Up to 13M Americans at risk from sea-level rise — study

Source: Amanda Reilly, E&E reporter • Posted: Tuesday, March 15, 2016

As many as 13 million people in the continental United States may be at risk from flooding due to sea-level rise by the year 2100, according to a study out today.

Thirty-one counties could each see more than 100,000 people affected by 6 feet of sea-level rise, the study led by the University of Georgia found. The southeastern United States is likely to be hardest hit, representing 70 percent of the U.S. population that’s at risk, according to the data.

“These results suggest that the absence of protective measures could lead to U.S. population movements of a magnitude similar to the twentieth century Great Migration of southern African-Americans,” the authors wrote, referring to the movement of millions of African-Americans in the early 20th century away from the South.

The study, published this afternoon in the journal Nature Climate Change, used a combination of future population projections and government estimates of sea-level rise. Prior studies have estimated risk levels from sea-level rise, but the authors of today’s research say others have relied on current population data, rather than projections of future population patterns, to assess risks.

The Georgia Sea Grant College Program and the National Oceanic and Atmospheric Administration funded the study. The researchers used NOAA data sets covering 319 coastal counties in the continental United States.

Globally, sea-level rise scenarios by the year 2100 range from 0.3 meter to 2.0 meters due to climate change, according to a study cited by the authors that was published in 2009 in the journal Proceedings of the National Academy of Sciences. The higher figure is linked to a collapse of the polar ice sheets.

Today’s study found that sea-level rise of 0.9 meter by 2100 would put 4.2 million people in the continental United States at risk of inundation. A sea-level rise of 1.8 meters would affect 13.1 million Americans.

The results suggest that impacts from future sea-level rise will be “highly regionalized,” the study said.

More than 10 percent of the future coastal populations of Georgia, South Carolina and Louisiana are at risk under the high-rise scenario. Florida’s Miami-Dade and Broward counties represent more than a quarter of all the people affected by future sea-level rise.

The study warned that three low-lying counties — Tyrrell, N.C.; Monroe, Fla.; and Hyde, N.C. — were the most vulnerable with a 1.8-meter rise. Those three counties could see more than 80 percent of their people affected by flooding. Tampa-St. Petersburg, Fla.; Charleston, S.C.; Poquoson, Va.; and Cape May, N.J., may also experience “serious levels of population impact” under that scenario, according to the authors.

Those results are nearly triple the estimated risk that has been found when current population data are used, according to the authors.

“Our work indicates that existing estimates of future adaptation cost may, in fact, be deceptively low,” they wrote, “if future population growth is not taken into account.”

Authors said they hope policymakers use the results to target where interventions are needed most.

“It gives policymakers more detailed information to help them assess how sea-level rise will affect people and infrastructure,” said Mathew Hauer, a researcher at the University of Georgia and lead author of the report. “Adaptation strategies are costly, and these are areas of especially rapid population growth, so the longer we wait to implement adaptation measures, the more expensive they become.”

Correction: An earlier version of this article said the study by Proceedings of the National Academy of Sciences found that sea-level rise of 0.9 meter by 2011 would put continental United States at risk of inundation; it should be by the year 2100.