From The Mountain Town News (Allen Best):
The big winter in California—and, before that, four years of not much snow? The big and repeated snows in Boston several years ago?
They, along with many of other extreme weather events, might be joined at the hips with the melting ice in the Arctic Ocean. That’s the emerging evidence described on a webinar by Jennifer Francis of Rutgers University.
“There’s a ton of research that has been going on lately in regard to this issue of how the rapid melting and warming may or may not be connected to the extreme weather that has been going on around the globe,” she said in the session sponsored by the Metcalf Institute for Marine & Environmental Reporting.
The line of reasoning is that there has been an uptick in the number of extreme events. Some, such as Roger Pielke Jr. of the University of Colorado-Boulder, have disputed at least part of this evidence. They argue that more people are living in harm’s way, such as in beach-front locations vulnerable to hurricanes or along rivers, thus bloating the damages when storms do occur.
Francis, in her 30-minute talk, didn’t acknowledge that argument, but instead pointed to something called the “Arctic amplification” beginning in about the mid-1990s. She acknowledged some difficulty with defining extreme weather events. “It’s a very hard to get robust statistics on these changes. The atmosphere is a very noisy place,” she said.
But the extreme events like the drought in the Sierra and the snow in Boston do have something in common: They’re caused by “stuck” weather patterns.
“This I where the Arctic may be playing a role,” she said.
Temperature increases have been well documented. “Globally, we’re on the edge of a 1.5 degree Centigrade increase in year-to-year anomalies compared to the 1881-1981 baseline. “We are in a very disturbing situation here. We are getting warmer and warmer, and we are already bumping up against the 1.5 degrees that the Paris agreement set as a limit.”
This warming has been particularly evident in the Arctic. It has been warming two to three times more rapidly than the rest of the globe. At times, and not just summer, it has had temperatures as warm as those of New York City. In summer, the ice has ebbed at a pace far more rapid than the losses predicted by climate models.
The summer ebb of sea ice is also wildly out of proportion to the ebbs and flows during the last 1,450 years as documented by the study of sediments on the bottom of the Arctic Ocean.
“There are lots of ups and downs, little wiggles, but it’s been pretty steady up until modern times,” she said.
In late March, scientists with the National Snow & Ice Data Center reported that air temperatures lat autumn and winter had been 2.5 degrees Celsius (4.5 degrees Fahrenheit) above average over the Arctic Ocean. The overall warmth was punctuated by a series of extreme winter heat waves over the Arctic Ocean, continuing the pattern also seen in the winter of 2015. This, they say, contributed to a record minimum winter ice advance.
“I have been looking at Arctic weather patterns for 35 years and have never seen anything close to what we’ve experienced these past two winters,” said Mark Serreze, the NSIDC director, said in a March release.
“We are clearly in uncharted territory,” said Francis in the webinar this week.
As the ice melts, white is replaced by the dark blue of the open ocean. Instead of solar radiation being reflected, it’s being absorbed. This, in turn, helps heat the atmosphere even more.
But there’s also this confusing fact: as the Arctic warms, there can be unusual cold in the eastern United States and parts of Asia. The mid-latitudes overall have been warming very slowly as compared to the Arctic.
This is explained by the Arctic amplification. It disrupts the fast-moving river of high-altitude air called the jet stream. The jet stream creates our weather as it moves across North America. Instead of a straight line, thought, it tends toward greater meandering or waviness.
Now scientists are starting to use a new word, sinuosity, which is a metric of how wavy the jet stream becomes. The greater the sinuosity, the greater the waviness. This increased waviness, in turn, results in persistence of weather patterns, such as the snow and cold of Boston and the dry ground of December in the Sierra Nevada.
Francis cautioned that not all extreme weather can be directly linked to the warming of the Arctic and the shifting of the jet stream. But there is a link reflected in the number of extreme weather events.
“Weather patterns really are changing, but they are affected by so many things,” she said: storm tracks, the jet stream, planetary waves. “It’s a really very complicated story, but we really are starting to get a handle on some of these mechanisms.”
I’d like to have asked her whether snow in Denver less than two weeks before Memorial Day had anything to do with the disappearing Arctic sea ice, but the webinar ended.
If you want a deeper dive into this subject, I recommend an interview with Francis conducted last December by Yale e360. It’s longer but a very easy read. And here’s 5-plus minute video clip that graphically presents the jet stream component.