Climate: A Valuable New Tool Lets You See Where the Sea Will Rise

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A street in Coney Island floods after Hurricane Irene in 2011.

When Hurricane Irene neared New York at the end of August, the city took the unprecedented step of shutting down the entire transit system—buses, subways and commuter trains in the largest city in America. The danger was that heavy rains from Irene could cause flooding that would swamp tunnels and tracks, causing lasting damage to the most important public transit system in the country. Fortunately, that didn’t happen—Irene weakened as it reached the city, and the catastrophe officials feared never materialized. But it was close. The Metropolitan Transit Authority lost the Port Jervis line for months at the cost of nearly $40 million. And had the storm surge from Irene been just a foot higher, it would have flooded the subways, causing billions of dollars in damages and making transportation around New York impossible.

Irene could just be a preview of what the entire country will be facing in a warmer world. According to new research by the nonprofit group Climate Central—which employs TIME contributor Michael Lemonick—about 3.7 million people live within a few feet of high tide and are in danger of being hit by more frequent coastal flooding in the future because of sea level rise caused by climate change. And if sea level rise accelerates because of rapid warming—as seems likely to happen barring major reductions in greenhouse gas emissions—major coastal floods that are now rare could become a much more frequent occurrence. “The sea level rise from global warming has already doubled the risk of extreme coastal floods,” says Benjamin Strauss, one of the co-authors of the two papers that outline the new research. “We hope this research can help everyone prepare for this.”

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Climate Central’s research—which can be accessed online at Surging Seas—doesn’t just predict sea level rise over the next century, but actually presents the data in an interactive map that allows anyone to input their ZIP code and find out how great their risk of flooding will be. Unsurprisingly, Floridians are in the greatest danger—about half the country’s at-risk population lives along that state’s low-lying coast. But cities like New York and San Francisco are also vulnerable, and if the seas rise high enough, nearly the entire U.S. coastline will be at some risk.

From Climate Central:

Rising seas dramatically increase the odds of damaging floods from storm surges. For over two-thirds of the locations analyzed (and for 85% of sites outside the Gulf of Mexico), past and future global warming more than doubles the estimated odds of “century” or worse floods occurring within the next 18 years — meaning floods so high they would historically be expected just once per century. For over half the locations analyzed, warming at least triples the odds of century-plus floods over the same period. And for two-thirds the locations, sea level rise from warming has already more than doubled the odds of such a flood even this year.

These increases are likely to cause an enormous amount of damage. At three quarters of the 55 sites analyzed in this report, century levels are higher than 4 feet above the high tide line. Yet across the country, nearly 5 million people live in 2.6 million homes at less than 4 feet above high tide. In 285 cities and towns, more than half the population lives on land below this line, potential victims of increasingly likely climate-induced coastal flooding. 3.7 million live less than 1 meter above the tide.

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The ocean has been rising slowly since the beginning of the 20th century, with the average global rise at about 8 inches. Obviously that seems like nothing—on any given day, coastal tides fluctuate far more. But that global figure masks larger change at the local level, especially in regions—like southern Louisiana—where the land is sinking or wearing away. And thanks to warming, sea level rise is accelerating to about 1 foot a century.

Again, doesn’t sound like that much. But the real risk of sea level rise isn’t that whole islands and continents will be washed away, a la Waterworld. (Well, unless you live in Kiribati in the south Pacific, where the island nation is preparing to move the ENTIRE POPULATION because of sea level rise.) It’s that coastal surges during the occasional—or perhaps not so ocassional—strong storm will become more severe as sea levels rise, threatening billions of dollars of coastal infrastructure and property that used to be well out of harm’s way. The real danger of climate change is the change—the possibility that the world as we know it will change faster than we can react to—at least without spending hundreds of billions of dollars we don’t really have.

Nor does it help that we keep putting more people and property in coastal danger zones, from Miami beach to the new condos along the East River in New York. That’s a disaster multiplier—even without storms becoming stronger, a more populated coast means more people and more money in harm’s way every time a hurricane blows in. In just three counties in southeast Florida about $30 billion in taxable property is vulnerable to global warming-related flooding. And government policy only supports that development, since taxpayers pick up the bill to rebuild damaged coastal infrastructure and property after a flood. “It’s likely that low-lying areas are going to be negatively affected,” says Strauss. “Government can try to reduce development in those areas.”

Some cities are already beginning take a few steps to prepare, including New York, where sewage stations have been raised to higher elevations to avoid storm surges. (I wrote about New York’s plans to adapt to climate change in this 2009 piece.) But we’re nowhere near ready for the kinds of adjustments that will need to be made in warmer world—nor are we acting to cut carbon emissions and slow that warming. Tools like the Climate Central research should bring the message home—the water is rising.

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