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Back in 2012, two researchers with a particular interest in the Arctic, Rutgers’ Jennifer Francis and the University of Wisconsin-Madison’s Stephen Vavrus, published a paper called “Evidence linking Arctic amplification to extreme weather in mid-latitudes.” In it, they suggested that the fact that the Arctic is warming so rapidly is leading to an unexpected but profound effect on the weather where the vast majority of Americans live – a change that, if their theory is correct, may have something to do with the extreme winter weather the US has seen lately.

In their paper, Francis and Vavrus suggested that a rapidly warming Arctic should interfere with the jet stream, the river of air high above us that flows eastward around the northern hemisphere and brings with it our weather. Sometimes, the jet stream flows relatively directly from west to east; but other times, it takes long, wavy loops, as in the image above. And according to Francis and Vavrus, Arctic warming should make the jet stream more wavy and loopy on average – some have called it “drunk” – with dramatic weather consequences.

Here’s the atmospheric physics behind the idea: Warm air expands, and naturally there is much more warm air at the equator than at the poles. Thus, the atmosphere is thicker at the equator, and the jet stream’s motion is driven by the decline in atmospheric thickness as one moves in a poleward direction – in effect, its atmospheric river flows “downhill,” in Francis’s words. However, if the Arctic is warming faster than the mid-latitudes, then the difference in thickness as you move in a poleward direction should decrease. And this should slow the jet stream, leading to more loops and turns – and consequently, weather of all types getting stuck in place for longer. There’s a nice video explanation of this by Francis here:

According to Francis, the extreme US winter of last year and now, the extremes at the beginning of this season, fit her theory. “This winter looks a whole lot like last winter, it’s a very amplified jet stream pattern,” she says. “We know that when we get these patterns, it tends to be very persistent. And it is definitely the type of pattern that we expect to see more often as the Artic continues to warm so fast.”………..

You can’t call Francis’s idea fully established. You can’t say there’s a “scientific consensus” on it. And you can’t say that the august UN Intergovernmental Panel on Climate Change embraces it. Not yet. But it’s certainly a very serious idea and one of the most discussed theories in climate science. Call it a contender. And if it’s right, well … then we all know, already, what global warming feels like.

Read more: http://www.smh.com.au/environment/climate-change/theres-growing-evidence-that-global-warming-is-driving-crazy-winters-20141122-11rq9v.html#ixzz3K1NykOCj