A few feet of sea level rise, so what?
One of the reasons that rising sea level may not concern most people is that “a few feet” doesn't sound like much. What they probably don't realize is that for every foot that sea level rises, the coastline can move hundreds of feet inland; in some cases more than a mile. But it’s hard to visualize; and the amount does vary depending upon the profile of the shoreline, and its composition — such as whether it's sand or granite.
As I was driving up the coast in northern Florida a few weeks ago, I just happened to see a stunning example that illustrated the extent of our vulnerability to sea level rise. I was going from Cape Canaveral, up to Flagler Beach, a bit south of Jacksonville. Normally I would take the interstate, I-95; but I had a little extra time so I decided to take the coastal road. I crossed over the intracoastal waterway at Daytona Beach.
As I continued driving North, with the shimmering Atlantic on my right, my mind was working on the question of how to explain the vast impact of a few feet of sea level rise for a book I am writing. Based on the latest projections, by the end of this century, there could well be three or four feet of sea level rise, assuming the melt rates in Greenland and Antarctica don't get substantially worse than at present. Even by the year 2050, that could mean a foot or two of sea level rise, which at first may not sound that bad, but is indeed.
I was glancing over at the beach, which probably had a vertical rise of at least ten feet from the high tide mark, to the level of the road on which I was driving. It was easy to see how anyone might believe that a few feet, on top of the present sea level, would merely reduce the width of that gorgeous beach.
The problem, or flaw with that perception, was obvious when I looked towards my left, away from the beach. The height of the land, or elevation dropped off significantly — for a very long distance inland, perhaps a mile, in some places. In other words, behind the beachfront rise, there was a vast lowland. This coastal profile is quite common.
The illusion is that the line of sand dunes, or the elevated berm, is a continuous barrier. It's not. Every inlet, river, stream, and marsh is a break in the high coastal barrier. In fact, just a few miles earlier on my drive, I crossed a bridge over one of these inlets.
Perhaps with that visual in your mind, you can imagine what will actually happen with rising sea level. Over the years, the ocean will work its way through the point of lowest elevation, those low lying sections in the coastline — rivers, inlets, marshland. Inch by inch, the sea would creep inland, flooding the entire area behind the elevated strip of land, that now supported Route A1A, where I was driving. So, even those beaches with a steep elevated line of sand dunes, provide a false image as a barrier.
The beach profile was very visible here. The same profile exists in much of the Southeastern US, from Miami, up to the mid Atlantic region.
Another point to remember is that rising sea level compounds the damage of abnormal waves, such as in storms and hurricanes. The most recent forecasts are that we may get double the number of category 4 and 5 hurricanes in the north Atlantic over the course of this century. During such events, waves pound the coast, and cause massive sudden erosion. Often roads and seawalls are breached, causing a new opening for the sea to move inland. Sometimes it just moves millions of gallons of seawater over the seawall flooding what's on the other side. And then, that same barrier acts as a retaining wall, keeping the seawater in place.
A few feet of sea level is a big deal. Consider that in most locations, that's the amount of rise and fall between high and low tide. Check out the impact of the daily tide rise on harbors, marinas, and commercial ports; imagine doubling that. Think of all the coastal roads, canal based real estate, and large infrastructure such as airports, that are just a few feet above the current sea level.
Can we hold back the sea, and win the battle for the coast? For a limited time, in limited locations, with enough resources — “Sure.”
Long-term, as in centuries, my bet's on the ocean.