More than 400 US cities and towns could be “past the point of no return” and will be submerged by rising sea levels, a new study has claimed, agencies report.
Cities including New Orleans and Miami could see more than 50% of populated land underwater whether or not action is taken to cut carbon emissions.
A study published in the Proceedings of the National Academy of Science journal said that land in 414 US cities, home to more than 20 million people, is under threat from higher sea levels if action is not taken.
Lead author Ben Strauss, vice president for sea level and climate impacts at Climate Central, said scientists have forecast that sea levels will rise between 14ft and 32ft up to the year 2100 if nothing is done to reduce the burning of fossil fuels.
The study forecasts what could happen at current carbon emission levels, if the West Antarctic ice sheet melts and if if the carbon emissions peak was reached earlier than the current aim of 2050.
It found that the 414 cities and towns have “lock-in” dates, the point where more than half of the city’s land will eventually be underwater regardless of efforts to reduce carbon emissions.
Mr Strauss told The Huffington Post the lock-in date was “the date where we let the genie out of the bottle, when it’s past the point of no return”.
New Orleans and Miami have already passed those dates. Mr Strauss said: “Even in a best-case carbon scenario, 98% of populated land in New Orleans would be below the future sea level.
“So it’s really just a question of building suitable defences or eventually abandoning the city. “The extra problem that Miami has is that it’s sitting on porous limestone, or, in other words, the bedrock underneath Miami is a lot like Swiss cheese.
“Water can just go through it and so building levees is not going to be effective in South Florida.” The state of Florida has the highest number of cities at risk from rising sea levels.
California, Louisiana and New York are the next three most-affected states. The study adds: “Although past anthropogenic emissions already have caused sea-level commitment that will force coastal cities to adapt, future emissions will determine which areas we can continue to occupy or may have to abandon.”
Under a worst-case scenario, New York could be uninhabitable by 2085, according to the study.
But 14 cities – including Jacksonville, Virginia Beach and Sacramento – could avoid “lock-in” dates this century if carbon emissions were reduced to 1950s levels.
Mr Strauss told The Huffington Post: “To me this is really a question of our American legacy and American heritage.
“Are we going to let the ocean take a state-sized bite out of America? If we make extreme efforts to cut carbon, we can avoid that.”
At current carbon emission levels, cities including Charleston, Jacksonville, Miami, New Orleans, Sacramento and Virginia Beach could see 50% of land below future sea levels, the study found.
Boston, Honolulu, Long Beach, New York and Tampa could see 25% of land below the water.
An online tool by Climate Central allows users to see how rising sea levels will affect US cities. A global version is being planned by the organisation.