Forget climate change histrionics; the seas around Florida have been rising for eons. How quickly they rise over the next 100 years, however, will pose a host of challenges for the state — and reshape Florida in the years to come. Timing is everything.

Florida has 18,000 years of experience with sea-level rise. At the peak of the last glacier cycle, when seas were far lower, you could hike south from the site of presentday Tampa to Key West. The beach sat 100 miles to the west of present-day Fort Myers.

Regardless of how you feel about climate change, Florida’s experience since the peak of the Ice Age shows unequivocally that the sea has been rising ever since that Tampa-Key West hike was possible. The bulk of the rise occurred in the first thousand years after the Ice Age peak. In the past 100 years, the National Oceanic and Atmospheric Administration reports, the sea level rose 9.5 inches at a reliable Key West gauge.

Sea-level rise overeons is a yawn. It becomes a problem — particularly for a peninsular state with 20.5 million people — when it occurs rapidly. And later this century, a host of governmental and academic researchers project it will pulse dramatically higher and faster because of a combination of Mother Nature’s workings and, mostly, man-made causes.

Initially, the dramatic pulse will have little to do with melting glaciers. Water expands as it warms, and the seas are warming. Later, in the last half of the century, as ice-melt accelerates in Greenland and Antarctica, sea-level rise will intensify.

Nothing will prevent it.

The uncertainty is exactly how much and when the sea will rise. Different projections by three respected organizations show a nearly 50-inch spread by 2100. The projections, if anything, err on the low side, scientists say. “I think a lot of the public doesn’t understand that scientists by nature are conservative,” says oceanography professor Gary Mitchum, of the University of South Florida’s College of Marine Science. “The actual projections we’re making are probably on the conservative side.”

Natural changes come into play. Arnoldo Valle-Levinson, an oceanographer in the civil and coastal engineering department at the University of Florida, is a true believer in human-caused climate change and its effects, but in research published in Geophysical Research Letters this summer he and other UF researchers found that a rise of four to six inches in sea level along the U.S. southeastern seaboard since 2011 involved natural atmospheric pressure variations superimposed on those related to global warming. The sea-level rising “hotspot" might relate to some of the Indian River Lagoon’s pollution troubles and explain the spate of “sunny day” flooding on Miami Beach.

Valle-Levinson says, however, that it’s wrong to conclude that human-caused sea-level rise is a myth. Rather, it’s better to conclude that human-produced rise will compound what nature does.

Government, in responding to the projections, is already changing how it operates, and the private sector will have to follow government mandates. In 2012, the state began including sea-level rise in community planning and began guiding localities in creating “adaption action areas” to focus on infrastructure — tidal valves, roads, bridges, seawalls, drainage systems, for example — that’s susceptible to surges, high tides and sea-level rise. Fort Lauderdale, in its last report, listed 42 projects in 17 city areas for improvements. To withstand sea-level rise and storm surges, Miami-Dade is spending $50 million as part of a $600-million upgrade of a wastewater plant on Virginia Key in Biscayne Bay to elevate electrical and control components some 20 feet above sea level. (The existing facility is already 10 to 14 feet above sea level.) The county expects the plant to be usable for another 50 years, by which time a new plant inland will add resilience to its system.

In this series, Florida Trend attempts to present what’s likely to happen over 25-year chunks of time, and the issues that rising sea level will present for the state during those periods.

Trend is using the sea-level rise projections released in 2015 by the South Florida Climate Change Compact, a joint effort of south Florida counties. Its “unified” projection, applicable around all of Florida, actually encompasses three projections — low, moderate and high — to guide development. The projection’s baseline is 1992. Trend, instead, has used the projections’ 2017 estimates — seas up 3 to 6 inches from 1992 already — as a baseline.

The sea-level rise reflected in the projections is “locked in” — guaranteed, researchers say, by inputs such as emissions already in the global environment. It’s irreversible no matter what happens with emissions going forward.

Big changes appear in store for Florida. At first look, it appears that the state that went in a century from a water-logged afterthought to the nation’s third-most-populous could see the process reverse this century as land disappears. Rising insurance premiums, business interruptions from flooding and repeated flooding of homes and streets will, over time, force many Floridians to either relocate within the state or leave.

Costs will rise as government tries to keep drainage systems ahead of rising seas and freshwater ahead of saltwater intrusion — costs that will be too high for some areas to be saved. “Some hard decisions are going to have to be made,” says economist David Letson of the University of Miami’s Rosenstiel School of Marine & Atmospheric Science.

Florida has proven itself to be adaptable: It strengthened building codes after Andrew in 1992 and has rebuilt its insurance markets after Andrew and subsequent storms.

“Look, we came here 100 years ago. It was a miserable place,” says Miami-Dade Chief Resilience Officer Jim Murley. “The only way we learned how to live here was by managing water, and filling, and taking advantage of high land.” He believes the future entails accepting the science, collaborating, deciding what areas to protect, what to let go and learning to live with the water. Says Murley, “It’s a viable way to go forward.”