Expect more frequent extreme cold (and hot) weather

By agreenerlifeagreenerworld on January 29, 2014 • ( 1 Comment )

By guest contributor Matt Owens

Climate scientist and leading expert on Arctic climate change, Jennifer Francis, says that while she would not attribute the recent cold that griped 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.

As we barrel forward with fossil fuel consumption, these trends will continue. And because of the inertia built into the climate system, even if we halted emissions now, Francis said that there would continue to be significant ongoing change. Of course, if we stay the course, that change will happen faster.

Within the Arctic, an additional effect of climate change is that sea ice is becoming increasingly mobile (it used to be mostly locked into a continuous ice pack every season). That means the oil platforms in and near the Arctic Ocean will have to be alert for incoming ice that the winds or storms have pushed around.

These changes in the Arctic – and with climate change elsewhere – are dramatic. Considering how everything is physically connected by this layer of gas we call an atmosphere, I think we can see this cold spell as a greeting from the Arctic north, telling us that even with global warming, we’re still going to have winters for a long time to come, and they may just become colder for many of us,² even if our summers become hotter too.

Image at top of page from SFSU jet stream analysis; images below from the Climate Change Institute’s Climate Reanalyzer.