WASHINGTON — A little bit of sea level rise could go a long way to increasing flood risk for the globe’s coastal cities. New research finds it’s possible to reduce that risk, but not make it disappear completely. It also finds that cities not typically thought of as hot spots for sea level rise and flooding will actually be some of the biggest losers in a soggier future.
Global sea levels have risen 8 inches over the past century. Some areas have experienced even greater amounts due to land subsiding due to natural and human causes. At the same time, populations along coasts have experienced major growth. In the U.S., an estimated 87 million people live along the coast, up from 47 million in 1960. Globally, six of the world’s 10 largest cities are on the coast.
The confluence of these factors has caused major economic losses from flooding. Hurricane Sandy caused up to $70 billion in damages while Katrina caused $125 billion in losses, much of it due to rising water.
With these environmental and social trends set to continue and possibly accelerate over the next 40 years, losses due to flooding represents a key challenge for coastal cities to deal with. A Nature Climate Change study published Sunday found that costs could rise dramatically if nothing is done to account for rising seas and subsiding land.
Assuming sea levels rise 15.75 inches above today’s heights by 2050 and subsidence from human development continues, the study found that losses from flooding in 136 of the world’s coastal port cities could near $1 trillion annually by 2050.
The estimate of 15.75 inches is within the range of probable sea level rise scenarios according to a 2012 National Oceanic and Atmospheric Administration report.
However, if $1 trillion in annual losses sounds implausible, that’s because it basically is. “To get to $1 trillion, we have to basically have places which are destroyed every two years and are rebuilt again and again,” Stéphane Hallegatte, a senior economist at the World Bank and lead author of the study, said. “It’s not a realistic scenario; it just shows it’s impossible to have a scenario that we do nothing.”