Warm sunshine and sandy beaches make southFlorida and its crown city, Miami, a haven for tourists, but the area is increasinglyendangered by sea level rise, experts said Tuesday.During a special Senate hearing held in Miami Beach, Senator Bill Nelson describedsouth Florida as "Ground Zero" for climate change and its threats to coastalcommunities.The perils for Miami are particularly concerning because it has the most assets atstake in the world in terms of assets like homes, beachfront hotels and businesses,according to the World Resources Institute, a global research firm.Not only is there $14.7 billion in beachfront property, but Miami is also home to theworld's fourth largest population of people vulnerable to sea level rise, the WRI said.Nearly 20 million people live in the entire state of Florida, and about three quarterslive on the coast, said Nelson. - Waters rising -The waters around south Florida are rising fast. The Florida coast has already seen12 inches (30 centimeters) of sea rise since 1870. Another nine inches to two feet (23 to 61 centimeters) are anticipated by 2060, saidthe WRI.Miami is located just four feet (1.22 meters) above sea level."We are on this massive substrate of limestone and coquina rock which is porousand infused by water," Nelson said at the hearing, held on the 44th anniversary ofEarth Day."You could put up a dyke but it is not going to do any good," he added, describingthe land beneath Florida as "like Swiss cheese." "So we have to come up with new, innovative kinds of solutions," said Nelson, aDemocratic senator who was born in Miami.The mayor of Miami Beach, Philip Levine, said residents are commonly seen wadingthrough knee-deep waters to get to their homes and businesses during high tidesand floods."This reality is not acceptable and it is getting worse," said Levine.Officials are investigating the use of tidal control valves and new water pumps toimprove drainage, with three pumps planned for installation before October's hightides, Levine said."We are projecting the cost of being anywhere from three and four hundred milliondollars," he said.Discussions are also under way on urban designs and city plans that could betterequip the area for rising sea levels, he said.- High costs Climate change may bring more severe weather, warned Piers Sellers, deputydirector of the science and exploration directorate at NASA."What does all of this mean to Florida? By the end of the century the intensity ofhurricanes, including rainfall near the centers of the hurricanes, may increase,"Sellers said."Rising sea levels and coastal development will likely increase the impact ofhurricanes and other coastal storms on those coastal communities andinfrastructure."Fred Bloetcher, a professor of engineering at Florida Atlantic University, said sealevel rise is a present threat to "nearly six million Floridians, their economy andlifestyle, 3.7 trillion dollars in property in southeast Florida alone and a $260billion annual economy."Meanwhile, insurance companies are still unprepared to cope, said Megan Linkin, anatural hazards expert at Swiss Re Global Partnerships."Presently I know of no insurance or reinsurance company that directly includes therisk of climate change," she told the hearing."And that is because our product is typically contracted on an annual basis, and inthat time period the impact of any climate changes -- including sea level rise -- aretoo small and insignificant and without scientific consensus to responsibly includein our model and approach."  Despite the risks, tourism continues to boom in Florida.In 2013, 14.2 million visitors spent nearly $23 billion in the Miami area, said WilliamTalbert, president of the greater Miami Convention and Visitors Bureau.Last year also marked the first time in history that more visitors came from foreigncountries than from the United States, he said.