"In less than 40 years from now the cost to the world's biggest coastal cities from flooding is expected to have risen to $1tn – 0.7% of the value of the entire world economy in 2012."

"By 2050, flood damage in the world's coastal cities is expected to reach $1 trillion a year as sea levels rise and global warming triggers new extremes of heat, windstorm and rain.

More than 40% of these prodigious costs could fall upon just four cities – New Orleans, Miami and New York in the US and Guangzhou in China.

Stephane Hallegatte of the World Bank in Washington and colleagues looked at the risks of future flood losses in the 136 largest of the world's coastal cities.

Any coastal city is always at some risk – by definition it is at sea level, and often on an estuary or floodplain, and very often began as a seaport."

Tim Radford reports for Climate News Network August 19, 2013. [2]