New research indicates sea-level rise, largely driven by climate change, threatens the lives of millions living along coastal areas in the U.S. This, researchers say, is three times greater than previously estimated. 

Scientists from the University of Georgia (UGA) have for the first time examined the risks associated with rising seas using year 2100 population forecasts for all 319 coastal counties in the continental U.S. Until now, researchers relied on current population figures to assess long-term effects of coastal flooding. 

The researchers' projections show that a 6-foot sea-level rise will subject more than 13 million people to flooding and other hazards from rising seas.

"The impact projections are up to three times larger than current estimates, which significantly underestimate the effect of sea level rise in the United States," said Mathew Hauer, who completed the study as part of his doctoral work with the UGA Franklin College of Arts and Sciences. "In fact, there are 31 counties where more than 100,000 residents could be affected by six feet of sea-level rise."

Their study also revealed that Florida faces the most risk, with as many as 6 million residents impacted. Another 1 million residents in coastal areas of California and Louisiana could be affected, too. Even if sea levels were to rise by only 3 feet, population forecasts show that more than 4.2 million coastal residents in the U.S. would still be at risk. 

If accurate, it is believed that such a rise in sea level would trigger a relocation equal to that of the 20th-century Great Migration, where southern African-Americans moved to the North. Therefore, researchers suggest their findings can be used to develop preventative strategies. 

"This research merges population forecasts with sea level rise. It gives policymakers more detailed information to help them assess how sea level rise will affect people and infrastructure," said Deepak Mishra, one of the study researchers from the UGA department of geography.

Furthermore, if adaptive measures aren't taken, more than 25 percent of people living in major urban centers like Miami and New Orleans could face coastal flooding by the end of the century.  

"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," Hauer added.

Other areas where significant numbers of people would be at risk include Long Island in New York; Charleston, S.C; and San Mateo, Calif.

Their study was recently published in the journal Nature Climate Change.