The Paris-based OECD, an international non-governmental organization that collects and studies economic statistics and social data, called for quick action on coastal defenses for cities at risk, saying it can take 30 years to build defenses for vulnerable cities.
About 150 million people could be exposed to coastal flooding by 2070, up from 40 million now, according to the report. The statistics were based on a "1-in-100-year" flooding event, described as a commonly accepted risk assessment standard, with a mean rise in sea level of a 1.6 feet.
The study estimated the financial impact of such a scenario at $35 trillion, compared to $3 trillion today.
The report pointed to the development of Asian "mega-cities," with their soaring populations, as a key factor increasing the risk in coastal flooding.
Calcutta heads a list of the 10 top cities at risk in 2070 in terms of population exposure, with Mumbai, or Bombay, second. Miami, Florida, in ninth place, was the only city in a developed country on the report's list of the 10 top cities at risk due to population exposure.
However, Miami leads the list of cities with the highest value of property and infrastructure assets at risk in 2070 should that "1-in-100-year" flood occur, the report said. Miami also leads in that category today.