Cross-posted from Cool Green Science.
Want to know how climate change might affect a seashore near you? Look at what it’s already done over the past 20 years to a stretch of the Florida Gulf Coast, according to a pathbreaking new study published in the journal Climatic Change.
Sea-level rise along the Waccasassa Bay area (90 miles north of Tampa) is already picking winners and losers in nature there — and the losers include the habitat the iconic Florida black bear and the bald eagle depend upon. People up and down Florida’s Gulf Coast might soon suffer, too, if sea-level rise destroys the coastal wetlands that produce world-class sport fishing and protect cities from storm surges.
Image: Dave Sag
But will these losses continue? And what can anyone do about them? Laura Geselbracht, senior marine scientist with The Nature Conservancy and lead author of the study — one of the first to test a sea-level-rise model using existing data from the past — gives some answers below.
Q. Why is sea-level rise such a big deal for Florida?
A. Because so much of the Gulf Coast here is under 4.9 feet in elevation. If the Earth experiences 3.3 feet of sea-level rise over the next 100 years — and that’s the most recent “moderate” scenario projected by the Intergovernmental Panel on Climate Change — that will mean very substantial change for Florida, not only to our coastal wetlands and natural systems, but also for people who live along the coast.
Q. The Waccasassa Bay area is one of the best places in the world to study sea-level rise — why is that?
A. First, it isn’t very populated. So you can really study the effects of sea-level rise without having to worry about development getting in the way.
Second, there have been 20-plus years of field studies done there, and you can very clearly see over that period how sea-level rise has affected that habitat. You can see where coastal forest has transitioned into salt marsh and tree islands. When you go out in the field, you come across tree trunks all over the place in the salt marsh. The habitats are changing fast, and it gives us a glimpse of what will happen in areas that aren’t as low-lying.
Q. So who’s winning and who’s losing in this race against sea-level rise?
A. We were really surprised to find that it’s not the salt marsh — which is closest to the water’s edge — that has changed so substantially. It’s actually the coastal forest, which is set back from the salt marsh. So very small, even modest changes in sea-level rise will have a fairly significant impact on the coastal wetland systems, quite a ways back from the coast. That means that, where development does exist, it will get in the way of coastal wetland systems that are trying to transition to higher elevations because of sea-level rise.
Q. About that transition to higher elevations … what’s going to happen in the future to these coastal habitats, according to your model? (I might add that you plugged the 20 years of data into the model you’re using, to see how accurately it would predict what actually happened … and it was very accurate.)
A. The predictions vary with time and with which sea-level-rise projection you use. In one 25‑year period, tidal flats and salt marsh might do well, but in the next 50 to 100 years, those habitats may be squeezed out against either higher elevations, inappropriate soil types, or coastal development. But coastal forest almost completely disappears in our 3.3-feet sea-level rise scenario.
Q. How are species that depend on the forest going to be affected? Is there anywhere for them to go?
A. Coastal forest supports some of the larger species that we all can relate to, like the Florida black bear. There is a particular population in the Waccasassa Bay area that is a very threatened population. So, as their habitat there gets more fragmented, as large swaths of it disappear due to salt water intrusion, they may not have enough room to forage and do the things that bears do, and they might ultimately die out.
Another is the bald eagle. A lot of people think, “Well, can’t they just fly to some other trees?” But those other coastal forest areas are already occupied by bald eagles, so their populations will be diminished in that area because of the loss of coastal forests. There’s a whole suite of other species that are associated coastal forests that would be impacted as well.
Q. Okay, but that’s bears and eagles. Why should people care, outside from caring about bears and eagles?
A. These effects are important anywhere along the coast. Some low-lying communities along Florida’s Big Bend Coast are going to be very vulnerable — if the coastal wetland systems retreat around those communities, it will leave some of them as islands.
And coastal wetlands are tremendously productive areas for fisheries, including things like shrimp, crab, and the majority of the wonderful sport fish that Floridians and a lot of visitors like to catch.
Finally, these coastal wetland systems help provide protection from storm surges. The marshes act like sponges — they can absorb some of the flooding that might otherwise ensue from a tropical storm, and they can also buffer the storm surge. If those wetlands disappear and become diminished, then the impacts from the storms to coastal communities would be greater.
Q. Sounds dire. So how should urban planners prepare?
A. In a couple of ways. First, it’s really important to maintain the freshwater flows into our systems, whether from rivers, overland flow, or aquifers. When you reduce those flows, your coastal wetlands retreat faster.
Second, development. It doesn’t make sense to build in areas to which coastal wetlands will need to transition. Understanding those transitions over time can help shape where you allow development or discourage it, or even help it retreat over time if that’s possible.
And third, keep our existing natural systems healthy. Transitioning of habitats in and of itself is not a bad thing, but if that change encourages a lot of invasive species that our natural species cannot access or utilize, then that could be a very bad thing. So proper land management — like prescribed fire and invasive control, along with preventing diking and ditching of our coastal wetlands to stop salt-water intrusion — are all really important.
Q. Are local communities on the Florida Gulf Coast listening to these messages?
A. We’re finding that, while some communities and local planners
are becoming aware of sea-level rise, so far a lot of communities aren’t really doing any planning. But we think they will. This research is very powerful. The information helps you understand how your whole coastal system is connected, and how the human system can be shaped to help protect natural systems, which in turn helps protect people. So The Nature Conservancy is trying to help educate local governments and regional planning councils about these types of changes and how patterns of building might change under this improved understanding.