Flooding of major coastal cities could be costing a trillion US dollars (£639 billion) a year by 2050, say scientists.
The loss estimate is based on projections of climate change, land subsidence and urban growth in coastal centres.
Three cities in the US - Miami, New York and New Orleans - and Guangzhou in China are together expected to shoulder 43% of the burden.
The researchers based their predictions on data from 136 of the largest coastal urban settlements around the world.
They found that socio-economic changes alone were likely to raise the cost of flood damage from around six billion dollars (£4 billion) in 2005 to 52 billion dollars (£33 billion) in 2050.
Adding the effects of climate change and subsidence brought total losses to an "unacceptable" one trillion dollars. Climate change increases flooding risk both by raising sea level and triggering more frequent and powerful storms. Subsidence can result from the removal of groundwater and compression of soil beneath cities, causing land to sink below sea level.
Other cities facing the highest flood losses in 2050 included Mumbai, Jakarta, Boston, Bangkok and Abidjan. In Europe, the cities of Marseille, Naples and Athens were also at risk.
The scientists, led by economist Stephane Hallegatte from the World Bank in Washington D.C., calculated the cost of providing adequate flood protection and response strategies to be around 350 million dollars (£224 million) per year for each city. For all 136 cities studied, the combined flood defence cost was around 50 billion dollars (£32 billion) per year.
Even with these measures, annual coastal flood losses were likely to rise to between 60 and 63 billion dollars (£38 - £40 billion) by 2050.
"These estimated aggregate adaptation costs are far below our estimate of aggregate damage losses per year in the absence of adaptation, and of the same order of magnitude as residual losses with adaptation," the researchers wrote in the journal Nature Climate Change.