If we do not dramatically reduce greenhouse gas emissions and strengthen coastal protection, high tides and increased storms will devastate economies and communities around the world.

By the end of the century, increasing coastal flooding caused by rising ocean levels will endanger more than 250 million people and cause nearly 11 trillion euros in damage to buildings and coastal infrastructure, according to a new study led by researchers at the University of Melbourne, Australia. And all that is under a relatively optimistic climate change scenario.

The findings: The research is based on the simulation of tides, storms, wave motion and regional sea level rise under several UN IPCC greenhouse gas emission scenarios. 11 trillion figure appears on the assumption that no measures are taken to reinforce the coasts with retaining walls or other protection, and that carbon dioxide pollution peaks around 2040 and begins to fall thereafter, which would be a moderate emissions scenario.

Worst case scenario: in a scenario where emissions continue to increase unchecked over the century, coastal flooding would threaten nearly 290 million people and cost about 12 trillion euros in coastal assets, or 20% of global GDP. (However, some climate researchers argue that this “CPR8.5” scenario is becoming less likely, given the steps some countries have already taken to flatten emissions.)

) Before that: in just 30 years, nearly 204 million people and more than 9 billion euros in assets could be exposed to coastal flooding, 16% and 14% more than today, respectively, in a moderate scenario.

Northern Australia, northwest Europe, southeast China, the east coast of the US, Bangladesh and several states in India will be at especially high risk of frequent and extensive flooding, according to the study.