Changing Seas: A View From the Florida Coast

Big Picture

This week marks World Oceans Day, so it’s a fitting time to reflect on the state of our seas from a part of the world where things have changed dramatically over the past few decades: Florida.

In the forty-some years I’ve called Florida home, my attention to the ocean has ebbed and flowed, but I’ve always taken its presence for granted; I know what it will do each season, and I miss it when I’m gone. I’m sure I’m not the only one with this mindset. Folks in every waterfront community—from Boston, to Miami, to Sacramento—took the sea for granted the moment they built a seawall and started their town just behind it. And why not? High tide was about as guaranteed as nature gets. Twice a day, like clockwork. But in Florida, things have started to change.

Warm Winds

When most people think of hurricanes, they probably think of raging winds, but that’s not what does the most damage, at least not directly. Across hundreds of miles, these tropical cyclones gather strength from warm, open ocean and push a wall of seawater—the storm surge—in front of them.

It’s tempting to believe that a warmer climate necessarily means more powerful storms (heat = energy), but so far the science on this is tentative. Hurricanes are complex climatological events that belie such a direct relationship, but some evidence suggests this may become the case, especially in the latter half of the century. But regardless of cause, the more powerful the hurricane, the more water it pushes, and when the surge arrives, this is what typically does the most damage. Timing plays a huge part in its impact, because tidal variations can be 6–7 feet or more. Thus, an eight-foot storm surge that hits at dead low tide, versus at peak high tide, can mean a town that is largely spared or completely inundated.

For this contingency, most homeowners in coastal Florida buy flood insurance, and since Florida (not Kansas) is the flattest state in the country, this makes good sense. Cost is determined by “base flood elevation”: how high your house sits above the high-water mark of a 100-year flood. However, in back-to-back seasons, storm surges from Atlantic hurricanes brought the tide very near my town’s hundred-year line twice, sparing my house by inches each time, while inundating many of my neighbors’. In all my years living in St. Augustine, I’ve never seen anything like it.

So Long to Slowly Rising Seas

How much sea level rise helped inundate coastal Florida during hurricanes Matthew (2016) and Irma (2017) is hard to know, but in the coming decades it will undoubtedly play a greater role. Globally, sea level rise is driven by two related aspects of climate change. As the earth heats up, warmer oceans cause water to expand. A hotter planet also melts large amounts of ice in places like Greenland and Antarctica. Both phenomena add volume to the planetary bathtub.  Sea level rise is hard to comprehend because it happens so slowly (.4”–1” per decade since 1900), but that rate is rapidly increasing, with sea levels projected to rise 1–8 feet by 2100.

As worrisome as this is, it’s even less clear what any one place will experience because global sea level rise is not uniform; in some places it’s even temporarily falling. Localized sea level rise can be due to human-influenced climate change combined with naturally occurring climate patterns like El Niño. The Atlantic coastline has a number of these ‘hot spots’ where accelerated rates of rise have become especially problematic. In places like Annapolis, Maryland, for example (or in the Gulf, the bayou communities of Louisiana), rising seas have already done significant cultural and economic damage.

Ecological Newcomers

It’s well known that the Sunshine State attracts snowbirds from Canada and New England who leave their icy winters behind after retirement. In fact, Saint Augustine has one of the oldest and most spectacular monuments to this winter migration, the former Hotel Ponce de Leon (now Flagler College).

But as climate change makes the cooler, northern part of Florida more like the tropics, ecological newcomers gradually make their way up from South Florida to colonize the tidal salt marshes of my part of the state. I’m not talking about retirees, of course, but new species of plants and animals, the most obvious of which, mangroves, can be seen from space.

Historically, St. Augustine was an ecological Mason-Dixon line that separated two species of saltwater flora: mangroves to the south, and marsh grass to the north. Mangroves simply aren’t hearty enough to survive the annual cold snaps that occurred around St. Augustine and points north. In my childhood, it was acres of marsh grasses that dominated the horizon until the bay became open ocean. But as the climate warms, the mangroves common farther south have gained a foothold in northeast Florida, turning salt marshes into unrecognizable ecosystems. These small trees may help buffer storm surge, but the marshes feel like a different place.

Appreciate and Adapt

As much as these changes concern me, I’m sure it’s not only coastal Florida where people are trying to anticipate what’s in store for their shores. Adapting to a warmer, wetter world is about all that’s guaranteed. As we figure out how to do this, I think it’s important to keep enjoying the oceans we love, so we no longer take them for granted. I was reminded of this recently on an early morning paddle through the marsh near my house. I had the pleasure of seeing a manatee, unusually active schools of fish, nearly a dozen sea turtles snacking on oyster beds, and near the end, either a shark or a large ray—I didn’t stick around to find out.

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