The Controversial Link Between Epic Storms and a Warming Arctic

The Controversial Link Between Epic Storms and a Warming Arctic
From Wired - March 13, 2018

Its that time of the year again, when massive winter storms lash the eastern United States and your uncle posts on Facebook about how it proves climate change is a hoax. After all, why would you still need a good coat on a warming planet?

The fallacy is, of course, that weather is not the same as climatethough the two are intertwined in sometimes surprising ways. And one controversial theory argues that weirdly enough, its a warming arctic thats causing extreme winter weather in the eastern US. A new study out today in Nature Communications purports to bolster that argument, but the idea has sharply divided climate scientists. Arguing aside, though, the debate might be great for public understanding of climate change.

The researchers monitored temperatures in the arctic and compared them to whats known as the Accumulated Winter Season Severity Index, which takes into account temperature and snowfall. Based on data from 12 cities, they found that when the arctic is warm, severe winter weather is two to four times more likely than when the arctic is cold.

That's a bit odd, given that climate researchers have traditionally looked toward the tropics as a driver of global weather. I think that's kind of this engrained dogma in the field, says MIT climatologist Judah Cohen, lead author of the paper. There's this maybe built in bias or prejudice that's skeptical of the role of the arctic, and I think that's played a big part in the controversy.

Now, this was an observational analysis, because its not like the researchers could tweak temperatures in the arctic and see how that affected weather in the US. So while they could show a correlation between activities in the two regions, they couldnt definitively demonstrate that a warming arctic is causing changes in weather down south. They admitted as much in the paper, but to help strengthen their argument, the researchers worked out a lag correlation": They looked at peaks in arctic temperatures and found that these anticipated severe weather by five days, which would suggest a link.

But not so fast, says climate scientist James Screen of the University of Exeter. In some of those locations, there does not appear to be any lag, and in others the indication seems to be weak. It's better than nothing, I guess, but it does not convince me, Screen says.

Again, just because two things are correlated doesnt mean theyre playing off each other. It could be that the arctic circulation and the US circulation are changing simultaneously, and there's just a bit of a lag between the changes in the circulation and this weather index, Screen adds. I would say it's suggestive, but it does not totally convince me.

But say a warming arctic is responsible for wacky winter weather in the United States. What could be driving it? One theory points to the jet stream. The arctic is of course cold, and the lands to the south of it are less so. That temperature difference between the cold arctic and the area farther south is one of the sources of energy that drives the winds of the jet stream, says Rutgers University climatologist Jennifer Francis, a co-author on the paper.

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