As sea levels rise, there are basically two options, retreat or build fortifications.

For example, a 2007 Clemson School of Architecture study suggested a 9-foot sea wall could protect the Charleston peninsula if sea levels rise by 3 feet.

On the other hand, building sea walls can mean destroying valuable marshes, which could become submerged and unable to migrate inland.

“Whether we move back from the water or build barricades in the face of a rising sea, it could cost billions of dollars to adapt to such change,” said the U.S. Environmental Protection Agency.

Coastal retreat amounts to taking people out of harm’s way, but considering the coastal population and property values, the implications are sweeping.

Rising sea levels raise questions similar to those prompted by beach erosion.

Should the government and property owners try to keep the sea at bay, as at Wild Dunes on Isle of Palms, where the ocean laps at luxury condos despite a $10 million beach renourishment effort in 2008?

Or should property be ceded to the sea, as at Hunting Island State Park near Beaufort, where popular rental cabins were abandoned and parts of Cabin Road are now underwater.

Armoring the coast can mean building walls and levies to protect low areas, as in New Orleans. But it also can involve intermediate steps by property owners, such as trip walls that don’t keep water out, but protect against storm surges.

At the marshfront Simmons Point and Tides condominiums in Mount Pleasant, and at Charleston Oceanfront Villas on Folly Beach, trip walls have dramatically lowered flood insurance costs.