Some cities in the southern part of the U.S. state of Florida, including Miami Beach, are already working to stem the rising tides by installing extensive pump systems and raising roads further above sea level. But less affluent areas do not have the financial resources to fight the inevitable over the next century. Even if they did, no sea wall or other barrier would be able to keep water from bubbling up through limestone, South Florida’s porous bedrock, as the sea level rises.

More than 25 million people in the United States live in areas at risk of coastal flooding, and these coastal areas are more than just places to live—they are key to our economy and way of life. Marine transportation of goods, offshore energy drilling, seafood cultivation, mineral extraction, tourism, and other coastal activities are integral to the nation's economy, generating more than half of the national gross domestic product (GDP). Coastal areas also include key military and naval bases.

Ocean levels are projected to rise another one to four feet over this century. The precise number depends on the amount of global temperature rise and polar ice sheet melt.