Protecting Coastal Cities From Rising Seas

Vanishing coastlines are a major test for government action. For many cities, especially those in nations that have made incremental progress on national climate change policy, and even those like Venice that have grappled with a rise in water levels for decades, the time to act is now.

Mumbai

The International Panel on Climate Change (IPCC) projected in 2007 that global sea levels would rise between 8 inches and 2 feet over the next century. But thanks to persistently high air and sea temperatures over the past six years, glaciers are melting, polar ice caps are shrinking, and ice is being lost from the continental sheets of Greenland and West Antarctica at a faster rate than anticipated. Combining these new developments with the expected thermal expansion, scientists writing for Environmental Research Lettersanticipate that global sea levels will rise between 12 inches and 3 feet over the next century—a 60 percent increase over the IPCC model.

That means the coastlines around more than two-thirds of the world’s largest megacities and the sprawl that surrounds them are disappearing much faster than predicted. With millions of urbanites’ security at risk, the consequences of not taking preventive measures go far beyond a sinking Piazza San Marco. Warmer, higher oceans dramatically increase the risk of frequent extreme weather events, damaging floods, and storm surges. Recent storms likeHurricane Sandy on America’s East Coast, with damages totaling over $50 billion for the entire region, and the 2008 Cyclone Nargis in Myanmar, with a death toll that climbed to nearly 140,000 lives, demonstrate the varied and damaging repercussions of sea-level rise all too clearly. Residences, transportation infrastructure, schools, hospitals, industry, and commercial areas, among other valuable urban assets, will face billions of dollars in climate-related damages over the coming decades.

CITIES AT ECONOMIC AND ECOLOGICAL RISK

From Ephesus, Turkey, to Mumbai, India, urban settlements along the sea have been important concentrations of cultural, economic, and population growth for millennia. Today, some of the world’s largest megacities and suburbs, with growing populations of more than 10 million, are also those most vulnerable to sea-level rise. Over the next half century, urban coastal communities around the world will face a new reality of dangerously amplified security risks, loss of life, and economic destruction from climate-change-induced flooding and storm surges.

Kolkata, India, for instance, is expected to contain more than 14 million people in locations vulnerable to rising sea levels and increased flooding by 2070, a sevenfold increase over its exposed population of 1.9 million today. Sea-level rise will jeopardize not only the homes and livelihoods of those 14 million people but also—and perhaps most importantly—their basic safety.

But Kolkata is not the exception—it’s the norm. Most of the top ten port cities with the largest number of people exposed to coastal flooding are growing and industrializing Asian cities (see table 1). Collectively, they are home to a total of nearly 66.4 million people and have combined future exposed assets of more than $19 trillion (see table 2). More

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