Twice a day (most of the time, in most places), the ocean rises and falls in a process we call the tides. If you build near the coast you have to take that into account; otherwise, a house that’s dry most of the time, might not be when high tide comes. It’s called “tidal flooding” — because it happens even when there’s no storm, no wind, no rain — just high tide.
Of course people avoided that, by making sure buildings were high enough above sea level. The problem is that today, sea level isn’t what it used to be. It got higher because of man-made climate change (global warming), now high enough that in locations all up and down the east coast of the U.S., tidal flooding is a regular occurence. It didn’t used to be — but now that sea level has risen, tidal flooding is a problem that won’t go away. South Florida has been hit especially hard.
Not all tides are equal. Twice a month (around new moon and full moon) they’re higher than average (called “spring tide”), so that’s when tidal flooding is more likely to hit. Every year the tides are exaggerated during October (and to a lesser degree, during September and November), and when spring tide happens in October we get what’s called king tide. That’s when tidal flooding is most like to hit.
Although we are sure that the planet is heating and the sea is rising, the future progress of climate change is hard to predict. The tides, however, are easy to predict (in most locations). We can do it for south Florida. By the way, when I say easy I mean that we can do it reliably and with impressive accuracy — but unless you love fancy math, actually doing it isn’t what most people would call “easy.” I love fancy math.
Fortunately, we’ve kept good records over the years with tide gauges. Here’s the highest height of the tide in Key West, FL, for each day from 1913 through 2018 (data from the Joint Archive for Sea Level at the University of Hawaii sea level center):
The tallest spikes — when sea level reached its highest peaks — aren’t due to tides but to storms. Big storms bring storm surge, when the flood waters invade the land. But most of the spikes aren’t from storms, they’re from king tides. Nowadays global sea level is high enough that they too can bring the flood waters.
I took these data and computed two parts of it. First, is the global warming signal: a rise over time, sometimes faster, sometimes slower, but steady and “smooth” (compared to other variations). Second, is the tide signal itself. There are other influences, particularly storm surge from all those storms, but for now, let’s leave out those other factors and compute just the combination of sea level rise and the tides (those interested in the mathematical details will find some of them here). I get this:
It’s clear to see the overall rise over time; that’s sea level rise from man-made climate change. It’s also clear to see the spikes that happen every year; that’s king tide. King tide is a lot higher now than it used to be, and that’s why so many places are suffering from tidal flooding.
I took the present behavior, of both sea level rise and the tide, and projected what it might be doing in the near future in south Florida. Here is how the high tide level will change, including the effect of sea level rise continuing at 3 mm/yr. Note that it’s probably going faster than that already — my own analysis suggests the present rate is more like 5 mm/yr — and will continue to accelerate. But let’s just see what happens with steady sea level rise at a modest rate (combined with the tides of course). I get this:
Here’s a close-up on the years 2000-2020:
Now it’s evident that even though sea level rises, the year’s highest tide also depends on the tide! The height of king tide varies from year to year, even without sea level change, because it depends on how the sun and moon are positioned relative to each other — which of course is always changing, but is predictable.
Note the peak labelled “2016” — it shows that 2016 was a bad year for tidal flooding because that year’s king tide was especially high (tidal flooding hit all up and down the U.S. East coast, including Maine). The peak labelled “2018” shows that it wasn’t as bad a year as 2016. The danger in such occurences is that it lulls Miami residents into complacency, because it makes them believe that they can deal with the issue using slow measures over time.
But the peak labelled “2020” shows that next year will probably be the worst year ever for tidal flooding in south Florida. King tide will hit in October — just before we go to the polls to vote in the 2020 presidential election. Miami will be hit HARD. Trump may try to claim he has been leading the fight against climate change and sea level all along — because outright lies are his way of doing things. But this time, the damage will be so immediate and so unavoidable, and Trump’s record of denial is so vast, that in Florida, even the Trump-suckers probably won’t believe him.
As for independent and undecided voters, when the king tide hits in October 2020, I hope the democrats hold rallies all around Florida talking about climate change. Trump will go down in flames — which is our best chance, as a nation, to avoid going down in flames.
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