"For almost as long as people have been building near beaches, they have been protecting those buildings with sea walls. These barriers, which deflect strong waves and prevent coastal erosion, were constructed around ancient Roman harbors and medieval British cities. Archaeologists in Israel have even uncovered evidence of a 7,000-year-old rock wall constructed in the aftermath of the Ice Age to hold back rising oceans as the world defrosted.
But modern, human-caused climate change is escalating the threats that make sea walls necessary. Sea levels are rising, putting communities at greater risk from floods. Storms are intensifying, causing more and more sand to erode from beaches. Cities such as New York, Boston and Miami — as well as smaller, beachfront communities from California to Cape Cod — could lose thousands of homes and suffer billions of dollars in damage if they don’t find a way to hold back the water.
Sea walls have been credited with saving lives in extreme events. When the 2004 Christmas Day tsunami bore down on the Indian coastal city Pondicherry, a 300-year-old sea wall prevented powerful waves from flooding the city center."