There has been some stuff in the past 2 months that could be linked to erratic jet stream behaviour - which in turn could be influenced by Arctic sea ice loss - like a series of storms battering Europe's Northwest, such as the St. Jude storm at the end of October, followed in December by Xaver, Dirk and Erich. Or a huge part of Siberia being so anomalously not-cold that it helped November being the warmest on record globally.
Now we have this:
This funny image (though what it depicts isn't funny for people who live in the US) from Greg Laden's blog shows how a portion of the polar vortex has broken off and moved over to the US, bringing ultra-low temperatures and snow to the Midwest and Northeast. Just two weeks ago there was a winter heat wave on the US East Coast, now it's extremely cold, and who knows what' swings will follow in weeks to come.
Like Andrew Freedman wrote over at Climate Central a couple of days ago:
The cause of the Arctic outbreak can be traced to northeastern Canada and Greenland, where an area of high pressure and relatively mild temperatures is set to block the eastward progression of weather systems, like an offensive lineman protecting the quarterback from the other team.
Here's an animation of that high pressure area (that incidentally also causes something of a cracking event in the Beaufort Sea, but more on that later):
And while it's cold in the US, today Europe has had to deal with another one of these (hat-tip to Desdemona Despair):
Plenty of extreme weather to go round, although it's relatively warm here in Austria and records are broken in the Netherlands (should get colder in a week or so). As always, there's no direct link to anything, and so it could all just be one big coincidence. Until it isn't.
Expect More Frequent Extreme Cold (and Hot) Weather
Climate scientist and leading expert on Arctic climate change, Jennifer Francis, says that while she would not attribute the current cold that's gripping the US to global warming, it is consistent with what she expects from global warming. I spoke with Francis this weekend about the connections she sees between weather, the jet stream, and climate change.
In many respects “the jet stream really is what creates our weather” here in North America, she said, adding that there's a “very amplified pattern to the jet stream” right now, “meaning that it's taking these huge swings northward and southward. And whenever that happens is when we get these unusual warm and cold events anytime of the year.”
As an example of how a very amplified pattern can cause warm extremes, she pointed out that Finland is experiencing very warm weather for this time of year because of a big swing that has persisted in the jet there, but in the opposite direction as the one that's causing the North American cold outbreak.
Finnish news Yle reports “the exceptionally mild winter has persuaded many birds to stick around in Finland for longer than usual. Some small birds have even started to tweet spring songs.” In another story, they report that a “snow shortage” has driven ski vacationers away from the slopes and instead to the spas and swimming pools.
Francis said a certain frequency of very amplified jet stream occurrences is normal, but that global warming is causing the frequency to rise beyond normal. The main effect of an amplified jet stream pattern is to increase the occurrence of floods, droughts, heat waves, and, you guessed it: cold spells.¹
The driving mechanism behind the jet stream is the north-south air temperature gradient, and that gradient is being strongly impacted by what's called “Arctic amplification,” a consequence of global warming which is very much underway already. Shrinking Arctic sea ice, less snow cover on land in spring and summer, and more moisture in the air, to name just a few, are all primary consequences and feedbacks pushing the Arctic to warm even faster and thus to further amplify the jet stream pattern.
Read the rest here.
Francis’ research, however, is still disputed. Dr. Kevin E. Trenberth, a distinguished senior climate scientist at the National Center for Atmospheric Research, told ClimateProgress on Monday that he was skeptical of Francis’ assessment.
“Jennifer’s work shows a correlation, but correlation is not causation,” he cautioned. “In fact it is much more likely to work the other way around.”
Instead of Francis’ theory that a warm Arctic moves the jet stream, Trenberth said it could be that the jet stream moves, leading to a warmer Arctic. And Francis’ theory could work if the Arctic was, in fact, particularly warm and iceless — at the moment, in winter, the Arctic is cooler and icier.
“I am not saying there is no [climate change] influence, but in midwinter, the energy in these big storms is huge and the climate change influence is impossible to find statistically,” he said. “So we have to fall back on understanding the processes and mechanisms.”