You might not be able to hire a gondolier along U.S. 1 anytime soon. But sea level rise could have portions of the Florida Keys looking a little bit more like Venice in the coming decades.

That was the message from University of Miami geologist Harold Wanless, who recently spoke about sea level rise before a packed crowd of more than 100 at John Pennekamp Coral Reef State Park. According to his report, the Keys are in some peril.

"What I am saying is, don't think about your investment in coastal areas as something that is going to be passed down to your great-grandchildren," Wanless said.

Since 1930, sea level in South Florida has risen 9 inches, an eightfold increase over the rate of the previous 2,000 years, Wanless said.

That might not sound like much, but in Key West it has been enough to transform roads that were once safely elevated a foot above the mean high tide into ones that are commonly flooded, city officials report.

To date, most sea level rise has been the result of water's tendency to expand as it warms. But experts expect sea level rise to accelerate as global warming melts the Greenland, Arctic and Antarctic ice caps. In 2007, the United Nations Intergovernmental Panel on Climate Change concluded that global sea levels will rise between 7 inches and 1.9 feet by 2100. That estimate, however, did not allow for melting of the ice caps.

As the melting of the ice sheets has accelerated, studies in major scientific journals since then have concluded that sea level could rise 5 feet or more by 2100.

Wanless last week said that even with major worldwide reductions in greenhouse gas emissions, he expects such a scenario to unfold.

"People talk a lot about uncertainty," he said. "There isn't a lot of uncertainty. It's 4 to 5 feet this century."

With an average elevation of less than 5 feet, according to The Nature Conservancy, that could mean disaster for the Keys. Low-lying neighborhoods would be largely under water.

In addition, coastal wetlands and mangrove environments would collapse, just as they have already along Cape Sable on the southern tip of the mainland.

"Miami-Dade and Broward will be diminished and risky places to live -- including all of the Florida Keys," one of Wanless' lecture slides said, in reference to a 3-foot to 5-foot sea level rise.

His speech came as skepticism of climate change science is on the rise. A recent CNN poll found that the percentage of Americans who believe that global warming is caused by humans dropped from 54 to 45 percent between the summer and December.

The decrease came on the heels of this fall's "Climate-gate" scandal, in which hackers obtained thousands of e-mails from climate change scientists at the University of East Anglia in England. In some of the e-mails, the scientists appeared to be attempting to suppress information that did not fit with their conclusions.

Wanless urged attendees at his lecture to take global warming seriously.

"If you don't buy global warming, learn about it," he said. "It is too important. Don't listen to Rush Limbaugh. He is not a scientist."

Wanless jokingly titled his lecture "The State of the Conch Republic Address" because he delivered it the same time as President Barack Obama's Jan. 27 State of the Union speech. Attendees on their way out of the lecture were convinced.

"Very informative," Islamorada resident Will Dunbar said. "I'm just going to be a grandfather. They're the ones who are going to be affected.

"They'll be the ones who'll inherit the earth."

rsilk@keysnews.com