As the Philadelphia region finally recovers from three nor'easters in two weeks, a new study suggests the harsh, frigid winter we've experienced on the East Coast is linked to a warming Arctic.

A peer-reviewed study published Tuesday in the journal Nature Communications says data show a strong relationship between record heat in the Arctic and weather extremes, including cold spells and heavy snow, in other parts of the U.S. The highest correlation was seen in Eastern states.

Previous studies have made similar suggestions based on a few months of data for particular years, but this study looked at a much larger data set from 1950 through 2016.

"In a nutshell, it's basically a study that provides some really solid evidence that connects this crazy warming we're seeing in the Arctic to the really bizarre weather further down in the U.S.," said study coauthor Jennifer Francis, a research professor with the department of marine and coastal sciences at Rutgers University in New Brunswick.

Francis and her coauthors, Judah Cohen and Karl Pfeiffer, both with Atmospheric and Environmental Research, a private contractor that works with government agencies such as NOAA and NASA, analyzed temperature anomalies and weather severity as well as daily weather in the middle latitudes of the U.S. They looked at weather data from 24 cities as geographically diverse as Seattle, Chicago, Atlanta, New York, and Des Moines, Iowa, over 66 years.

The correlation also extends into Europe, which has seen one of its harshest winters in years.

To derive their data, the researchers also took a deep dive into atmospheric pressure. They found winter is more severe in the East when the pressure was weak between the troposphere and stratosphere — more than seven miles up from sea level. That has been the hallmark of warming Arctic conditions and "warm air intrusion" this year.

Francis said much of that disruption is because of the jet stream — a swift-moving current of air six to nine miles above Earth's surface. The jet stream creates a sort of border with cold air on its northern side and warm air on its southern side. Normally, it runs in a fairly straightforward path, often staying north of us.

NOAA

But, as temperatures off the West Coast coincide with the retreat of sea ice in the Arctic, a pattern emerges.

The jet stream is energized by differences in temperature. Ultimately, the jet stream weakens when the differences between north and south are less. The jet stream then gets deflected, Francis suspects. As a result, its path becomes wavier and plunges south — meaning that cold air moves with it. That pattern remains in place for an extended period of time because it is easily deflected by things such as mountains and ocean temperatures.

So warmer weather up north creates trouble down south.  For example, if the jet stream dips below Philadelphia, the city experiences frigid temperatures later in the winter season.

Scientists around the world became alarmed Feb. 25 when an Arctic weather station recorded above-freezing temperatures for about 24 hours — a time of year when almost no sun is reaching the ground.  One monitor in Greenland recorded temperatures more than 50 degrees above normal in February. The scientists say the Arctic is warming at a rate two to three times faster than the global average.

The researchers note that, as the Arctic has warmed, heavy snowfalls in the East — with nicknames such as Snowpocalypse and Snowmageddon — have increased since 1990.

Francis, who studied meteorology and earned her Ph.D. in atmospheric sciences, said three-quarters of Arctic ice volume has disappeared in the last 40 years.  She attributes that to climate change caused by the burning of fossil fuels.

"That's a very key change in a very short amount of time," Francis said. "So these vicious cycles are getting stronger because the ice that floats on the Arctic Ocean is so thin now.  That tends to allow the jet stream to sag southward in these big dips. It's plunged as far south as Sarasota, Fla., where they had snow and iguanas freezing in the trees."

However, Francis is cautious in directly linking one specific weather event, such as a nor'easter, to conditions in the Arctic. Rather, she said, it fits a pattern.

"It's the kind of thing we expect to see more often," Francis said. "The jet stream causes these storms, so anything that affects the jet stream affects us."

While other scientists generally agree that climate change is helping foster wacky weather, they don't always agree on why.  And, Francis and her coauthors note the study has its limitations because it is based on observations of data and can't determine a direct cause and effect. They say more research is needed.