A new study foresees rising ocean levels eventually covering the land housing half the population in coastal cities including Miami and Fort Lauderdale.

As sea levels rise due to global warming, many coastal cities are at risk of going underwater in the coming centuries without a drastic change in carbon emissions. For some cities like Miami and New Orleans, it appears to be too late.

A study published earlier this month in the Proceedings of the National Academy of Science focuses on U.S. cities that are in danger of disappearing if humans continue producing greenhouse gases at the current rate. If massive changes haven’t been made by 2100, sea levels are projected to rise 14 to 32 feet (4.3 – 9.9 meters). This could happen as early as the next century, but it could also take several centuries – the exact timing is difficult to pinpoint.

“Just think of a pile of ice in a warm room,” explained Ben Strauss, who studies sea level and climate impacts at Climate Central, Princeton, New Jersey, and is lead author of the study. “You know it is going to melt, but it is harder to say how quickly.”

To put it simply, that’s exactly what’s happening. As the average global temperature rises due to carbon emissions, the ice at the North and South Poles melts more each year. This excess water runs off into the ocean, causing global sea levels to rise.

Higher sea levels will affect coastal cities, as the study highlights. Strauss and his colleagues pinpointed areas at risk with a population greater than 20 million. They determined what they call “lock-in dates” for many American cities, a year where the cumulative effects of carbon emissions will commit them to an eventual sea level rise that will submerge the land under half the city’s population. For example, New York City’s locked-in date is 2095, assuming current carbon emissions – and that’s one of the later dates. Many other cities like Boston, Virginia Beach, Virginia, and Chesapeake, Virginia, have locked-in dates as early as 2045.

For many cities, however, the locked-in date has already passed. That means that even with a drastic reduction in carbon emissions, the sea level will eventually rise enough to cover the land housing half of the city’s population. Florida has the most cities that have passed their locked-in date, including Miami and Fort Lauderdale.

New Orleans is faring even worse, and the state of Louisiana has already felt the detrimental effects of the rising sea levels. The already soggy state lost 1,900 square miles of land to the Gulf of Mexico between 1932 and 2000. So far, none of the major population centers have been affected, but as the PNAS study tells us, that’s going to change in the coming centuries.

This study is vital because it gives a tangible timeline of the detrimental impacts of rising sea level based on current policies of fossil fuel burning.