The result is that the risk of a storm similar to Hurricane Sandy, albeit with a slightly smaller storm surge, has gone from a one-in-500-years event in 1800 to a one-in-25-years event today. By the period between 2030 and 2045, such storms could become a one-in-five-years event, according to the projections.

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“Ultimately, the balance of evidence for our study is probably bad news for New York,” Andra Garner, the Rutgers University researcher who led the study, wrote in a comment to The Washington Post. “Although we do find minimal changes to future storm surge because of a compensation between shifting storm tracks and increasing storm intensity, we find drastic increases to overall flood heights due to rising sea-levels, which we calculate by combining storm surge with potential future sea-levels.”

The research predicts sea levels will rise steadily all the way out to the year 2300. The size of that rise, however, depends in part on the stability of Antarctica, which features large volumes of ice grounded below sea level in regions susceptible to warm ocean water. If those sections someday collapse into the ocean, all the ice sitting above sea level will drive a potentially large sea level rise.

Garner conducted the study with colleagues from Rutgers, Pennsylvania State University, the Massachusetts Institute of Technology, Princeton University, the University of Massachusetts at Amherst, the Woods Hole Oceanographic Institution, and Nanyang Technological University. The research was published in the journal Proceedings of the National Academy of Sciences.

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The group of experts includes not only hurricane specialists but also two glaciologists, the University of Massachusetts, Amherst’s Rob DeConto and Penn State’s David Pollard, who have recently produced a new simulation of the potential melting of the Antarctic ice sheet, one suggesting the potential for an over 3 foot contribution to global sea level in this century, and far more in future centuries. (This is well beyond prior expectations from global bodies like the United Nations’ Intergovernmental Panel on Climate Change.)

The study found that not only had the risk of a major surge in New York already increased, but also that, by the end of the century, it’s worse.

Specifically, the work found that the one-in-500-years flood height at the Battery, a park in southern Manhattan fronting the harbor, could range from 13.1 to 16.7 feet by the year 2100, and 16.4 to 50.5 feet by the year 2300. Much of the range in these estimates, and particularly the enormous range in the latter estimate, has to do with what happens to Antarctica. (The sea-level-rise scenarios also depend on how much humans emit to the atmosphere in the coming years.)

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What this effectively means, the study notes, is that a flood height of 7.4 feet — not far from Sandy’s 9.2 feet — will be “permanently exceeded by 2280—2300 for scenarios that include Antarctica’s potential partial collapse.”

In effect, the study shows that New York is not quite halfway through a 500-year saga of rising seas (going all the way back to 1800), and that it could get considerably worse toward the endpoint.

The study’s approach of generating “synthetic” or computerized hurricanes in enormous numbers and seeing where they land in the future has been employed in the past to determine the chances of extremely rare but devastating storm strikes in vulnerable places like Tampa Bay, Dubai, and Cairns, Australia.

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Benjamin Strauss, a sea-level-rise expert with Climate Central who was not involved in the study, praised the work in a comment requested by The Post.

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“The three most important results to me are that sea level rise has already caused a big jump in flood risk; another real jump is on the way no matter what; and the size of that jump depends a lot on how much more climate pollution we put in the air,” he wrote. “That could especially be true in the worst-case scenario of an unstable Antarctica.”

Strauss added, “it looks like under all of the main scenarios and models examined, by the end of the century if not earlier, New York would regularly see floods high enough to flood the subway system as engineered today.”

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In this future, then, it could be that storms striking New York are quite rare but pose a major risk when they do occur.

“It could be seen as good news that more storms might steer away from New York,” added Richard Alley, a Penn State glaciologist who was a co-author of the study. “It might be seen as bad news in the other places where the storms go instead. My impression is that the rare, huge storm is the most worrisome, and that having bigger storms that usually steer away from the city would leave the possibility of an occasional Sandy-type left turn bringing especially large damages to a city that had started to forget the last big hit.”

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