Cuban scientists project that rising sea levels will damage 122 Cuban towns or even wipe them off the map. They also say beaches will be submerged, water sources tainted and croplands rendered infertile. In all, seawater will penetrate up to 1.2 miles (2 kilometers) inland in low-lying areas, as oceans rise nearly three feet (85 centimeters) by 2100.

Those frightening calculations have spurred systemic action. Cuba's government has changed course on decades of haphazard coastal development, which threatens sand dunes and mangrove swamps that provide the best natural protection against rising seas.