Map: Oysters, Reefs, and Swamps Protect Billions' Worth of Real Estate—For Free

Among the hundreds of recommendations listed in Mayor Michael Bloomberg's $20 billion plan to protect New York from climate change is a call to stock up on oysters. Not the kind you'd want to knock back with a nice pilsner on a Friday afternoon: The idea is to build large underwater oyster reefs around the harbor that could prevent coastal erosion and absorb storm surges. "Soft" infrastructure like this—reefs, wetlands, dunes, and other "natural" systems—is gaining in popularity over "hard" levees and sea walls as an effective way to insulate cities from sea level rise.

Turns out, some of the best of these defenses might already be in place: Yesterday the journal Nature published the first-ever nationwide maps that reveal just how much existing coastal habitats are going to save our butts from rising seas and wild storms. Remove reefs, coastal forests, marshes, kelp beds, and other coastal habitats, the study finds, and twice as much coastline and 1.4 million more people will be highly exposed to climate risks.