A rise in sea levels has already sealed the fate of at least 316 American cities, including Miami and Jacksonville, but if global warming keeps up its current rate through 2100, the number of towns and cities doomed by water could easily go up to 1,400, a chilling new study says.

Prior greenhouse gas emissions “have already locked in four feet of future sea-level rise that will submerge parts of 316 municipalities,” says the paper that was published in the Proceedings of the National Academy of Sciences.

“It’s like this invisible threat,” Benjamin Strauss, a scientist at Climate Central, a non-profit research group based in Princeton, N.J., and author of the paper told USA Today.

But Strauss says the timing isn’t clear and the inundation could take hundreds of years.

“It is much easier to know that a pile of ice in a warm room will melt than to know exactly how fast it will melt,” Strauss wrote in his analysis.

An interactive map on the website of Climate Central shows the cities and towns that are under threat.

Florida, by far, is the most vulnerable U.S. state under any emissions scenario while New Jersey, North Carolina and Louisiana would also face an uphill battle against climate change.

Across the U.S., the largest threatened cities are Miami, Virginia Beach, Va., Sacramento, Calif., and Jacksonville, Fla.

The paper is not the first of its kind but the grimmest.

Recent research has indicated that warming from carbon emitted today is essentially irreversible and will persist for hundreds or thousands of years, thus pushing the unstoppable sea level rise.

In his blog, Strauss explains that it’s a mistaken notion that if greenhouse gas emissions stop today, or soon, the problem of rising sea levels will evaporate. That will not happen because carbon dioxide remains in the atmosphere for centuries and contributes to the two factors that raise sea levels: increasing temperatures and loss of Greenland and Antarctic ice.

To calculate the U.S. cities at risk, Strauss took a unique approach: he analyzed elevation data and 2010 census population numbers and then blended that with a finding led by Anders Levermann of the Potsdam Institute for Climate Impact Research. Levermann found that each degree Fahrenheit of global warming translates to 4.2 feet (1.3 metres) of sea-level rise in the long run.

Levermann’s paper was also published in the PNAS journal recently.

Jason Thistlethwaite, the director of University of Waterloo’s Climate Change Adaptation Project, says Strauss’ paper is alarming on several levels.

“I was shocked by how much sea-level rise is already predicted to occur . . . and even if we do a good job fighting climate change and reducing greenhouse gas emissions, we are looking at seven to 10 feet (of) sea-level rise by the end of century.”

Thistlethwaite says the paper wasn’t an exaggeration in any way.

“There’s a pattern of evidence that we have been seeing for the past few years,” he said, adding the economic implications will be gargantuan.

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“When big cities have significant damage, there is spillover effect for the economy,” said Thistlethwaite.

Strauss’ analysis says that more than 3.6 million Americans live in the 316 municipalities that are already in trouble.