The hardest season to write about climate change is winter, because somewhere in the world there's cold air. Right now, that cold air is here in "Chiberia," where temperatures just went back into the positive digits after setting a record low on January 6th—16 degrees below zero.

So, no global warming… unless you live in sunny Highgate, Vermont, which set a high of 52 degrees Monday, ten degrees above the prior record. Bangor, Maine reached a high of 51. It was practically balmy along the Atlantic seaboard yesterday, far from the frozen tongue of Arctic air that's reaching well past Chicago and down into the Ozarks. Alaskan cities broke a number of record highs last month, which is nice if you don't have to rely on the permafrost to keep your house from tilting. California has been unusually hot and dry, with historically low snowpack totals. Overseas, Amsterdam hit a January high.

The culprit is the jet stream, which is drunk right now, writes Greg Laden. When the jet stream gets drunk, it slows down and starts to meander and wobble and end up in places it usually doesn't go. When it teeters and falls down into the mid-northern latitudes, it allows cold Arctic air to pour into the U.S.

Why? You're probably used to seeing the jet stream in two dimensions on television; understanding requires visualizing it in three dimensions, as in this video from Dr. Jennifer Francis, a climate scientist from Rutgers whose work focuses on the Arctic climate:

When temperatures go up in the Arctic—and it's been warming much faster than the latitudes below in recent years—the hill between the warmer air to the south and the cold air to the north becomes less steep. Like a river running out of the mountains into the plain, the jet stream meanders when it slows, in part because it becomes less powerful.

"It's more easily deflected by obstacles like mountains or domes of hot air," Francis says. "It has less 'oomph' to it."

Francis's work has focused on the "Arctic Amplification" in recent years, the feedback mechanisms that make the Arctic so vulnerable to warming. When sea ice declines, as it has precipitously over the past 20 years (with a rebound in 2013 to levels from a few years ago), sunlight is absorbed by the ocean instead of radiated back by the ice.

That you may be familiar with; it's paralleled by snow melt. But there's a third feedback mechanism. "The water vapor part gets a lot less press," Francis says. Less ice means more water vapor, which also retains heat; and when the water vapor condenses, it releases latent heat. "The action is sort of like a greenhouse gas, and it contributes to the rapid warming."

The science on this isn't settled yet; this video from the Yale Forum on Climate Change gives you a sense of where it stands. Kevin Trenberth, a senior researcher at the National Center on Atmospheric Research, questions whether the Arctic heat reservoir is big enough to create changes at a hemispheric level instead of a mere regional one.

And a specific event, like the cold snap that just buried the city, can't be traced specifically to climate change. As always, the relevant analogy is a famous one from climate scientist Dr. James Hansen: It's like steroids in baseball, which don't cause specific home runs, but can increase the likelihood that a player will hit more home runs over an extended period of time.

As the Arctic warms, Francis and others are keeping an eye out for more frequent drunken jet streams, bringing unexpected and often unwelcome weather at unfortunate times of the year. "The pattern of the jet stream is just the kind of thing we'd expect to see happen," Francis says.