By 2070 the climate change may more than triple the number of people threatened by coastal flooding while the financial impact could surge by tens of trillions of dollars.
Angel Gurria, secretary general of the Paris-based Organization for Economic Cooperation and Development, called for quick action to buy time for cities at risk. It can take 30 years to put defenses for vulnerable cities in place, a report published by the organization Tuesday said.
"Climate change is already happening and concerted action is needed now to prevent its worst impacts," the organization quoted Gurria as saying. Gurria is scheduled to take part in the U.N. Climate Change conference in Bali, Indonesia.
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 half-meter (1.6 feet).
The study estimated the financial impact of such a scenario at US$35 trillion, compared to US$3 trillion today.
The development of Asian "mega-cities," with their soaring populations, was pointed to 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.