Florida Sea Level

Since I am not an employee of the Florida state government under their science-denying governor Rick Scott, I’m allowed to say the following phrases: “climate change” and “global warming.”

I’m also able to mention those topics when discussing sea level rise. In the hope that I can annoy Florida’s science-denying governor Rick Scott by flying in the face of his denial of science itself, I’ll print the truth for all Floridians (and others) to see: sea level rise is being caused by man-made climate change, also known as global warming.


There are 11 tide gauge stations in Florida with data extenting up to (and beyond) the year 2010. Their data are freely available from multiple sources, including PSMSL (the Permanent Service for Mean Sea Level).

In order to combine the data into a single estimate of sea level changes in the vicinity of the state of Florida, we need to align them because they’re not all on the same baseline. I introduced a method to do so some time back. If we align and combine the data from these 11 stations, we obtain this:

FLcombo

These are anomalies, meaning that the annual cycle has already been removed so we can concentrate on the changes over time rather than just the seasonal fluctuations.

One of the complications inherent in monthly sea level data is that it is strongly autocorrelated. There are ways to deal with this, but we can simplify greatly, eliminating most of the autocorrelation, by working with annual averages rather than monthly. Those look like this:

FLannual

Note that I’ve plotted a solid blue line to illustrate the best-fit straight line by least-squares regression. The estimated rate of sea level rise over the entire time span turns out to be 2.05 +/- 0.16 mm/yr.

But perhaps the rate isn’t constant over time. We can fit a smooth curve, which I’ll do by my favorite method (modifed lowess smooth), giving this:

FLsmooth

The smooth departs from the straight line, notably. This suggests that indeed the rate hasn’t been constant over time. Although fitting a smooth isn’t the same as a proper statistical test of whether a change has occurred, it is certainly suggestive.

Yet those who deny the danger posed by sea level rise have a nasty habit of stating “no acceleration” while providing no evidence to back that up, and quoting rates of sea level rise based on straight-line fits to very long spans of time.

What would we find, you might wonder, if we fit straight lines to the same data set but instead of starting way back before the year 1900, we started at a later year? We expect such estimates will be less precise because they’re based on less data, but more relevant because what we’re most interested is not the average rate over the last 120 years, we want the rate now.

Let’s find out. I fit a straight line to the annual average sea level in Florida, starting with every possible start year from 1900 to the year 2000, ending with the final year. I also computed the uncertainty range. Here’s a graph of the estimated rate (as a dot) with error bars showing the 95% confidence limits:

FLrates

The horizontal red line shows the estimated rate from 1900 to the present. Note that starting at more recent years gives an estimated rate considerably higher than that. Considerably. More to the point, the 95% confidence interval excludes that older, smaller rate. This isn’t just suggestive, it’s actual evidence that the rate now is higher than it has been, in fact it’s higher than the overall rate. There’s a word for that kind of behavior: acceleration.

There are other, better ways to test for such patterns, some of which are illustrated in this post about temperature time series. Yes, I’ve done many of those tests too. Yes, I’ve done them using monthly data and proper allowance for autocorrelation rather than just using annual averages. Yes, the rate of sea level rise around Florida has shown acceleration.

It has also shown deceleration. In fact it shows a pattern of both slowdowns and speedups, just as global sea level does. By golly, there’s even published research about that. Before anyone protests that this invalidates climate models and/or theories of sea level change on which future projections are based, save yourself the embarrassment. Because it doesn’t.

As a matter of fact, the models which match best to observed data are semi-empirical models, which also happen to be the models which suggest the greatest sea level rise in the near future. If they’re correct, these models which best fit the data, then before the end of this century we are … how shall one say? … screwed.

But, those in denial will continue to shout “no acceleration” without any evidence to back that up, and continue to quote rates since 1900 or even earlier as though they were estimates of the present rate.

They’ll also make many more misleading statements, usually out of ignorance but sometimes out of dishonesty. For instance, they may trivialize the impact of sea level rises that seem small, just an inch or a few, without being aware (or admitting) that ain’t so. Even a tiny rise in sea level will, when a storm hits and the storm surge inundates the area, make the ocean creep further inland by vastly greater distances. Vastly. If you want details and evidence, there’s research about that too.

They’ll even proclaim that as sea level rises, we can just raise roads and bridges and other things, as though that’s a cheap and easy way to deal with sea level rise. Unfortunately, it doesn’t work that way. The amount of sea level rise that is expected this century is huge — it could be an entire meter or more — and will put rather large swaths of land underwater, because sea level is accelerating and will continue to do so. Unless, of course, ice melt and thermal expansion cease to be the result of temperature increase, i.e., the laws of physics cease to apply.

One would hope that they will pay attention to actual evidence, accept the results of valid statistics over “doesn’t look like it to me!”, and give the safety and prosperity of future generations a bit more priority than the profit margin of Florida’s science-denying governor Rick Scott and the uber-rich he serves. Because he sure ain’t serving the people of the state of Florida.

17 responses to “Florida Sea Level

  1. Typo: “just an inch or a few” centimeters

  2. Ed ecce analysis… thought some of those curves–like Fernandina Beach, for one–looked like acceleration was present!

  3. adriancockcroft

    Since much of Florida is porous sea water is penetrating further inland and contaminating ground water. Are there any studies of how fast that is happening? A few mm/year sounds small to people. If it translates to several meters per year of horizontal contamination that may be more relevant. Can the percentage of fresh water aquifers impacted be calculated too?

  4. It’s worth reflecting on a few facts about sea level rise in Earth’s history:

    1: Mean rate of sea level rise during the last deglaciation was 1 metre per century;

    2: Peak rate of sea level rise during the last deglaciation was 4 metres per century;

    3: Today’s global warming is (conservatively) 30 times faster than that of the last deglaciation.

    4: Palaeoclimate data shows pretty reliably that global sea level rise is 20 ± 10 metres per °C of global warming.

    I’d say that’s pretty strong evidence that we’re already committed to tens of metres of sea level rise and at peak rates well in excess of 10cm per decade. The question is how long it takes to really get going, and with the doubling time for Greenland and Antarctic ice melt of (apparently) less than 10 years, I don’t think it’s unduly alarmist to say that it’s likely to be within this century.

    Not good news for Florida, or any other coastal real estate for that matter.

    • arch stanton

      You left out that global sea level change for the last 8,000 years has been in the neighborhood of a meter or two.

      “Not good news for Florida, or any other coastal real estate for that matter”.

      I don’t want to subsidize rich real estate investors. Obviously that is what the whole Florida republican censorship is about.

  5. I don’t deny there is danger in rising sea levels. You provide evidence that the rise rate is accelerating. This certainly bears watching but does not yet reach the level of committing billions of dollars. Referencing the time series of annual data and “looking back” 13 years provides a sea level rise rate between 4 and 5 mm/year. If we transported back in time to 1975 and looked back 13 years the corresponding sea level rise rate would be 9.9 mm/yr. Using your data the most recent 10 year period has a sea level rise rate of 6 mm/yr. The 10 year period ending in 1948 had a sea level rise rate of 12.4 mm/yr. Again this bears watching but it would not have made sense to spend billions in 1948 or 1975 based on this kind of analysis, and it may not now.

    [Response: What’s next? Will you proclaim that the 2-year period from 2009 through 2010 showed a negative rate so there’s nothing to worry about?

    As for “committing billions of dollars,” that is exactly what you are proposing yourself. But the billions you commit aren’t present spending, they’re future damages, and will far exceed the billions you’re talking about. But hey, as long as it’s not your money but somebody else’s livelihood — or life — what do you care?

    It’s quite clear that you aren’t willing to listen to reason. Instead you invent reasons not to believe.]

  6. Thanks Tamino–I was in Florida in March and learned first hand about the unmentionable terms while talking with a Florida water district manager scientist. Then I was shocked to learn that a recent Univ. of Florida Ph.D. needed to edit the terms out of a manuscript for peer review because of the supervisor of her co-author who works for the Florida Dept. of Health. My question is: “How long before building expensive high rise condos on the beach at Miami becomes a money losing proposition?”

  7. Pete Dunkelberg

    Icarus, have some of the past sea level estimates been revised downward? Are you drowning the Windover people? When was the Atlantic ridge along Florida most recently below water, does anyone know?
    We have already raised temps a good bit above pre-industrial. If the sea is going to come up 20 m it had better hurry.

    Still, florida is like the USA in having ocean on three sides and lots of coastal population. If the ocean gets just 1 m higher we are in trouble.

  8. Pete Dunkelberg

    Coastal communities presumably save money by building all new infrastructure to all for sea level rise, say 5 feet since the USGS has that all mapped out for them. The high rise beach front condos on the other hand are a bonanza thanks to the incredible property taxes paid per unit. The people who live there are making their choice and can afford to move if they must during their perhaps already retired life span. The poor will suffer as usual.

  9. John Smith

    why would my comment be in moderation?

    [Response: Because everybody’s comments are moderated.]

  10. Steven Goddard regularly claims no SLR in Florida. One day when I was procrastinating I decided to compile a plot of nearby tide gauges (similar to yours). His response to the observed rise was: “Gravity pulls tide gauges down over time.” https://archive.is/1dbTO

    Now he is into comparing old and new beach photos, -but ignoring that the beaches have to be and are being actively maintained with beach renourishment projects (not cheap). Here’s an example where his new image was taken right after such a project. https://twitter.com/AGrinsted/status/592433104586932227

    • Denis Cartledge

      “Gravity pulls tide gauges down over time”
      Interesting comment that. Recent research coming out of Antarctic studies show that the continental ice melting and flowing into the ocean around Antarctica is also affected by gravity. The greater landmasses in the northern hemisphere will do what gravity does and attract lots of that water, to the northern hemisphere.

      If Florida doesn’t think it can handle its Governor’s progressive intellectual forays, you can always direct him to Australia. Our Prime Minister is on record as saying “Climate Change is crap”. When he won the last election and formed Government, it was the first time since 1931 that Australia’s Commonwealth Government has not had a Science Minister. So your Rick Scott will be in good company. Although lots of Australians believe that intellectual levels of that gathering are marginally just above the primordial slime. Probably just before the Great Oxygen Event ;-)

  11. This video (ht rabbit) is good fun… well very depressing at the same time, but who said they are mutually exclusive

  12. Bernard J.

    But sea level rise is canal food!

    Or something.

  13. Bernard J.

    Tamino.

    The first 15 years or so of the monthly anomaly data seem to be more variable across short periods than the latter part of the dataset. Is there any indication if this is at least in part due to the number/location of the earlier stations, or to the accuracy/precision of the instrumentation?

    [Response: There’s definitely much less data during the earlier time period.]

  14. michael sweet

    Tamino,
    When I reviewed your summary of Foster and Brown you did not give your estimate of acceleration of global sea level rise. Does your analysis suggest global sea level rates have accelerated as much as the above graph suggests Florida’s rate has accelerated? Do you have a link to your analysis on this?