(CBS News) LOS ANGELES - It was reported Thursday in the journal "Science" that polar ice is melting three times more rapidly now than it was in the 1990s. So what does that mean for the rise of the seas?
The researchers, including NASA scientists, say Antarctica and Greenland have lost nearly 5 trillion tons of ice since 1992, causing sea levels to rise by nearly half an inch.
"We really didn't know that we were going to find such a dramatic speed-up," said NASA's Erik Ivins, who worked on the study.
Scientists say human activity such as burning fossil fuels is warming the atmosphere.
"Each year we are getting longer and longer melt seasons," Ivins said. "This year we had one of the longest melt seasons that we've ever seen."
Melting ice sheets now account for 30 percent of the rise in ocean levels, making flooding from storms such as Hurricane Sandy even more destructive.
Along the California coast, the ocean is expected to rise another 3 to 5 feet by the end of the century. About 3.5 million Californians live within 3 feet of sea level.
"Eventually we will be consumed by a higher elevation of the ocean," said Jefferson Wagner, the former mayor of Malibu. He said some beaches there have lost 5 to 6 feet of sand in recent years due to stronger storms and higher tides.
"These things are happening," said Wagner. "We have to realize they are happening. We're seeing it here. There's no denying it any longer."
Two years ago, wealthy homeowners along Malibu's broad beach put up an 8-foot high rock wall to protect their homes.
"It's just a matter of time until the sand is taken away from underneath this revetment, and the rocks simply start to collapse, said Wagner as he demonstrated on the beach what would happen.
The California Coastal Commission is strongly encouraging all coastal communities to have a plan in place to deal with rising sea levels.