4 Million Americans Threatened by Rising Seas

Nearly 4 million Americans, encompassing a total area larger than the state of Maryland, could be underwater by the end of the century, suggest two new studies predicting the risk of flooding due to sea-level rise in the United States.

The news comes on the heels of reports that the Pacific nation of Kiribati is in negotiations to buy land on Fiji so Kiribati residents under threat of rising seas can move there.

As the planet warms, seas are expected to rise due to thermal expansion (water expands as it warms) and glacier melt. In their most recent report, the Intergovernmental Panel on Climate Change (IPCC), the international body charged with assessing climate change, estimates the seas will rise up to 6.6 feet (2 meters) by 2100; this number could be higher depending on the degree of ice melt at the poles and greenhouse gas emissions.

More extreme weather as a result of climate change is also expected, according to the IPCC report.

"The sea-level rise taking place right now is quickly making extreme coastal floods more common, increasing risk for millions of people where they live and work," Ben Strauss, co-author of both studies and researcher at Climate Central, said in a statement. "Sea-level rise makes every single coastal storm flood higher."

Strauss added, "With so many communities concentrated on U.S. coasts, the odds for major damage get bigger every year." [Infographic: US Coastal Population]

Both studies are detailed today (March 14) in the journal Environmental Research Letters.

In the first study, researchers from Climate Central and the University of Arizona created a model assuming a sea-level rise of 3.3 feet (1 m) or more by the end of the century. Results showed that in terms of area affected, regions surrounding the Gulf of Mexico may be the most vulnerable to flooding; in terms of population, Florida is the most vulnerable, closely followed by Louisiana, California, New York and New Jersey, they found.

The researchers also think Los Angeles is an area of concern due to its large population and previous research suggesting floods in southern California could reach rarely seen heights more quickly than in any other mainland U.S. area.

In the second study, researchers combined past data on the effects of heavy storms on water levels with estimates of future global sea-level rise. The past water level data came from 55 stations across the United States. The results suggest water levels that have previously been encountered only once a century could occur every decade or more, the researchers said.

The researchers liken the type of annual flooding that we may see to the infamous high water levels brought about in New York in 1992 by a strong nor'easter, which flooded the subway system.

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