Damage—and Cost—of Sea Level Rise Will Rise Faster Than Sea Itself

Flooding in Britain
Members of the emergency services rescue a woman from a flooded house in York, after the river Ouse in northern England burst its banks, on December 28, 2015. Andrew Yates/Reuters

We already knew sea level rise is likely to wreak havoc on cities across the globe within the next century and beyond. With half the world's population (and more than half the U.S. population) living on the coast, and three-quarters of the world's cities built right by the sea, any change in sea height is going to be felt by many, many people and the infrastructure that supports them. But what scientists just determined is that the damage costs will rise even faster than the seas themselves.

In a paper published in the journal Natural Hazards and Earth System Sciences on Sunday, researchers from the Potsdam Institute for Climate Impact Research and the University of Potsdam in Germany explained that cities have much more money at stake due to sea level rise than they might think.

By developing a way to translate increased flooding (caused by rising seas and more frequent and severe storms) into inundation-related damage to the cities themselves, the researchers were able to calculate how quickly damage added up with each centimeter of sea rise. The calculation they developed is also able to take into account potential preventative infrastructure, like dikes or seawalls—which could help cities determine the real value of investing in climate-related natural disaster mitigation projects.

For example, the researchers found that in Copenhagen, Denmark, a sea level rise of just 11 centimeters (or just over 4 inches) by mid-century would lead to $1.1 billion in economic losses. And that's a relatively conservative estimate; Denmark as a whole is projected to experience between 10 and 40 centimeters of sea level rise by mid-century. The researchers told Reuters if the rate of sea level rise doubles from that conservative estimate to about 25 centimeters (9.8 inches) by mid-century, the damage costs would quadruple to $4.35 billion.

"When sea levels rise, damage costs rise even faster, our analyses show," Markus Boettle, a researcher at the Potsdam Institute for Climate Impact Research and the lead author of the study, said in a statement, adding that it's not just environmental factors cities should worry about. It's also how well they choose to adapt. How much damage a city will incur is determined to a "significant extent by human decisions: flood defense measures can counteract the increasing flood risk." His team's calculation could help cities understand the economic benefits of preparing and adapting the city for future sea level rise.

"Our equations basically work in Mumbai, New York, Hamburg—Pacific, Atlantic, or North Sea. In any location worldwide the same simple and universal expressions hold true," Jürgen Kropp, a co-author on the study from the Potsdam Institute for Climate Impact Research, said in a statement.

With the seas rising faster than they have at any period at least since the founding of ancient Rome, and with them likely to continue rising for at least 300 years, even if we dramatically cut emissions now, knowing how much is at stake will be key to the future of major metropolises around the world.