Coastal flooding could cost the global economy $1-trillion a year a few short decades from now because of the rise in sea levels caused by global warming if action is not taken now to stem the flow and Vancouver is one of the cities most at-risk for losses, says a new study.

The article, published Tuesday in the journal Nature Climate Change, is part of an ongoing project by the Organization for Economic Co-operation.

"This work shows that flood risk is rising in coastal cities globally due to a range of factors, including sea-level rise," Robert Nicholls, a professor of coastal engineering at the University of Southampton in the United Kingdom and co-author of the study, said in a news release.

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"Hence, there is a pressing need to start planning how to manage flood risk now."

The authors based their prediction on an increase in sea levels of between 0.2 and 0.4 metres by 2050 caused by melting continental ice sheets.

The University of Southampton team looked at population, flood protection infrastructure and elevation of storms.

They looked at 136 of the largest coastal cities in the world, and found that losses from flooding could hit $63-billion (U.S.) a year by 2050.

Without efforts to adapt, total annual losses could top $1-trillion, the article said. By comparison, average global flood losses in 2005 were estimated to be approximately $6-billion.

Inaction is not an option, the team said.

Flood defences in coastal cities have been designed for past conditions, and officials need to improve flood management and infrastructure, the study urged.

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Those improvements will cost about $50-billion a year for the 136 cities the study considered.

The list of 20 cities most at risk, based on average annual losses due to floods, is topped by Guangzhou, Miami, New York, New Orleans, Mumbai, Nagoya, Tampa-St. Petersburg, Boston, Shenzen, Osaka-Kobe and Vancouver.

However, the authors note that when defence measures are taken into account, Vancouver does not make the list, which shifts dramatically toward cities in developing countries with fewer resources to guard against flooding.

Last year, Vancouver became the first Canadian city to adopt a climate change adaptation strategy, which includes a coastal flood risk assessment and flood-proofing policies.

"I think it's another strong message about why that work is so urgent, but I don't think there's any stronger message than the floods that we saw in Calgary this past year, and in Toronto," said Coun. Andrea Reimer.

"You might be able to argue with a report. It's very hard to argue with the weather, and the observed impacts of extreme weather."

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Climate change will bring heavier precipitation, higher daily temperatures, and more extreme weather events, she said.

The sea level in the city rose by almost 20 centimetres over the past century, and that rate is increasing rapidly, said Vancouver's report.

One local study suggested $25 billion worth of real estate alone will be at risk from rising waters by the end of this century.

"Climate change is imposing threats along coasts, both from rising sea levels and increased intensity and frequency of storms," it said.

Vancouver's plan calls for the city to improve infrastructure to deal with flooding and extreme heat and storms.

Stephane Hallegatte, a senior economist with the World Bank and lead author of Nature paper, said policy makers should be considering early warning systems and evacuation planning.

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"There is a limit to what can be achieved with hard protection: populations and assets will remain vulnerable to defence failure or to exceptional events that exceed the protection design," he said.