The Shrinking Line Between Land and Sea

Written by Frank Lowenstein on . Posted in Learn
















An east wind whips Gasparilla Sound into foam. Literally. Chunks of wind-whipped water blow ashore as I unload my kayak from my car onto the sand. While I’m gathering my paddle, nautical chart, camera, and life vest from the trunk, water chunks continue to fly so I’m wet before I start. This is South Florida—a place where the lines between land, water and air are often blurry.

During the next hour and a half, I fight wind, waves, and foam-in-the-face to cross the sound (which is a bay at the north end of Charlotte Harbor) and reach the sheltered waters of smaller Bull Bay. A veritable Sibley’s Guide to Birds flies overhead—laughing gull, osprey, Forster’s tern, tricolor heron, little blue heron, great blue heron, belted kingfisher, brown pelican, spotted sandpiper, double-crested cormorant.

The landscape that feeds the air show is the shallow and productive waters of the bays. Where the seafloor comes to meet the surface, mangroves, the unique salt-tolerant wetland trees of the tropics, sprout up. Their roots trap sand and sediment, building new land around themselves an inch at a time. My nautical chart shows the mangrove islands as land, but some of the islands have literally no dry land at high tide—the mangroves rise directly from the ocean. Storm waves and boat wakes can steal away the precious sand. Over time the islands form and break apart like dancers in a Bollywood dance scene. In this case a dance floor of inches separates what we call sea from what we call land.

With climate change, the tempo of the dance is becoming ever faster. For the mangroves, oyster reefs, barrier beaches, and sea grass beds of Charlotte Harbor, the driving rhythm of change is the rising seas. Sea level has risen about a foot in the eastern US in the last 100 years, and more rapidly in recent decades than in earlier ones.  Estimates are that it may rise 3 to 6 feet more by the year 2100, with huge impacts on society and ecosystems. And as a new article in Nature Climate Change last week made clear, there’s no reason to think that sea level rise will stop in 2100.

The article examined previous scientific predictions about how much global warming would be needed to melt the Greenland ice sheet, and it found those estimates failed to take into account that as the ice cap melts, it becomes lower in elevation and thus is located in warmer air. At some point the melting becomes unstoppable regardless of how many Prius models Toyota offers. According to the new study, climate change regarded by most scientists as nearly inevitable is likely to commit us to melting the entire ice cap. But because there is so much ice in Greenland, it’ll take a long while to melt. How hot it gets (i.e. how much carbon we emit) will determine whether that melting takes hundreds of years or many thousands.

If the Greenland ice sheet melts, the oceans will rise an additional 21 feet. That’s enough to put the communities around Charlotte Harbor completely underwater. A $100 million sport fishery, the city of Fort Myers, and the iconic communities of Sanibel, Captiva and Boca Grande all would be under the waves.

The study highlights one of the most important aspects of climate science. While there is uncertainty, and while climate scientists—like the rest of us—are fallible, there’s just as much chance that those doubts will cause us to underestimate risk as to overestimate it. And the potential for damage is huge, as another study last week emphasized. This one, from Climate Central and published in the journal Environmental Research Letters, rolled out a new tool to estimate the number of homes at risk from different amounts of sea level rise. Nationwide some 2.6 million homes will be at risk of washing away in storms by 2030, with the greatest number of homes at risk in—you guessed it—Florida.

For the long term? Well, Climate Central didn’t analyze for 21 feet.

In the near term, The Nature Conservancy and partners are pursuing solutions to help keep Charlotte Harbor healthy. We’re looking to restore oyster reefs in key areas to help reduce wave heights and consequent shoreline erosion. And in deciding where to put the reefs we’re looking not just at where they originally were, but at where conditions are likely to remain suitable for the future, using sea level rise modeling (an example of which is the Conservancy’s Coastal Resilience Tool). The reefs will help protect the amazing mangroves and shorelines of the area—for local residents and visitors alike.

Frank Lowenstein is Climate Adaptation Strategy Leader for The Nature Conservancy.

Photos courtesy of Frank Lowenstein.

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Comments (1)

  • Marcia Cravens


    I’m interested in data on SWF coastal protection and sustainability. I’m especially interested in protection of our few remaining shallow vegetated productive mangrove, seagrass, oyster, clam, and tdal flats estuaries.

    Please provide links for most recent reports on sea-level rise impacts to SWF coastal areas and credible science of smart ways to reduce those impacts and protect/sustain our beaches and nature based estuaries.

    Also, what kinds of services are available from the Nature Conservancy ?

    Marcia Cravens
    FL Master Naturalist for Coastal Systems
    Sierra Calusa Group


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