National Geographic : 2013 Sep
56 national geographic • September 2013 says Jayantha Obeysekera, the chief hydrological modeler at the South Florida Water Manage- ment District. “At times now the water level in the sea is higher than the freshwater level in the canal.” That both accelerates saltwater intrusion and prevents the discharge of flood waters. “ The concern is that this will get worse with time as the sea-level rise accelerates,” Obeysekera says. Using fresh water to block the salt water will eventually become impractical, because the amount of fresh water needed would submerge ever larger areas behind the control structures, in effect flooding the state from the inside. “With 50 centimeters [about 20 inches] of sea-level rise, 80 percent of the salinity-control struc- tures in Florida will no longer be functional,” says Wanless. “We’ll either have to drown com- munities to keep the freshwater head above sea level or have saltwater intrusion.” When sea level rises two feet, he says, Florida’s aquifers may be poisoned beyond recovery. Even now, during unusually high tides, seawater spouts from sew- ers in Miami Beach, Fort Lauderdale, and other cities, flooding streets. In a state exposed to hurricanes as well as rising seas, people like John Van Leer, an ocean- ographer at the University of Miami, worry that one day they will no longer be able to insure—or sell—their houses. “If buyers can’t insure it, they can’t get a mortgage on it. And if they can’t get a mortgage, you can only sell to cash buyers,” Van Leer says. “What I’m looking for is a climate- change denier with a lot of money.” Unless we change course dramatically in the coming years, our carbon emissions will create a world utterly different in its very geography from the one in which our species evolved. “With business as usual, the concentration of carbon dioxide in the atmosphere will reach around a thousand parts per million by the end of the century,” says Gavin Foster, a geochemist at the University of Southampton in England. Such concentrations, he says, haven’t been seen on Earth since the early Eocene epoch, 50 mil- lion years ago, when the planet was completely ice free. According to the U.S. Geological Survey, sea level on an iceless Earth would be as much Land of windmills and dikes flanked by windmills, this dike protects farmland that is almost entirely below sea level. dikes and continuous pumping keep more than a quarter of the country from reverting to swamp or open water. The Netherlands: Low Country, Long View flevoland for nearly a thousand years the dutch have been reclaiming land from the sea—and occa- sionally losing some. a catastrophic flood that killed more than 1,800 people in 1953 spurred the country to develop the world’s most elabo- rate and sophisticated system of dikes and other defenses. the most critical structures are built to withstand a 1-in-10,000-year storm.