State of the Planet

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Rising Seas Pose a Growing Threat to Coastlines

Sea-level rise combined with Typhoon Haiyan’s extraordinary power led to the deaths of more than 5,000 people in the Philippines last month. Photo: Eoghan Rice, Trócaire/Caritas

The jury is still out on how tropical storms will change as climate warms, but rising sea levels will almost certainly place more coastal property at risk of flooding, says a team of scientists writing in the journal Nature.

In a review of nearly 100 research studies, the scientists say rapidly rising seas are certain to cause more flooding and property damage triggered by tropical cyclones, or hurricanes, as they are commonly called in the Atlantic and Northern Pacific. But predicting where these storms will make landfall, or if they will become more frequent or powerful in a warmer climate, is less clear.

Global sea levels are expected to rise by about one meter by 2100, but for many coastal cities, the waters are projected to creep several times higher. Osaka, Tokyo and Manila, among others, are sinking due to natural factors, amplifying the effects of sea-level rise. China’s largest city of Shanghai, home to 23 million people, is projected to see 4.3 meters of relative sea level rise by 2100, placing half of the city at risk for flooding in an extreme storm, according to a study cited in the review. The broad, low-lying coasts of Vietnam’s Red River Delta and the United States’ Mississippi Delta are similarly vulnerable. In New York City, one meter of sea level rise is expected to increase the frequency of a 100-year flood event to once every 3 to 20 years.

“We’re not putting enough emphasis on sea-level rise and how it will make us all more vulnerable to tropical storms regardless of how they are affected by climate change,” said Suzana Camargo, a cyclone expert at Columbia University’s Lamont-Doherty Earth Observatory.

As sea levels rise, they are altering the coastlines, making them ever more susceptible to rising seas by eroding shorelines, degrading barrier islands and creating new tidal inlets. “The era of relatively moderate sea level rise that most coastlines have experienced during the past few millennia is over, and shorelines are now beginning to adjust to a new boundary condition that in most cases serves to accelerate rates of shoreline retreat,” said the review paper’s lead author, Jonathan Woodruff, a sedimentologist at the University of Massachusetts Amherst.

The review authors suggest that planners consider raising structures and building further inland, along with engineering solutions such as sediment management. “It is widely accepted that sea level will rise. We just don’t know how much,” said coauthor Jennifer Irish, an engineer at Virginia Tech College of Engineering. “We need to consider the full range of sea-level estimates and plan our engineering strategies from that, designing for moderate protection now in a way that these designs can be modified in the future if necessary. The Dutch have been dealing with this problem for centuries, so it can be done.”

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