Next fall, San Francisco International Airport plans to begin environmental studies for its next big construction project. The $587 million project, targeted for completion in 2035, won’t produce another terminal, runway, or amenity for the airport’s 55 million annual passengers. It will be a seawall, an 8-mile-long bastion of steel and concrete. It will also be the centerpiece of SFO’s plan to protect itself from the steady rise of San Francisco Bay.

Since the 1980s, SFO has installed a variety of features to protect itself from the risk of flood associated with rising waters, including berms, concrete walls, and the kind of sheet piling construction projects use to keep water out of building sites. The new wall betrays a bolder ambition, to keep the airport’s facilities and four runways dry for the next half century or more. That means building to protect against 3 feet of sea level rise, the level anticipated by 2085. And while San Francisco International has one of the better-defined plans for warding off the water, it’s far from the only American airport facing this challenge.

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Rising tides may lift boats, but they can sink airplanes. According to the 2014 National Climate Assessment, 13 of the country’s 47 largest airports have at least one runway that’s vulnerable to moderate or high storm surge. Along with San Francisco and its across-the-bay buddy Oakland International, these include the New York area trio of Kennedy, LaGuardia, and Newark. Boston’s Logan and Philadelphia International are at risk, as are Washington, DC’s Reagan and Honolulu International. The waters pose a threat to airports in Fort Lauderdale, Florida, Miami, New Orleans, and San Juan, Puerto Rico. It’s not that the waters will come up and swallow these places the way an incoming tide swallows a sandcastle—at least not this century. Rather, the higher water levels will exacerbate the effects of storms, making floods more common and damaging.

The list of threatened airports is long because coastal areas make for good places to put planes: They tend to be flat and low-lying, and their bodies of water provide lots of open space for arriving and departing aircraft. But as climate change takes hold—spurred on by the emissions that jet aircraft pump into the atmosphere—that convenience has become a vulnerability. And though airports have long been aware of that shift, the pummeling that Superstorm Sandy dealt to New York City in 2012 made clear the severity of the problem. Water overtook LaGuardia’s runways and damaged electrical infrastructure, forcing a three-day closure that cost millions.

Like most problems posed by a shifting climate, the fixes are neither easy nor cheap. The obvious option is to keep the water out. That’s the goal of SFO's seawall. Oakland's airport plans to fortify and raise by 2 feet the 4.5-mile dike that separates its main runway and terminals from the bay. That should cover it until 2050, for $46 million.

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