The strongest nor’easters — destructive and often deadly storms that slap the US East Coast with paralyzing rain, snow and flooding — are being supercharged by the effects of climate pollution, a new study found.
Nor’easters, which typically form between September and April, are fueled by the temperature contrast between cold Arctic air from the north and warmer, moist air from the Atlantic Ocean.
They are a huge threat to densely populated cities along the East Coast. The past decades have been peppered with nor’easters so devastating, some are now known by nicknames which sound like disaster movie titles.
The “Storm of the Century” in March 1993 was one of the deadliest and costliest ever recorded. It packed more than 100 mph winds, dumped almost 60 inches of snow in some places and killed more than 200 people.
“Snowmageddon” in 2010 unleashed more than 20 inches of snow on parts of Pennsylvania, Maryland, Virginia and West Virginia, killing 41 people and leaving hundreds of thousands without power.
Michael Mann, a climate scientist at the University of Pennsylvania and an author of the study, was trapped in a Philadelphia hotel room for three days during Snowmageddon. It was this experience that first sparked his curiosity about how these storms might be affected by global warming.
Fifteen years later he believes he has some answers.
There is a general consensus there will be fewer nor’easters in a warmer world, because the Arctic is heating up faster than the rest of the Northern Hemisphere meaning there is less of a temperature contrast to fuel the storms.
But what has been unclear is what will happen to the intensity of these storms, which have tended to be understudied, Mann said.
To answer this question, the scientists used historical data and a cyclone tracking algorithm to analyze nor’easters between 1940 and 2025, pulling together a digital atlas of these storms.
They analyzed 900 in total and found the maximum windspeed of the most intense nor’easters increased by around 6% since 1940, according to the study published Monday in the Proceedings of the National Academy of Sciences.
This may sound small but it vastly increases the damage a storm can wreak. A 6% boost in wind speed equates to a 20% increase in the storm’s destructive potential, Mann said. “That’s substantial.”
The rates of rain and snow dumped by these storms have also increased by about 10%, according to the analysis.
The reason nor’easters are intensifying is “basic physics,” Mann said. Warmer oceans and air mean more evaporation and more moisture in the atmosphere, which gets wrung out in the form of more intense rain or snow.
The level of damage these storms can inflict make it vital to better understand how they’ll change in a hotter world, Mann added.
The “Ash Wednesday” storm in 1962, for example, caused huge devastation along the East Coast, inflicting a total economic loss equivalent to tens of billions of dollars in today’s money. It did “as much damage as a major landfalling hurricane,” he said.
The results also suggest the flooding risk in many East Coast cities may be underestimated, the study noted. “Nor’easters have been neglected, and that’s another contribution to increased coastal risk that we haven’t really been focusing on enough,” Mann added.
Jennifer Francis, a senior scientist at Woodwell Climate Research Center who was not involved in the study, said the findings highlight the need for better preparedness.
“Coastal communities in the Northeast where nor’easters strike should sit up and take notice… proactive preparation is less costly than post-storm recovery,” she told CNN.
The findings are also important because they shine a light on the different ways the climate crisis plays out, said Judah Cohen, an MIT climatologist who was also not involved in the study.
The effects “can be counter-intuitive, including the idea that climate change can result in episodic increases in severe winter weather,” he told CNN.
Even as the world warms, and the snow season shortens in many parts of the US, there will still be periods of heavy snowfall and intense cold, Mann said. “Individual events may pack a bigger punch.”
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