More than 1,700 American cities and towns – including Boston, New York, and Miami – will have significant populations living below the high-water mark by the end of this century, a new climate change study has found.

Those 1,700 towns are locked into a watery future by greenhouse gas emissions already built up in the atmosphere, the analysis published in the Proceedings of the National Academy of Sciences on Monday found. For nearly 80 of those cities, the watery future would come much sooner, within the next decade.

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“Even if we could just stop global emissions tomorrow on a dime, Fort Lauderdale, Miami Gardens, Hoboken, New Jersey will be under sea level,” said Benjamin Strauss, a researcher at Climate Central, and author of the paper. But dramatic cuts in emissions – much greater than Barack Obama and other world leaders have so far agreed – could save nearly 1,000 of those towns, by averting the sea-level rise, the study fund.

“Hundreds of American cities are already locked into watery futures and we are growing that group very rapidly,” Strauss said. “We are locking in hundreds more as we continue to emit carbon into the atmosphere.”

Those 1,700 cities would have 25% of their populations living below the high-water mark by 2100. Some 79 cities and towns with a combined population of 835,000 would be staring down those waters by 2023. About half of the population of Fort Lauderdale, Hoboken, and Palm Beach, would be living below the high tide line by 2023.

The list of cities at risk by 2100 spanned Sacramento, California – which lies far from the sea but would be vulnerable to flooding in the San Joaquin delta – and Norfolk, Virginia. The latter town is home of America’s largest navy base, whose miles of waterfront installations would be at risk by the 2040s. The Pentagon has already begun actively planning for a future under climate change, including relocating bases.

About half the population of Cambridge, MA, across the Charles River from Boston and home to Harvard and MIT, would fall below sea-level by the early 2060s, the study found. Several coastal cities in Texas were also vulnerable.

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But the region at highest risk was Florida, which has dozens of towns which will fall below the high water mark by century’s end. Miami would be significantly under water by 2041, the study found. Half of Palm Beach with its millionaires’ estates along the sea front would be below the high water line by the 2060s. Other cities such as Fort Lauderdale were already well below sea-level.

“Pretty much everywhere it seems you are going to be under water unless you build a massive system of dykes and levees,” Strauss said. The study drew on current research on sea-level rise, now growing at 1ft per decade.

A recent study, also published in PNAS by the climate scientist Anders Levermann found each 1C rise in atmospheric warming would lead eventually to 2.3m of sea-level rise.

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