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RENEE MONTAGNE, HOST:
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It will take tens of billions of dollars to repair the damage from Hurricane Sandy. And that's just the first challenge. Scientists who study climate change say repair is not enough. As the climate warms, ice sheets and glaciers will melt, raising the sea level. That means coastal storms in the future will likely cause even more flooding.
New Yorkers and scientists face a tough decision: How to spend limited funds to deal with what experts are calling the new normal.
NPR's Christopher Joyce reports on that debate.
CHRISTOPHER JOYCE, BYLINE: New York City faces the Atlantic Ocean like a chin waiting to be hit. And Sandy stepped up and whacked it. And there will be more Sandys. Here's Jane Lubchenco, who heads the National Oceanic and Atmospheric Administration, which includes the National Weather Service.
DR. JANE LUBCHENCO: Storms today are different. Because of sea level rise, the storm surge was much more intense, was much higher than it would have been in a non-climate-changed world.
JOYCE: Even garden-variety storms may some day heave water up to your doorstep. So the question now is how to prepare for the next big one? Some things are a given - you can see this as you drive through Staten Island's shore neighborhoods. Many of these houses are a coin toss above sea level. Sandy knocked one-story bungalows off their foundations and flooded the rest.
Repair crews go from house to house, cutting up soggy flooring and hauling away debris. Green and yellow stickers on the front doors tell a story. Yellow means the house is not inhabitable. Green means it's OK.
Marit Larson, with the city's parks and recreation department, says most of the OK ones were built after the late 1990s, when building codes changed.
MARIT LARSON: Zoning codes required that no utilities were in the basement, so they...
JOYCE: Utilities meaning electrical switching boxes and that sort of thing?
LARSON: Electrical, and gas and, you know, heating, so whatever their utilities they had, had to be built on the second floor.
JOYCE: In between houses you can see wetlands - tall reeds and twisted trees in standing water. Larson says, normally, they slow runoff from rainstorms. But Sandy's 10-foot-high surge here overwhelmed them.
LARSON: Just simply the amount of water that came in and inundated these people's property, so that couldn't be held back by these wetlands.
JOYCE: Larson says wetlands could be useful for future storms, however, if you put them in the right place and make them big enough.
Along a beach for example, wetlands help blunt the energy of incoming waves. But you need more. At this beachfront community, the beach is flat and narrow and it's not much help.
Engineer Franco Montalto from Drexel University says it could be nourished, built up with sand or sediment to create dunes that hold back the water.
FRANCO MONTALTO: And the evidence seems to be that places that had rehabilitated beaches suffered less damage than places that didn't.
JOYCE: For years, the Army Corps of Engineers has built sand dunes along East Coast beaches. Although many got swept away by Sandy, they're relatively cheap to rebuild. It's the kind of defense that Montalto calls green infrastructure. He says the green strategy has multiple benefits.
MONTALTO: You know a beach nourishment project could have value in terms of protecting houses, it could add habitat and it could, sort of, enhance the value of this beach.
JOYCE: New York is seeking about $10 billion just to prepare for the next big storm. Some experts, like Montalto, say you get more bang for your buck with a distributed defense - dunes, wetlands, bigger storm water culverts, even urban parks that slow down the flow of water. They're cheaper and designed to fit the needs of a particular community.
But city officials are also contemplating plans to build huge sea walls across the mouths of the Hudson and East Rivers, for example, and even one from New Jersey to New York. Each would cost $6 billion or more.
Klaus Jacob is a skeptic about sea walls. He's a geoscientist at Columbia University's Lamont-Doherty Laboratory in New York.
KLAUS JACOB: The only thing that barriers do is prevent storm surges. Now, that's wonderful. It would have taken care of Sandy and will take care of future storm surges up to a point.
JOYCE: That point being, when sea level rises enough to push a storm surge over the top of the sea wall. Since no one knows how high levels will go, a sea wall could become obsolete in a few decades. Moreover, a sea wall is open most of the time to let traffic through. So as the ocean rises, it will raise the river level too.
JACOB: So now we have barriers. The sea level rise still goes wherever it wants to go.
JOYCE: Jacob isn't against sea walls but he says the city needs to figure out ways to live with higher sea levels and flooding, even if that means abandoning some flood zones. Cynthia Rosenzweig, a climate scientist at NASA's Goddard Institute for Space Studies, says most New Yorkers have reached a tipping point on the subject of climate change.
CYNTHIA ROSENZWEIG: The evidence is indeed piling up, that climate change is no longer something that is happening in future decades, and everyone's eyes are glazing over as the scientists are talking about it.
JOYCE: Rosenzweig co-authored a report that looked at the costs and benefits of preparing the city for climate change. It calculated that $1 of prevention saves $4 in future repairs.
ROSENZWEIG: If we're going to be having this much damage again and again, our whole economy of our region will not be able to survive.
JOYCE: And as former New York Mayor Ed Koch once said, New York City is where the future comes to rehearse. Christopher Joyce, NPR News.