Study: Rising Sea Level Threatens Homes of 4 Million Americans

Sea-level rise associated with climate change could put more than 2 million homes at risk.

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The homes of nearly 4 million Americans could be at risk of severe flooding due to sea-level rise associated with climate change over the next 100 years, according to new research.

Climate experts say the sea level could rise up to 1 meter over the next hundred years, putting about 2.1 million homes at an elevation within 1 meter of sea level in danger of flooding. (A meter is a little over 3 feet.) Previous studies have suggested that with sea-level rise, the severity and frequency of hurricanes could increase.

[Slideshow--the 10 States at Most Risk of Flooding]

Ben Strauss, one of the authors of the report and director of the Program on Sea Level Rise at Climate Central, says that even with normal storms, millions of people are at risk.

"Our report assumes that the storms stay the same. The only change is a higher sea level," he says. A 1-foot sea-level increase is "a little like steroids for coastal floods," and people might have to adjust.

"We settled the coast assuming it was a fixed boundary, and it's not anymore," Strauss says. "Some places have no choice but to build walls, like Manhattan. These are high-density places where there's nowhere to retreat. In other places, the strategy could be to make room for the migration of beaches" by moving away from the coastline, he says.

"A lot of sea-level rise is inevitable. If we reduce our greenhouse emissions rapidly, we can make a big difference. But no matter how much we cut, we've already kind of locked ourselves into a future with a lot higher seas," he says.

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Climate scientists point to places that are already below the high tide line, such as New Orleans, to illustrate the danger of sea-level rise, but Strauss's report says people on all coastlines are vulnerable.

"With respect to potential population vulnerability, Florida stands out most, followed by Louisiana, California, New York, and New Jersey, illustrating significant exposure on every coast," the report says.

Strauss says South Florida's bedrock is porous "like Swiss cheese," making it impossible to build a sea wall. "South Florida is going to have to retreat to higher ground over time," he says. Most surprisingly, southern California is also at great risk because it rarely sees storms that go 3 feet above sea level. Add a foot of sea-level rise, and "they'll be seeing water to 4 feet regularly," he says.

"I'd imagine there's a lot of development and assets between 3 and 4 feet above sea level," he adds. "They'll be seeing coastal flooding like they've never seen before."