This summer has brought intense heat to much of the Northern Hemisphere and severe wildfires – not only to the American West, but to places like Sweden. Heat waves, droughts and wildfires are all events that climate scientists say are becoming more frequent and severe as a result of human-caused global warming.
We know that warming doesn’t affect the whole globe evenly. The Arctic is warming at least twice as fast as the rest of the planet. And that extreme warming may be a major factor in our changing weather right here in New England.
One factor for the heat this summer is a reported “stalling” of the jet stream—the fast flowing, narrow, meandering air current that makes your flight from California to Boston faster than the other direction.
“The big north-south swings in the jet stream is actually the thing that stalled,” said Jennifer Francis, a research professor at Rutgers University. Francis has pioneered the science linking Arctic change to shifting weather patterns in North America.
“The reason that’s important is that it’s those north-south waves in the Jet Stream that create the highs and lows that we see on a weather map.”
When the jet stream gets stuck in one place, then the weather also gets stuck, she explained.
Another phenomenon that’s been happening more often is a splitting in two of the jet stream. One branch has been going north along the Arctic Ocean, the other branch goes southward across the middle of the continent.
That means the weather pattern between the jets don’t have anything to push them along, making the weather patterns more stagnant and persistent, Francis said.
So why is Sweden on fire? Same reason.
“It just so happens that there’s a big northward swing in the jet stream both over the western part of North America and over the western part of Europe,” she said. That means hot, dry weather is stuck over northern Europe. “That’s where we’re seeing the big heat waves and forest fires.”