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A pair of new climate studies suggest an intensification of strong storms called nor’easters and other disruptive extremes affecting the East Coast of North America on an overheated planet.
Nor’easters generally form within about 100 miles of the East Coast between North Carolina and Massachusetts, often when cooler air from Canada meets warm, moist air over Gulf Stream waters. Those contrasting air masses can start to spin with a nudge from the jet stream, fueling storms that can produce damaging winds, coastal flooding and intense, disruptive snowfall in the winter.
The strongest nor’easters are already significantly windier and rainer than they were in the middle of the 20th century, said University of Pennsylvania climate scientist Michael Mann, a coauthor of a study published on 14 July in the Proceedings of the National Academy of Sciences.
A 2022 study showed a similar trend of intensification for storms forming over the Atlantic and hitting Europe, and that the track of those storms is moving northward, potentially putting unsuspecting areas more at risk.
Mann said the increases in the intensity and precipitation rates of the strongest nor’easters have likely been fueled by increases in ocean temperatures and the increased moisture capacity of a warming atmosphere.
“There are two reasons to look at the most intense nor’easters,” Mann said via email. “First, from an impact standpoint, they do the most damage, including coastal erosion, destruction and paralyzing snowfalls. The 1962 Ash Wednesday storm, with 84 mile per hour gusts, is a great example. In today’s dollars, it did $21 billion worth of damage.”
And just last February, a classic nor’easter described at the time as a “bomb cyclone” dropped several feet of snow over parts of Virginia and North Carolina and caused damaging flooding along parts of the Massachusetts coast, Eastern Long Island, and the Jersey Shore.
Mann said the increases in the intensity and precipitation rates of the strongest nor’easters have likely been fueled by increases in ocean temperatures and the increased moisture capacity of a warming atmosphere.
The researchers tracked 900 nor’easters back to 1940 in combination with a careful reanalysis of historical climate conditions surrounding the storms, including notable events like the Perfect Storm in 1991, Storm of the Century in 1993, and Snowmaggedon in 2010.
In the very strongest storms, the wind speeds have increased about 5.4%, from 69 to 71 mph, “but since destructive potential goes as the wind speed cubed, that’s a roughly 17% increase in destructive potential,” Mann said.
Overall, he added, a lot of research suggests that extra warming in the Arctic, which reduces the temperature contrast between high latitudes and midlatitudes, will lead to less storminess overall, but the destructive potential of intensifying nor’easters warrants attention.
Compared to other types of storms, nor’easters feed more off the heat of the ocean, which remains considerable in winter, “So those storms that can make it past the obstacles to development have the potential to grow stronger than they otherwise would have,” he said. “While we don’t see any evidence of increased intensity for the ‘average’ nor’easter, the strongest ones are clearly getting stronger.”
“My interest in these storms, and how they’re being impacted by climate change has been inspired by two personal experiences,” he said, first noting the March 1993 “storm of the century,” which caused 270 deaths and $12.2 billion worth of damage across 26 states, according to the National Ocean and Atmospheric Administration.
Mann said the storm disrupted a spring break road trip in Florida, where the temperature in St. Augustine dropped from the 70s to 40s in a few hours.
“We drove past Okefenokee Swamp later that day and it was snowing,” Mann said. “Then we stopped off in Southern Georgia for the night and temperatures dropped to the mid 20s. We froze. I will never forget that.”
“The strongest nor’easters can have impacts comparable to category 1 and 2 hurricanes, with effects encompassing a larger area.”
He said he remembers another infamous nor’easter, Snowmaggedon, from February 2010 because a U.S. senator who rejects science that proves human-caused warming used the occasion to build what he called an igloo in an attempt to cast doubt on climate science. At the same time, Mann said he ended up stuck in a hotel room for three days with several feet of snow blocking most roads in Pennsylvania.
As such storms grow stronger in a warming world, said Anthony Broccoli, an atmospheric scientist at Rutgers University who was not involved in the new study but who also researches nor’easters, “it will be important to remember that the strongest nor’easters can have impacts comparable to category 1 and 2 hurricanes, with effects encompassing a larger area.”
With sea level rise accelerating along the East Coast, Broccoli added that nor’easters “will lead to greater coastal flooding even without any changes in storm intensity.”
The increased thermal energy from warming oceans is likely driving the trend toward stronger nor’easters, and there could be other large-scale changes to ocean currents and winds that could shift the tracks of nor’easters, potentially raising unexpected risks in new areas, he said.
The new research doesn’t mean that temperatures are getting colder, but that the frigid air that still does form over the Arctic in winter will still make its way south, showing up perhaps more frequently in unexpected regions, or with increased unusual seasonal extremes that can damage crops.
The Arctic Connection
Large-scale changes affecting nor’easters and cold weather extremes in the United States likely include accelerated warming of the Arctic region, climatologist Judah Cohen said in an email interview. Cohen, a visiting scientist at MIT and director of seasonal research with Atmospheric and Environmental Research, published an 11 July study in Science Advances that bolsters evidence for a climate connection.
Cohen said that, as far as he’s concerned, the new paper is “preaching to the choir,” because its conclusions are consistent with his own research showing that “Arctic change can lead to episodic increases in severe winter weather in the U.S. east of the Rockies including extreme cold and disruptive snowfalls.”
The temperature contrast between the Arctic and the midlatitudes is one of the main forces that creates key winds at different altitudes, like the jet stream and polar vortex, and moves weather systems around the Northern Hemisphere.
Cohen’s work over recent years suggests that accelerated warming of the Arctic “stretches” the polar vortex—like elongating a round rubber band—into positions that let cold polar air spill southward more frequently.
He noted that two of the most recent nor’easters specifically named in the new paper by Mann and his coauthors, in March 1993 and January 2018, occurred during stretched polar vortex events. The new paper, he said, “provides a medley of possible causes but doesn’t settle on any one cause.”
His own recent paper, he said, shows “for the first time that stretched polar vortex events are overwhelmingly associated with extreme cold and heavy snowfall in the Eastern U.S.,” compared to other polar vortex configurations.
Often the polar vortex flows in a tight coil around the North Pole, containing the Arctic air, but Cohen’s study, and other research, suggest a trend to more frequent stretched polar vortexes and the associated cold-air outbreaks and storm impacts. Taken altogether, he said the new research helps explain regional “winter cooling trends and an increased number of heavy snowfalls in the Eastern U.S. over the past two and a half decades.”
—Bob Berwyn (@bberwyn), Inside Climate News
