New York City is at least twenty times more likely to see flooding during extreme weather events than it was in the 18th century, according to a new study, of changing environmental conditions. That means that fallout from storms like Hurricane Sandy, which cost the U.S. $65 billion in damages, could happen more often.

CBS explains that the researchers, Stefan Talke, Philip Orton and David Jay examined tide gauges dating back to 1844 to determine the trend of rising sea swells. Talke described the process as similar to looking at a time-lapse photo of the city in the following video: 

The authors of the study write in the paper's abstract that "Three of the nine highest recorded water levels in the New York Harbor region have occurred since 2010, and eight of the largest twenty have occurred since 1990."

They conclude that "the annual probability of overtopping the typical Manhattan seawall [has risen] from less than 1% to about 20-25%." This is because the maximum storm-time water levels by the NY Harbor have risen by two-and-a-half feet since the mid-19th century --  about a foot more than the global sea-rise level. According to Talke, the concerning data could help the city prepare for future disasters.

National Geographic explains that the change means there will be an increase in "ten-year" storms, or major storms that have a ten percent chance of occurring in any year: 

After analyzing the data, Talke and team concluded that New York City is at risk of more frequent and extensive flooding than had been expected due to sea-level rise alone. A major, "ten-year" storm today would cause bigger storm tides and more damage than a ten-year storm in the mid-1800s.

Talke said he thinks the increased rise stems from a combination of changes in the harbor and global warming, which is causing sea levels to rise. 

And director of Resiliency for the City of New York Daniel Zarrilli, who is tasked with ensuring that the city is prepared for hurricanes and other storms, seems confident that global warming is making things worse. "Historic sea-level rise has clearly increased the odds of flooding in New York Harbor. Climate change will only accelerate that impact."