Experts warn that if the polar ice caps continue to melt faster under the pressure of global warming, sea waves may lap over London, New York and Hong Kong by 2100.
The world's ice sheets could retreat farther by the year 2100 than they have in the past 130,000 years, leading to a huge rise in sea level, experts say adding, low-lying islands such as Tuvalu and the Maldives look set to disappear.
Coastal cities will be forced to beef up their defences or else think about relocating.
The financial districts of London, New York and Hong Kong to name but three, lie barely above sea level, a report in the Nature magazine claims.
"I think sea-level rise is a huge threat," says Colin Prentice, who studies ecosystem responses to climate change at the University of Bristol, UK.