This April 24, 2005 aerial view shows Miami Beach. The world's 136 largest coastal cities could risk combined annual losses of $1 trillion (750 billion euros) from floods by 2050 unless they drastically raise their defences, a study warned Sunday.

The world's 136 largest coastal cities could risk combined annual losses of $1 trillion (750 billion euros) from floods by 2050 unless they drastically raise their defences, a study warned Sunday.

Current  are about $6 billion per year, with four cities— Miami, New York and New Orleans in the United States and Guangzhou in China—incurring 43 percent of the costs, according to a report in the journal Nature Climate Change.

World Bank economist Stephane Hallegatte and colleagues composed a loss risk scenario based on city  as well as different levels of sea level rise,  upgrades and subsidence—the sinking of surface areas often linked to the extraction of oil or other ground resources.

Assuming cities improve their protection to contain the  to current levels, and based purely on the projected growth of city populations and the assets accumulated there, the team warned of a nine-fold increase in losses to $52 billion per year by 2050.

When the team adds the -induced  and subsidence, the figure increases to between $60 and $63 billion per year.

"With no adaptation (of ), the projected increase in average losses by 2050 is huge, with aggregate losses increasing to more than $1 trillion per year," said the study—a worst-case-scenario outcome that would roughly equate to the 2012 GDP of Iran.

More of the story, click image