Sea Level Rise is Accelerating

Willis gets it right? Not.

Willis Eschenbach has a post at WUWT claiming to show that sea level rise is not accelerating. What he actually demonstrates is that he doesn’t know how to tell.

His method is to fit a straight line to sea level data (from tide gauges) and to fit a quadratic, then compare their “R^2 values.” R^2 is not a test of statistical significance, and neither is the difference from two models. Willis doesn’t know this. He thinks he does — but he’s wrong. I’ll leave it to Willis to figure out why that is (I don’t expect him to be able to do that either).

Evidently Willis also doesn’t know that there are perfectly good, and well-known (for a long time), ways to test the quadratic fit vs. the linear fit statistically. My advice to Willis: crack a book.

Willis uses tide gauge data from PSMSL (Permanent Service for Mean Sea Level), and accepts only data ranging from 1950 through 2015. He then isolates the data since 1950, and further insists that it must be at least 95% complete, i.e., less than 5% of monthly values are missing. He tell us this leaves him with 63 data records, and he is kind enough to provide a link to the data itself. His conclusion, from his analysis, is:

… in every single case the accelerating fit was NOT statistically better than the linear fit.

“NOT ONE of these 63 full tidal datasets shows statistically significant acceleration …”

Let’s take a look, shall we?

Here’s the data from Boston:

The red line is a quadratic fit by least squares. When we test the quadratic term for statistical significance the p-value is 0.0006. That’s statistically significant at the 99.9% level. Of course I corrected for autocorrelation. If I hadn’t — and I suspect Willis doesn’t know how — the estimated p-value would be 2.2 x 10^-11.

Boston isn’t the only example. Willis isn’t just wrong, he’s so wrong, that he reveals he is not qualified to do this kind of analysis. Not even close.

There’s another case worth noting, Juneau, Alaska:

Again, the red line is the quadratic fit. With a p-value of 0.002, it’s significant at 99.8% confidence. But this time, it’s statistically significant deceleration!

Before you declare “Aha — no global warming” be advised that we know why it’s decelerating: because of global warming.

Glaciers are melting so fast that the total mass on land areas is decreasing … the mass of all that water leaves the land and ends up in the ocean. That means the gravity from that ice is no longer pulling the sea closer with its gravity. Because of that, sea levels can actually fall near regions with much land ice melt. So yes, Juneau sea level is decelerating because of global warming.

I wonder whether Willis will dispute that too?

Let’s perform an experiment. Go to the WUWT post and leave a comment referring to this post. Be as polite as you can, stick to facts, don’t get mired in mud-slinging, just point out that Willis is mistaken and link to this post. Let’s find out whether or not your comment appears.

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33 responses to “Sea Level Rise is Accelerating

  1. … and even if there was no acceleration, the sea level would *still* rise …

  2. Robert Wallace

    Is there some way to follow a discussion without commenting?

    I’d like to see how this plays out but I have nothing of value to add to the conversation.

  3. Robert Wallace

    Just noticed that my comment is going to moderation. That’s fine, don’t allow it or this one through. But the comment did allow me to sign up for tracking.

    Seems like it would be less work if you just added a “Follow this thread” widget. Disqus software gives a “Subscribe” option.

  4. Comment entered and ‘awaiting moderation’. We’ll see what happens.

  5. quaesoveritas

    Is the decline in sea level at Juneau not more due to isostatic rebound of the land, rather than the gravitational influence of the ice mass reduction?
    Most of that may be post-glacial rather than the result of recent ice loss.,1

    [Response: Yes the decline is due to isostatic rebound, but the deceleration is due to the gravitational influence of ice mass reduction.]

    • What’s the quantitative reasoning behind the acceleration being due to the reduced gravitational pull of ice on sea water? I’m not doubting that you’ve done the math–I’m curious.
      If the ice-mass loss is ongoing and significant enough to gravitationally affect local seawater levels in a measurable amount, it ought to be significantly affecting rebound simultaneously. And if isostatic rebound is something less than an instantaneous process, successive years of increasing melt could produce an acceleration in rebound.

      • OtherMike, the gravitational effect on the water is transmitted on a mobile liquid, therefore quickly responds, whilst the isostatic rebound requires the magma (which only moves mm a year or on that order) to move in and “fill up” the pressure drop underneath the landmass. That is a lot slower to respond.

        Likely a few other differences, such as the ability of the landmass solid rock to flex, etc, but those two would seem to be the biggest differences from a quick think.

      • Jerry Mitrovica has several YouTube seminar presentations on this. If you want more use Google Scholar.

  6. Is there an explanation for the global sea level being flat for quite a while?? Better on AVISO site as Colorado still display 2016 value.
    Not that I doubt the calculated acceleration. Thank you for the explanation. Simple enough if you have good statistical knowledge.

    [Response: It has recently been announced that an adjustment applied to the earliest satellites depressed their estimates, hiding the acceleration since 1993. When that adjustment is omitted, the satellite record is in better agreement with the tide-gauge record. Of course deniers say the new “adjustment” (actually removal of a previous adjustment) is fraudulent. That’s their go-to response to anything that doesn’t go their way.]

    • Henry – look at the AVISO graph and assess the lengths of time when the rate of SLR is either above or below the trend line. It usually pretty short. The current length of time it has been above the trend line is the longest length of time the rate of SLR has remained above the trend line. I believe it is longer than any of the excursions below the trend line.

      If the rate of SLR remains above the trend line for a very long time, eventually I suspect there is a name for that.

      • Is there an explanation for the global sea level being flat for quite a while?? …

        I think Henry referring to the flat nature of the AVISO graph starting at about September 2015 and still present as of the April 2017 update. I believe it is the slowest regression to the mean in the satellite altimetry era. The cause, I guess, is the very brief and weak La Niña in 2016 simply failed to pull the rate of SLR below the trend, which is usually does.

      • “Is there an explanation for the global sea level being flat for quite a while??”

        Why do people continually think there are clear explainable reasons for the noise in an analysis?

    • Better on AVISO site as Colorado still display 2016 value.

      I emailed them Uni of Colorado in May to ask when the data would be updated. The quick reply was that they are performing a software upgrade, with the advice that the data would be updated “within the next month,” so either the software upgrade hasn’t gone smoothly or other factors are contributing to the delay. Last update was 10 months ago. The previous longest period between updates was 6 months – updates usually take longer from the last of the previous year to the first of the next.

  7. Willis has added a footnote to the article in response.

  8. not sure why NOAA shows a pretty linear trend. What am I missing?

    [Response: NOAA shows the trend estimated by linear regression, so of course it’s linear. They make no attempt (and no pretense) to test for departure from the linear trend.

    Note also that the record at Boston shows both increase and decrease of the rate of sea level rise throughout its history. This seems to be just too complicated for deniers to wrap their heads around.]

  9. russellseitz

    Tamino, it’s not that simple to comment at Watts – he maintains a whitelist as well as a blacklist:

  10. Several comments appear to have made it. The post now has an update, responding to Tamino’s points. Game on?

  11. Planet Watsupia has now appended an UPDATE which is flagged at the top of the post. Given the update seems to be admitting that the method of his post is wrong, hiding this correction UPDATE at the end is not really the done thing.
    Willis tells the Wattsupians “Over at Tamino’s website, … he points out that there is a simpler and more accurate method for finding out if a dataset contains acceleration. … he is correct.
    “My thanks to him for pointing this out, although I do have to deduct points for his repeated ad hominem attacks on me in his post … haters gonna hate, I guess.
    “Using his method I identified seven of the sixty-three stations as having statistically significant acceleration and three stations with statistically significant deceleration.”
    (My bold)
    Willis concludes that he finds the resulting accelerations in SLR are too small to be a worry to man nor beast, telling us “Whatever any future sea level acceleration turns out to be, it is very unlikely to put the Statue of Liberty underwater anytime soon …” That is good to know as the foundation of the statue is 2.7m above sea level (according to Wattsupian measurements). Of course, it is more storm surge and less SLR that will threaten the Statue of Liberty in future years. For instance, Sandy saw a 4.2m surge measured close nearby.

    One point of pedantry to make with the OP here – Is it correct to say that SLR (and note it is certainly not correct for SL) to say a negtive acceleration counts as a deceleration? I say you would not.

  12. So far it appears ignoring the comment seems to be the tactic. Wutters appear trained not to think sceptically.

  13. Susan Anderson

    Can’t bring myself to either contribute clicks or provide my email to sites like WUWT, sorry. So far, that seems safer. But I did show up here because I just thought up an OT doozie about bloggers who promote falsehood.

    Judith Curry is a whole lot like Kellyanne Conway. Think about it! A victim bully by another name would smell as sweet.

  14. Juneaus downward sea level trend is not caused by gravitation changes due to melting ice, but the result of the rising of the land in this part of Alaska. GPS measurements by SONEL give 16.68 mm/year since the start of the measurements end 2005. This means that the spectecular relative sea level fall in Juneau is in fact an absolute sea level rise. See for graphs and links.

    [Response: Yes the downward trend in relative sea level is due to isostatic rebound — but its *acceleration* is due to gravitational changes from melting ice.]

  15. J. Richard Wakefield

    Your Boston graph is cut way too short, why did you do that? Data for it goes back to 1920s, and shows NO acceleration.

    [Response: I’m not the one who selected the time span for the data; that would be Willis Eschenbach (he started all his analyses in 1950). I was checking his results, and used his data file.

    As for “shows NO acceleration,” evidently you are no more competent to reach such a conclusion than he is. As in, not at all.]

    • J. Richard Wakefield

      Sat data shows sea level rise doubled in rate in 1990, 100% acceleration in one year. And not one surface station shows this? Explain.

      [Response: No, it doesn’t.

      You’re just a troll who wants to pick a fight about sea level acceleration. You also seem unaware just how much you embarrass yourself with your comments.

      Stick around. We’ll take a closer look at Boston sea level soon. It would please me greatly to hear your comments on that.]

      • J. Richard Wakefield

        So the sat data isnt 3.4mm/year every year since 1990? That’s what all their graphs show.

        Then tagged to station data like this:

        Looks pretty instant doubling in 1990 to me.

        [Response: Just because someone fits straight lines to data, doesn’t mean the data follows straight lines. You seem to be another one of those who thinks he sees straight lines, then declares them to be a fact.

        Also, it’s curious that you don’t link to the page which states that this graph shows “Sea level change for 1900-1992, based on tide gauge measurements, … , but multiplied by 0.78 to have 1901-1990 trend as 1.2 mm/yr as stated in C.C. Hay, et al.” It’s also quite clear that the rates they quote are averages over long time spans, not instantaneous rates. I guess that’s just too complicated for you.

        Apparently you don’t know that the global estimate based on tide gauges used in that graph (from Church & White) extends beyond 1993. I’ll do another post, so you can see what it looks like when it’s not multiplied by 0.78 and isn’t cut off at 1993 (we know how sensitive you are to not showing all the data). That’s what I call fun!

        And by the way, the satellite data start in 1993, not 1990 (actually, very late 1992 to be more precise). Sloppy scholarship doesn’t help.

        Your insistence that we “explain” that the rate since 1993 is a lot faster than the average rate from 1930 to 1993, is the logical fallacy called “argument from incredulity” — it reminds me of Bill O’Reilly saying “Tide comes in, tide goes out, you can’t explain it.” Neil deGrasse Tyson replied, “I can explain it.”

        By the way, you should definitely read the latest post about sea level at Boston. We welcome your comments.

        Thank you so much for drawing more attention to the acceleration of sea level rise. Keep ’em coming!]

      • Sat data is a straight line, starting in 1990.

      • Sat data is a straight line, starting in 1990.

        This immediately tells us that you only look at graphs and do not read sources.

        “Satellites began to measure sea level precisely in 1993.”

        That information comes from… the source page for the first graph you linked. (The graph is 2 years out of date)

        The same is stated at the source page for the second graph you linked.

        Set your psyche to 100% curiosity to continue more successfully here.

      • J. Richard Wakefield

        ““Satellites began to measure sea level precisely in 1993.””

        And what did they measure sea level rise at in the 1993-1995 period? 3.4mm per year. And 3.4mm per year there after, Hence the rate doubled in 1993.

        [Response: The estimated rate, using satellite data, from 1993 to 1995 (a rather ridiculous choice, but you made it) is 0.4 mm/yr. Not 3.4, 0.4.]