Global sea levels could rise as high as 3 meters if the Thwaites Glacier collapses in West Antarctica.
Sea level rise threatens cities from Shanghai to London, to low-lying parts of Florida or Bangladesh, and to entire countries such as the Maldives.
In the UK, for example, an increase of 2 meters (6.7 ft) or more could put areas such as Hull, Peterborough, Portsmouth and parts of East London and the River Thames at risk of flooding.
The glacier collapse, which could begin decades, could also weaken large cities like New York and Sydney.
Parts of New Orleans, Houston and Miami in the southern US would also be particularly hard hit.
A 2014 study by the Union of Concerned Scientists looked at 52 sea level indicators in communities across the U.S.
Tides floods were found to increase dramatically in many locations on the east and gulf coast, based on a conservative estimate of predicted sea level rise based on current data.
The results showed that most of these communities will see a sharp increase in the number and severity of tidal floods in the coming decades.
By 2030, more than half of the 52 communities surveyed are expected to experience floods in exposed areas on average 24 times a year, assuming moderate sea-level rises. Twenty of these communities could see triples or more in tidal floods.
The mid-Atlantic coast is expected to see some of the biggest increases in flooding frequency. Places like Annapolis, Maryland, and Washington, DC can expect more than 150 floods a year, and 80 locations or more can occur in several locations in New Jersey.
In the UK, a two-meter (6.5 ft) rise by 2040 would project large parts of Kent almost completely underwater, according to the results of a paper published in Proceedings of the National Academy of Science in November 2016.
Areas on the south coast such as Portsmouth, as well as Cambridge and Peterborough are also said to be hit hard.
Cities and towns around the Humber Estuary, such as Hull, Scunthorpe and Grimsby, would also face intense flooding.