Perhaps the best analogy yet for the insane cold weather now afflicting the US came from
science blogger Greg Laden, who created the viral image above. "Go home, Arctic," it reads. "You're drunk."
When it comes to the reason why the United States is currently
experiencing life-threatening cold—with temperatures in the negative-20s
in the Upper Midwest, and wind chills much lower than that—that's
actually not so far from the truth. "It's basically the jet stream on a
drunken path going around the Northern Hemisphere," explains Rutgers
University climate scientist
Jennifer Francis.
In other words, we're experiencing record-breaking cold temperatures
because a wavy and elongated jet stream has allowed frigid Arctic air to
travel much farther south than usual.
And according to Francis' research—which has drawn increasing
attention in the past few years—we're seeing more of just this kind of
jet stream behavior, thanks, at least in part, to the rapid warming of
the Arctic.*
To understand how it works, it first helps to think of the jet stream
as a river of air that flows from west to east in the Northern
Hemisphere, bringing with it much of our weather. Its motion—sometimes
in a relatively straight path, sometimes in a more loopy one—is driven
by a difference in temperatures between the equator and the north pole.
Southern temperatures are of course warmer, and because warm air takes
up more space than cold air, this leads to taller columns of air in the
atmosphere. "If you were sitting on top of a layer of atmosphere and you
were in DC, looking northward, it would be like looking down a hill,
because it's warmer where you are," explains Francis.
The jet stream then flows "downhill," so to speak, in a northward
direction. But it's also bent by the rotation of the Earth, leading to
its continual wavy, eastward motion.
As the Arctic rapidly heats up, however, there's less of a
temperature difference between the equator and the poles, and the
downhill slope in the atmosphere is accordingly less steep. This creates
a weaker jet stream, a jet stream that meanders more or, if you prefer
the new analogy, staggers around drunkenly. "As the Arctic continues to
warm, we expect the jet stream to take these wild swings northward and
southward more often," says Francis. "And when it does, that's when we
get these particularly wild temperature and precipitation patterns, and
they tend to stay in place a long time." (For a more thorough
explanation,
see here.)
That's not to say the jet stream never staggered around drunkenly in
the past. It did. But Francis thinks this is happening more often, and
the result is all manner of weather extremes, including both cold snaps
and also record heat. (Not every scientist agrees; for the debate over
Francis's work, see
here.)
Thus, it is not at all nuts to draw a connection between extreme
weather, including extreme winter weather, and climate change. In fact,
what would be truly stunning would be if the dramatic warming of the
Arctic were
not affecting the weather.
* This sentence was updated to reflect Francis's view that Arctic
warming may not be the sole cause of these jet stream patterns.
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