Rising sea level already eating away at Florida's coastline

By Curtis Krueger and Craig Pittman, Times Staff Writers

 March 28, 2008


Global warming is boosting the sea level along Florida's gulf coast and already causing profound environmental changes, scientists say.

• At Waccasassa State Park in Levy County, palms trees are toppling over dead as rising saltwater creeps up the beach.

• At Rookery Bay Preserve near Naples, salt­water mangroves have invaded what used to be freshwater marshes.

• On the western side of Everglades National Park, inland marshes are being replaced by seawater ponds.

"People have a hard time accepting that this is happening here," said University of Florida professor Jack Putz, who has led a Levy County research effort since 1992. Seeing the dying palms, he said, "brings a global problem right into our own back yard."

What is happening is not just a minor botanical alteration in a few isolated places. The scientists studying the phenomenon see it as a harbinger for major changes in the state's geography — submerging islands and turning swamps into open bays. Those changes alone can create a serious economic impact on businesses such as fishing.

The rising sea generally has crept up so slowly that it has been barely noticeable. In the Tampa Bay area, for instance, "we've actually seen an increase of about an inch a decade" since measurements began in the 1940s, said Holly Greening, executive director of the Tampa Bay Estuary Program.

Now, the rate at which the sea level is rising appears to be picking up speed.

The sea level's rise is often difficult to detect along urban coastlines because seawalls and replenished beaches can obscure or blunt the impact, said Mike Savarese, a Florida Gulf Coast University marine science professor.

But the changes wrought by higher seas are more obvious in wilderness areas such as state and national parks. In those natural areas, "we're seeing some real indications of a change out there," Savarese said.

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Rising global temperatures are melting mountaintop glaciers in Greenland and other cold locales, raising the world's sea level. But an even bigger factor is thermal expansion. Water, like most materials, expands as it gets warmer. So as the upper level of the ocean warms up, the water expands, pushing the sea level higher.

Florida is a good place to study the rising sea level because it's a coastal state where seas have risen and fallen for tens of thousands of years. That enables scientists to see what happened in the past and compare it to what's occurring now.

Consider the story of Little Salt Spring, a picturesque natural pool in Sarasota County. Archeologists can dive into the spring and swim down 40 feet to find ancient relics like spears and mastodon teeth. The location of the artifacts shows that 10,000 years ago, Florida's sea level was much lower — 30 or 40 feet below where it is now.

To study past sea level fluctuations, Savarese has been pulling out core samples from around the Ten Thousand Islands area of Everglades National Park. By using carbon dating, he can see how old the different layers are. It paints a clear picture of what has been happening, he said.

The sea that receded from Florida's shores thousands of years ago was beginning to come back, naturally and slowly — until the Industrial Revolution began filling the atmosphere with greenhouse gases, warming the oceans and speeding up the process.

"Prior to the 1800s, the rates are fairly constant," Savarese said. That rate varied from about 1 1/2 to 3 inches a century, he said.

But now, thanks to the warming of the planet, Savarese said, the sea level is increasing by a rate of 15 to nearly 20 inches per century along that part of the Florida coast.

As the sea rises, it changes the land. For instance, as the trees die and fall over at Waccasassa preserve in Levy County, Putz said, "you can see the forest changing to marsh."

Something similar has been happening at Rookery Bay, said administrator Gary Lytton of the state Department of Environmental Protection. Comparing aerial photos of the area from the 1920s to what's there now shows how mangroves have replaced freshwater marshes that are important habitat for a variety of bird and fish species.

"You can see an ecological shift that's taking place," he said. "We're beginning to lose freshwater wetland habitat."

One of the more surprising discoveries is what Savarese found amid the maze of marshes and mangroves that form the Ten Thousand Islands: inland tidal pools that are "growing in size and increasing in number. They should eventually come together and form a new body of water. We're creating a new set of bays inland of our own."

Should this trend continue, Savarese said, it could lead to a scenario where "the Ten Thousand Islands drown and the coastline becomes much more open. It would create a very different kind of ecology."

If that continues, Lytton sees a clear downside for the state's economy.

"Florida generates over $4-billion a year from sportfishing, and think about all the related businesses that tie in to that," Lytton said. Since those fish need those disappearing wetlands for habitat, he said, "if we begin to lose our coastal wetland ecosystems, it's going to begin to have a serious impact."

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How long will it take before sea level rise begins to cause major changes?

If you ask Harold Wanless, chairman of the University of Miami's geological sciences department who studies how the coastlines of South Florida have evolved over the past 4,000 years, he will give you one answer.

Wanless believes the rate will continue increasing until it surpasses 3 feet by the end of this century, and could even reach 5 feet. That "basically takes all of our barrier islands and makes them close to unlivable," he said.

But Wanless' predictions surpass what scientists from the U.S. Geological Survey have found so far in their studies from around the nation's coastline.

If the seas rise twice as much in the next century as they did in the last, "I wouldn't classify that as a catastrophe, putting everyone underwater, but you will start seeing major changes on our coastline," said Abby Sallenger, an oceanographer with the U.S. Geological Survey's center for Coastal and Watershed Studies.

The scientific uncertainty has left public officials unsure how to deal with the problem.

"I don't think that anybody's really pinned down numbers that make sense yet," said Ed Chesney, Clearwater's environmental manager. "You're talking 8 inches or 8 feet. & The jury's still out on that timetable."

Yet if sea levels continue rising, adapting to this new geography will require major changes in Florida's lifestyle — and soon.

For instance, Floridians should stop building houses, roads and other facilities in areas that already are prone to flooding, since they are more likely to wind up underwater, said Harvey Ruvin, the Miami-Dade County court clerk, who chairs Miami-Dade's Climate Change Advisory Task Force.

Some problems are likely to prove thornier than others, he said.

"At some point it will pose a threat to our drinking water supply. Our subterranean aquifers will get some saltwater intrusion at some point," Ruvin said.

But that point could be decades in the future, which leads to apathy now, says Robert Brinkmann, a University of South Florida geography professor.

"As a society," he said, "it's hard for us to get our hands around how we plan for sea level change when it's not on our doorstop right now."