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The rising tide of climate change

Mar 29, 2016
by Bobbie Stewart

With weather growing more extreme and temperatures rising steadily, the topic of climate change has taken center stage, including at Flagler College where this year’s Ideas and Images speaker series focused on climate change and its impact on coastal communities. Flagler’s Dr. Matthew Brown, an oceanographer by training, has participated on several major oceanographic research trips, traversing the oceans surrounding Bermuda, Tahiti, Iceland and Antarctica. The assistant professor, who teaches a course on Global Climate Change, recently sat down with Flagler College Magazine to discuss the implications of sea level rise on area ecosystems and why gradual change may prove the most damaging.

Below is the full, expanded version of the article featured in the magazine.

Question: What are the biggest climate change concerns facing coastal Florida?

Answer: I’d say sea level rise is the most pressing issue we face here in Florida. Ocean acidification (the decrease of normal, healthy ocean pH levels) is, in my opinion, the most alarming thing happening with regard to marine chemistry. Sea level rise is physical in nature as it has to do mainly with the fact that as the ocean warms, it naturally expands and sea level increases. Ice loss is also part of the increase as well but in the last 30 years thermal expansion of the ocean has been the major contributor to sea level increase. Here along the east coast of Florida, sea level has been increasing at faster rates than the overall global average, and this will have significant impacts on coastlines, our salt marsh ecosystems and our coastal infrastructure moving forward.

Q: What can we expect, in term of how we experience sea level rise, in the St. Augustine area?

A: Ten or 15 years from now, will you see water pouring into the street on San Marco (Avenue)? No, probably not. Will there be catastrophic sea level rise in that time frame? Likely, and hopefully, not. Will you see more days of nuisance flooding (flooding that causes public inconveniences, such as road closures and overwhelmed storm drains)? Very likely. A full moon and associated high tides, wind, all that combined, and then you you throw sea level rise into mix, and you can face serious flooding. In the Davis Shores neighborhood, behind the Conch House, if they get two to three days of a hard north wind, at high tide, there’s already water in the streets. This type of nuisance flooding is occurring more frequently and sea level rise will add to this. With regard to the ice melt of large ice sheets, historically there has been a pretty slow, sustained rate of ice loss, but a big question is ‘What starts happening when large sections of ice sheets start collapsing?’ "What if the major ice sheets (West Antarctic Ice Sheet and Greenland Ice sheet) begin to experience increased rates of melting and subsequent ice loss?" That’s one of the big worries. Currently, rates of sea level rise along the east coast of the U.S. are on the order of less than one inch per year so there have not been dramatic visual displays of sea level rise along our coast. However, that number will likely increase significantly as we move into the future.  The big question is: By how much?  Some very recent scientific studies show estimates as high as an additional eight to 10 feet of sea level rise by 2100. Whether the increase is two feet or four feet or 10 feet, this is something that Floridians need to be preparing for.

Q: But isn’t that part of the problem, that because you don’t see the dramatic shift, you don’t think it’s actually happening?

A: There was a really well done piece in National Geographic (March 2015) titled “The War on Science” and part of that had to do with global climate change. The article highlighted the fact that roughly 95 percent or more of the scientific community agrees that human beings have had a significant contribution to the warming of our atmosphere and oceans over the last 40 years. Yet only about 30 percent of the general public thinks climate change has anything to do with human beings, and many still doubt it’s even happening at all. The article discusses this disconnect and illustrates the impact that your societal/political/familial camp can have on your views on climate change. Basically, your friends/family/political orientation can be so entrenched against climate change that you bend into the same line of thinking without regard to actual scientific evidence presented to you. Sea level rise is a tough issue to deal with as the effects are not so immediately obvious. With ocean acidification you can stick a pH sensor in the ocean, and you’re seeing a change — it’s visible and the effects are measurable. The effects on clams, oysters, and corals are measurable and real. You can look at tidal charts from Mayport Poles in Jacksonville and Charleston and see that sea level rise is going up and up and up. But you’re talking about changes on the order of millimeters. It’s not like five years ago, there was five feet less of water and now we are inundated. It’s hard to see the millimeters with the naked eye, but just because you can’t see it doesn’t mean it’s not happening.

Q: Are the ecosystems of our waterways necessarily damaged when water rises — whether it’s a natural occurrence or not?

A: If the sea level rise is gradual enough, there’s a process that takes place called accretion, which is a build up of sediment underneath a salt marsh that allows it to keep up with a relatively slow rise of sea level, but if you have a dramatic increase of sea level in a short amount of time, then it can’t keep up with the rising water.  If the rates of ice loss from large ice sheets such as the West Antarctic Ice Sheet or Greenland ice sheet accelerate, this could have very negative impacts on the abundant salt marsh, mangrove and oyster beds that make this region so diverse and so healthy in terms of biodiversity and water quality. It should be noted that these ice sheets have enough stored in them as ice that, if they were to completely melt, would raise global sea level by over 150 feet. This would not happen anytime soon and may never happen but the uncertainty associated with the rate of ice loss of the major ice sheets should be cause for concern. In the last 40 years, it is estimated that we have lost nearly 35 percent of the summer sea ice in the Arctic Ocean as the ocean and atmosphere has warmed in that region.

Q: And what about the Floridan aquifer (an underground reservoir of groundwater)? Will climate change and sea level rise affect that?

Yes, that’s another issue — saltwater intrusion. Our drinking water comes from the Floridan aquifer, a very large underground reservoir of water that took a very long time to form. As withdrawal rates of water from this aquifer increase with the growing populations both in northeast Florida and the southeast U.S., as sea level rises along the coast and the level of water in the aquifer decreases, salt water can infiltrate into the aquifer system. This is already happening in northeast Florida and there has been a documented increase in the salinity of our aquifer over the last couple decades. The salinity of our water supply slowly starts to creep up and up. If you think of farmers watering crops, such as plants, grasses can tolerate some salt, but there is a limit to what plants can tolerate. We have students do experiments where they’re exposing wheat to different amounts of salt water, and even with a minimal amount of salt added, there can be a detrimental effect on plant growth.

Q: What’s the current state of the Floridan aquifer. Is it “healthy?”

A: Yes, the water quality is healthy yet the aquifer has a finite amount of water. It is really a non-renewable resource. It replenishes from rainfall naturally, but the problem is the replenishment compared to society’s withdrawal rate doesn’t match. We’re pulling water from that aquifer way faster than it can keep up.

Q: Let’s talk about mangroves. Over the years, locals have noticed the arrival of these trees in the salt marsh, which are typically more common in southern Florida. Is this encroachment natural, or due to warming temperatures? And what impact does this have on northern Florida’s ecosystems?

A: Mangroves are a fairly freeze-intolerant species, meaning that when the temperature dips below freezing for even a short period of time, the mangroves have a hard time surviving. St. Augustine for some time has been close to the northernmost limit for the northern extent of mangroves in Florida, but now we are seeing mangroves move even further north. In the last 30 years the cover of mangroves along the coast in our region has roughly doubled. While this is not necessarily due to average temperatures increasing with time, it has more to do with a decrease in the frequency of significant freeze events in northeast Florida. As mangroves increase in cover in our region, we could be shifting from a salt-marsh dominated coastal ecosystem to one that becomes dominated by mangroves. Both salt marshes and mangroves are efficient mechanisms of absorbing excess nutrient input into coastal regions as well as providers of ecosystem services such fish nurseries and dampeners of wave energy. Both mangroves and salt marshes will begin to compete for the same resources and we could see shifts in ecosystem community structure as time moves forward.

Q: How would you respond to those people that claim that these changes are a part of the natural evolution of things — that plants, animals, ecosystems either survive or they don’t, that pH sea levels have a history of fluctuating?

A: It is true that climate changes naturally in the absence of humans. Sea level has risen and fallen and pH levels of the ocean have gone up and down long before humans were in the picture. However, the rates of carbon emissions to our atmosphere, the rates of warming that we are seeing on our planet, the rates of sea level rise and the associated impacts on biodiversity we are currently observing are very significant when compared to past estimates based on the geologic record. In some cases, the oceans and atmosphere are undergoing changes we haven’t seen on the order of millions of years, and this is happening over the time scale of decades. A lot of these changes are happening on such a short time scale and it is unknown if species will be able to adapt to these changes. It really has to do with how fast a number of these changes are occurring.  A number of these changes also correlate very well with the exponential growth of the human population our planet is experiencing.

Q: If the effects of climate change continue to worsen, what are we looking at?

A: If you take all the major stressors on the ocean right now, some of which are climate-related — ocean acidification, ocean warming and coral bleaching, sea level rise — and some of which are more society-driven, such as increased fertilizer use in development (which leads to eutrophication, the excessive loading of nitrogen and phosphorus into coastal waters), associated harmful algal blooms and low-oxygen zones, plastic pollution, overfishing of major fish stocks…It is not a pretty picture. The ocean is really being negatively stressed. We’re likely looking at a less diverse, less well-functioning eco-system, fewer seafood options and drastic changes in ocean ecosystem structure — fewer coral reef ecosystems, fewer higher trophic level fish, a decrease in oceanic productivity and a significant loss of biodiversity. In some cases where major fish species are being overfished, jellyfish and stingray populations are booming.  There are studies that estimate that over 80 percent of the oyster reefs worldwide have been decimated due to poor water quality, disease and over-harvesting. Both salt marshes and oyster reefs help remove nitrogen and certain pollutants, and when you threaten the salt marshes or oyster reefs, you’re going start pulling those things out of the equation. They are natural filtering mechanisms to our coastal waters and provide a huge number of ecosystem services yet these services are in jeopardy of being lost.

The problem is, there are so many unknowns. We don’t know exactly how organisms are going to respond to sea level inundation. The thing with a good science project is that you have a control and you have an experimental group. The problem with climate change is there’s no control. We’re the control group and experimental group all wrapped in one.

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