South Florida is a land of contrasts, where high-rise luxury condos tower over the alligator-tangled Everglades.
Thousands of years ago, when people first arrived in Florida, they found a much wider, drier landscape populated by mastodons and giant ground sloths. Starting about 6,000 years ago, Florida’s climate started getting wetter, ultimately giving rise to the Everglades.
Sea level rise now is threatening to change the state’s coastline yet again and turn swamps and condos back into coral reefs.
North America’s First Snowbirds
The Florida Peninsula sits atop the Florida Platform, a piece of the African tectonic plate that was sheared off during the breakup of the supercontinent Pangea back when dinosaurs roamed the Earth. This platform sat underwater for eons, gradually encrusting a thick layer of limestone from compacted shells of sea creatures. At the height of the last ice age, when much of the world’s freshwater was frozen in ice caps and glaciers, sea levels were much lower and the Florida Platform was high and dry, exposing about twice the landmass we see today.
The first humans are thought to have reached Florida around 15,000 years ago. Some of the oldest pieces of evidence for mastodon kills in North America have been found in Florida, pulled from the watery depths of sinkholes by scuba-diving underwater archaeologists like Jessi Halligan, based at Florida State University in Tallahassee.
“Florida is pretty far from the initial point of entry into the Americas, no matter which peopling of the Americas model you follow,” Halligan told Earth magazine in 2017. Some archaeologists think that ancestors of the first Floridians may have followed the Pacific Coast to Central or South America and across to the Gulf of Mexico. Others think the peopling of the Americas was primarily overland from the western Arctic.
After humans arrived in Florida, they coexisted in a savanna-like landscape with megafauna including not only mastodons but also giant ground sloths, saber-toothed cats, and dire wolves, before these species went extinct around 12,600 years ago.
As the Ice Age came to a close, sea levels rose by as much as 100 meters. Florida flooded, and not just along the coasts but also from underneath: Florida’s limestone bedrock is water-soluble and very porous. This shallow water table is what feeds the Everglades, a 100-kilometer-wide slow moving river that flows over and through southern Florida’s limestone shelf, north to south from Lake Okeechobee through Everglades National Park and into Florida Bay.
Lost in the Scarred Everglades
Today the Everglades are a unique tropical wetland teeming with wildlife—over a million alligators, 400 species of birds, 80 species of mosquitoes, 34 species of snakes, and between 100 and 200 Florida panthers, one of the most elusive mammals in the world.
People have been trying to carve out a place for themselves in the Everglades since 300 CE, when the first canals were built by the Ortona, Calusa, and Tequesta people to connect inland villages to coastal trade routes. In the late 1800s, the first large-scale canal systems were built to drain the swamp for agriculture. These efforts fundamentally changed the hydrology of the Everglades by interrupting the flow of water.
I once got lost in a maze of roads and canals constructed in the 1960s to turn 60,000 acres of densely forested swampland into the largest subdivision in the country. After cutting 1,400 kilometers of gravel roads and nearly 300 kilometers of canals, and staking off a vast grid of 2-acre lots, the place proved uninhabitable, in large part due to the year-round mosquito population. In 1985, the Save Our Everglades campaign purchased over 17,000 vacant lots to help create Picayune Strand State Forest.
I had planned a 5-kilometer loop hike on the Sabal Palm hiking trail, but the simple line-drawing map I had picked up at the trailhead was no match for the maze of old roads, unmarked paths, and animal trails running through the dense palm forest, where a panther could pass within inches without notice. Once ravaged by humanity, the swamp has returned with vigor but still bears scars.
At a critical junction, I realized I had completely lost my bearings and suddenly felt like I was treading water in the middle of the ocean. Rattled, I decided to return to my car the way I had come instead of finishing the loop—but there were more intersections on the way back than I had noticed on the way out. Then, just as I was starting to feel hopeless, I was saved by a faded blue arrow on a tree that pointed me down a narrow trail that brought me back to the parking lot.
But the adventure wasn’t over. On my atlas (this was before I had a smartphone), it looked like I could drive west on the main gravel road and come out near the city of Naples. But the gravel road got progressively rougher, and soon I found myself lost again in a maze of unmarked roads and intersections, half full on gas but low on drinking water.
I dug out my trusty, old-fashioned compass and steered west until I came out on the first paved road I’d seen in hours. Scrawled across it in faded spray paint were the words Everglades Boulevard. It was an unsettling lifeline: Drug runners were alleged to use this abandoned road as a landing strip for small planes. Eventually, once again following a lifeline of faded arrows, Everglades Boulevard delivered me to the bright lights of Naples.
On geologic timescales, Florida may prove to be one of the more ephemeral landmasses on Earth. In the past 100 years, sea levels have risen by about 25 centimeters, mostly due to thermal expansion of the ocean. Miami and Fort Lauderdale are already seeing flooding during high tides.
In the next 30 years, sea levels are expected to rise another 43–78 centimeters, according to conservative estimates from the National Oceanic and Atmospheric Administration. Harold Wanless, a geologist and climate scientist at the University of Miami, told me that “sea level rise is speeding up” and sea levels could rise by as much as 4.5 meters by the end of the century, drowning all of southern Florida including Miami and the Everglades.
“So far, sea level rise has seemed gradual, but the geologic record tells us that’s not always the case,” Wanless said. Around 4,000 years ago, when the Florida Platform was being inundated, paleorecords show that water levels surged by as much as 15 meters in a few hundred years in a phenomenon known as a meltwater pulse.
“South Florida has always been a risky place to live,” Wanless said. But after 15,000 years of human habitation, in a few generations we may witness its return to the sea.
—Mary Caperton Morton (@theblondecoyote), Science Writer