Rising Seas Could Threaten 180 U.S. Cities by 2100

Rising seas spurred by climate change could threaten 180 U.S. coastal cities by 2100, a new study says, with Miami, New Orleans and Virginia Beach among those most severely affected.

Previous studies have looked at where rising waters might go by the end of this century, assuming various levels of sea level rise, but this latest research focused on municipalities in the contiguous 48 states with population of 50,000 or more.

Cities along the southern Atlantic coast and the Gulf of Mexico will likely be hardest hit if global sea levels rise, as projected, by about 3 feet [app. 1 meter] by 2100, researchers reported in the journal Climate Change Letters. Sea level rise is expected to be one result of global warming as ice on land melts and flows toward the world’s oceans.

Using data from the U.S. Geological Survey, the scientists were able to calculate in detail how much land could be lost as seas rise, said study author Jeremy Weiss of the University of Arizona.

Rising coastal waters threaten an average of 9 percent of the land in the 180 coastal cities in the study. Miami, New Orleans, Tampa, Florida, and Virginia Beach, Virginia could lose more than 10 percent of their land area by century’s end, the study found. New York City, Washington D.C. and the San Francisco Bay area could face lesser impacts.

The effects of higher seas can range from erosion to permanent inundation, and the severity of the damage depends in great measure on where the cities are, Weiss said.

“In Miami, it’s not just strictly along their coastal edge. They have to worry about the issue in all directions,” because much of the area around Miami is relatively flat, making it more vulnerable to encroaching waters,” he said.

“By contrast,” he added, “people in the New York metropolitan area can concentrate their efforts along the shorelines because the land rises quickly away from the coast.”

Sea level rise is expected as a consequence of continuing climate change, which is spurred by human activities including the burning of fossil fuels.

The U.N. Intergovernmental Panel on Climate Change (IPCC) has estimated global average temperature will rise by 3.6 degrees F [1.8°C] by 2100. However, Weiss and his colleagues put the warming at more like 8 degrees F [4.44°C].

Weiss said the lesser degree of warming projected by the IPCC reflects a moderate scenario. The study’s higher temperature estimate is based on the idea that greenhouse emissions will continue along the current trajectory.

After 2100, Weiss said, sea levels could rise as much as 6 yards, based on the melting of giant ice sheets covering Greenland and Antarctica.