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| Green Mountain Power released this image of tree damage in Vermont after last week's superstorm cut power to much of the state. Is climate change making these extreme winter storms more likely? |
Blizzard and winter storm warnings covered parts or all of at least 17 states. More than half the Lower 48 was below zero. It sleeted in Melbourne, Florida on Christmas Day. So much for climate change, right?
Or not. There's a case to be made that climate change made last week's weather situation worse than it otherwise would have. Climate change doesn't only make things warmer. Often and under the right conditions, it can just make things more extreme.
That said, here's a caveat with this storm: There's no proof climate change had anything to do with this, at least not yet. Scientists will probably study this huge, rambling system to learn if there was any connection. We can say there are consistencies with this storm and it's accompanying Arctic outbreak and climate change.
First of all, climate change does not cancel winter. Sure, winters are warmer than they used to be. But for most of the United States, it's easily still often cold enough in our now balmier winters to have snow.
Also, pretty much every winter storm that has ever existed needed warm air to survive. Low pressure systems in the winter pull warmth and moisture from places like the Gulf of Mexico or the warm Atlantic waters off the southeastern coast.
This warm, wet air encounters the usual cold air that exists in winter. That air is forced to rise up and over that colder air. Rising air cools and condenses, and unleashes a literal blizzard of snowflakes. This is just basic physics.
Under climate change, that warm, moist air is even toastier than it used to be decades ago. The warmer the air, the more moisture it can hold. More moisture more often than not means more precipitation. So it follows that winter storms can produce heavier snow than they used to. They have more moisture to deal with, so they can make more snowflakes than storms did decades ago.
In last week's storm, however most places didn't have extreme amounts of snow, with the exception of places blasted by lake effect snows around the Great Lakes.
The storm was certainly huge, both in how strong and big it was. Honestly, the storm was the largest in size that I can remember. This giant tempest was also able to pull down a rapidly advancing Arctic air mass that had its origins in Siberia.
If you want a big Arctic outbreak and/or a big storm, you want a wildly meandering jet stream. No piddling mini southward excursions or wimpy northward turns here! If the jet stream has a big plunge southward, it'll pull frigid Arctic air southward from near the poles.
Then, if that big plunge turns a corner at the bottom and heads back northward, you probably have a big storm on your hands
One reason the storm was able to get so big was an enormous dip in the jet stream deep into the heart of the nation. Then, the jet stream took a corresponding northward sweep up the East Coast and well into eastern Canada.
Whether the jet stream can meander like crazy in the winter frequently depends on the polar vortex. The polar vortex, you remember, is that giant swirl of frigid air that's usually somewhere in or near the Arctic all winter.
If the polar vortex is well north, and tightly wound, the truly frigid air stays up by the Arctic circle where it belongs.
If the polar vortex weakens, it can get pulled, elongated and/or migrated south toward the mid-latitudes of Asia, Europe or North America. The polar vortex can even break up into pieces temporarily.
When all this happens, trouble usually follow. It makes the jet stream meander all over the place and somebody gets a big Arctic blast and probably a nasty winter storm.
The jet stream depends upon a nice big contrast in temperatures between the Arctic and points further south. Such a contrast helps the jet stream "know its place" and not meander too much. The contrast probably encourages the polar vortex to keep its act together and not get weird or have a breakdown.
Here's the controversy: We know the Arctic is warming faster than the mid-latitudes, where most of us live. There's not as much of a contrast between, say, Houston and Whitehorse as there used to be. This diminished contrast might be encouraging the jet stream to meander, with bigger dips southward and bigger bulges northward.
Bigger dips and bulges in general mean bigger, more powerful storms, and more wild Arctic outbreaks in the winter.
Additionally, the Arctic warming might be messing with the Polar Vortex, that tightly wound core of super cold air that always hangs out in the far north during the winter.
Increasingly, it seems, this tightly wound vortex that would keep the coldest air above the Arctic circle gets oblong and oddly shaped, allowing the cold air to plunge south occasionally. Is climate change causing this?
As the Washington Post reports, the science isn't settled yet on whether the warming Arctic is creating more havoc with the jet stream, allowing these episodes of frigid air to blast into the United States, periodically.
It'll take years of more observation and study to really see if there's a connection between the warming at the top of the world and these weird cold blast in otherwise relatively warm years.
However, as Jennifer Francis, seniors scientist at the Woodwell Climate Research Center tells the Washington Post: "We've see the same situation basically the last three years in a row.....Here we go again."
So we have anecdotal indications that climate change can paradoxically give us these huge winter storms and Arctic outbreaks.
This is obviously bad news. As of Monday morning, the death toll for last week's superstorm in the U.S. had risen to 46. It'll probably go up more. This death toll is one of many sad consequences of a stormier, weirder weather world brought to us by climate change
Even if it is indeed true that we'll have to endure more winter superstorms like the one we just had, overall winters are clearly warming.
True to form, long range forecasts starting later this week and going through the first week of January call for above normal temperatures for most of the nation.
A week or two of relatively balmy weather in the middle of winter does nothing to prove or disprove climate change, but it is consistent with what we've been seeing in recent winters with the aftermath of these cold blasts and winter storms.
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