Sea Level Rise Doubles Risk of Catastrophic US Flood Three reports say rising seas endanger continental US By Kevin Spak, Newser Staff Posted Mar 14, 2012 8:04 AM CDT 18 comments Comments People walk through flood waters in their Fort Lauderdale, Fla. neighborhood in this Oct. 31, 2011 file photo. (AP Photo/J Pat Carter) (Newser) – Coastal states are now twice as likely to experience a so-called once-in-a-century flood by 2030, thanks to a global warming-fueled rise in sea levels, according to a trio of reports released today. Census data shows 5 million people are in the danger zone, particularly in cities, where many people live below the four-foot mark. South Florida in particular has 106 such municipalities and is basically "indefensible," because it's built on "bedrock that's like Swiss cheese," Ben Strauss, author of one report, tells Reuters. Global sea levels have risen 8 inches since 1880, and are projected to rise between 2 and 7 feet this century, fueling storm surges. In some places, the chance of a catastrophic flood is actually triple, and some spots in California may experience severe floods for the first time. "Sea level rise is like an invisible tsunami," Strauss tells the New York Times. "We have a closing window of time to prevent the worst by preparing for higher seas."