruptions are happening more frequently than they used to,” he says. Blame the melting ice caps. Sea ice is a very good insulator, it turns out, acting like a sort of thermal cap on the warmer ocean below it. As sea ice in the Arctic melts (thanks to, yes, climate change), it stops insulating. “You peel away the ice and all of that heat transfers, because heat likes to go down-gradient, from hot to cold,” Cohen says. That warmer air flows upward, making the jetstream wavier and more energetic. And a wavy jetstream is what messes up the polar vortex.