As if things aren’t stressful enough right now, the weather is going wild. Temperatures in Boston last Wednesday soared to the balmy high-60s, cities across New England broke records for daily high temperatures, and the sun stayed out all day.
You know what happened next: On Thursday, the skies turned gray and temperatures dropped 30 degrees.
On Friday, the cold temperatures stuck around, and a winter storm moved in, bringing snow and sleet.
How did we so quickly go from T-shirt weather to pulling out the snow shovels? Some naturally occurring weather patterns are responsible, but climate change could be making them more intense.
A big reason for last week’s wild shifts in weather is the jet stream: a band of strong east-to-west winds that direct and energize weather systems. The jet stream forms between cold air in the north and warm air in the south; when air of two different temperatures meets, the warm air rises while the cool air sinks, creating winds.
Right now, the temperatures south of the jet stream are unusually warm, while temperatures in the north are downright frigid. Those extreme temperatures supercharge the jet stream, causing its winds to behave erratically. As they bend and kink, they shove cool air from the north downward and push warm air from the south upward.
“When kinks in the jet stream ripple through ... this boundary between cold and warm air can cross our area quickly, causing weather whiplash,” said Jennifer Francis, acting deputy director at the Woodwell Climate Research Center in Woods Hole.
Imagine tying one end of a jump rope up to a tree, then snapping the other side up and down hard to create fast waves. In the jet stream, those kinks are what create storms, and are what’s responsible for quickly pushing cold or hot air into a region.
This kind of weather whiplash is not unheard of in New England, which is situated between cold Canadian air and the warm air from the Gulf stream.
“[The] sharp contrast in temperatures ... can easily invade when a kink in the jet stream comes along,” said Francis.
But these rapid, dramatic shifts from unseasonably warm to unusually cold could be becoming more common and more severe because of climate change, which is making temperature extremes more common and could be having a rippling effect on the jet stream.
“Some evidence indicates that the atmosphere may become more ‘wavy’ and thus these sorts of temperature swings could occur more often,” said Adam Schlosser, senior research scientist at the MIT Center for Global Change Science.
Temperature snaps in the region this winter have also been caused by changes in the polar vortex, a large region of cold, spinning air surrounding both of Earth’s poles. Sometimes, that spinning air can affect weather in places far from the poles.
“The polar vortex ... sometimes becomes stretched from its normally circular shape into an oblong or can even be split into two,” said Francis. “When this happens, extreme winter cold spells usually occur, too.”
This phenomenon contributed to last month’s blizzard, and it’s a factor in the cold temperatures the region is seeing right now. While the polar vortex disruption caused a big southward dip in the jet stream this week, bringing in colder air, smaller kinks in the jet stream rippled warm and cool air through as well, making temperatures more erratic.
“Little waves riding along a big wave, like wind waves riding over an ocean swell,” Francis said.
Research suggests that as the Arctic heats up and melts due to climate change, these disruptions in the polar vortex are happening more often.
Wild swings in weather can be harmful to wildlife. False spring-like temperatures can confuse leaf and tree buds, causing them to flower too early and then die in frosty temperatures soon after. It may also throw off animals’ internal clocks that tell them when to eat, mate, and migrate.
There’s also some evidence that these oscillations are bad for human health. In 2018, a group of cardiology researchers linked extreme day-to-day shifts in temperatures to a significant increase in heart attacks. So these rapid shifts might be not just disorienting but dangerous.