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Sea Level Rise Lower Than Thought!

May 12, 2015

By Paul Homewood 




Bishop Hill mentions this new paper, also trailed by the Guardian with the headline “Sea level rise accelerated over the past two decades, research finds “. Apparently the new findings now tally more closely with the IPCC models, which must give us all great reassurance!

Here is the paper.



The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability1, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1 (refs 2, 3). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift4, 5). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs 6, 7), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions2, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. 8) and reprocessed ERS-2/Envisat altimetry9. Second, in contrast to the previously reported slowing in the rate during the past two decades1, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections2, 10, and larger than the twentieth-century acceleration2 


It must be noted that, as yet, the University of Colorado and the other recognised providers of the official sea level data have not accepted their “mistakes”, nor altered their data. Till that happens, we should naturally take the Watson findings with a large dose of salt.

Nevertheless, a few pertinent observations are in order:



1) If the rate of sea level rise in the last decade is higher than the previous decade, then so what? Observations of tide gauge data during the 20thC shows periods of faster and slower rise. Such changes are perfectly natural.

2) Sea level rise was slowed down in the mid 1990’s, following Pinatubo, so a speed up again afterwards would be expected.

3) As even the warmist Richard Alley admits “Considering how hard these measurements are, it is not surprising that a new study such as this one finds an additional small correction.Unfortunately, the study doesn’t tell us what we really need to know – how rapidly the sea level will rise over the next century. The satellite record is so short that the observed acceleration is not statistically significant and does not allow us to compare it with existing projections.”


Above all though, what the study has found is that sea level rise in the last 20 years has actually been much less than the official data is showing.

According to Watson, we are looking at between 2.6 and 2.9mm/year, instead of 3.2mm.

We should also remember that both numbers include the fraudulent Glacial Isostatic Adjustment, or GIA. Since the end of the ice age, ocean basins have gradually been getting larger (as ocean bottoms are sinking). Thus, a greater volume of sea can be contained without any increase in sea level. (For more on this, see here).

The GIA tries to reflect this fact, essentially by estimating what sea level rise would be, if the ocean bottoms were not sinking. So far, so good.

The trouble is that the old tidal gauge measurements did not allow for GIA, as they simply measured what was happening at the surface. That is why it is utterly dishonest to splice the tide gauge and satellite trends together,and claim that sea level rise is accelerating.

This GIA is 0.3mm/year.

Taking the GIA out of the Watson figures, we get 2.3 to 2.6mm/year, barely greater than the 20thC rate of rise, variously estimated to be between 1.2 and 2.4mm/year.


Perhaps the Guardian headline should have read:-


Sea level rise lower than thought over the past two decades, research finds

  1. Bloke down the pub permalink
    May 12, 2015 5:32 pm

    With GPS confirmation of sea level gauge movement, there should be no need for the GIA guesstimates.

    • May 12, 2015 6:20 pm

      There’s two different GIA’s !!

      The local one is where land is rising/falling, which as you can say can be checked via GPS.

      However the fraudulent one is all about the ocean bottom falling, relative to the centre of the earth. In theory, this is happening, but it has nothing to do with sea levels, only the volume of the sea.

  2. TonyM permalink
    May 12, 2015 6:28 pm

    It is mind boggling to believe that measurement of sea levels that cover 70% of the Earth’s surface, can be miles deep, and are in constant turmoil, can be measured with millimeter accuracy. They are subject not only to sinking ocean bottoms, but to melting and growing glaciers, the ongoing motions of the tectonic plates, the temperature of the water, the amount of wind, and who know what other forces, . Sea level rise measurements seem to have the same believability as average global temperature calculations. The forces and variables that determine them are so many, so chaotic, and so poorly understood, that these calculations are nothing more than excercises in writing computer programs.

    • May 12, 2015 11:53 pm


      And keep in mind the changes over short periods (yearly. really?) is a small, small number. Easily overwhelmed by uncertainty. Another way to express it is that not much is happening, it isn’t out of the ordinary, and it isn’t much – as a matter of fact, it (AGW, sea-level rise, fill-in-the-blank) is so minute it is practically impossible to measure.

  3. May 12, 2015 7:33 pm

    Wrote about this extensively in essay PseudoPrecision. Reprocessing the satellite altimetry records is suspect. The pseudochange is tiny compared to the error of estimate. Owing to waves, atmospheric humidity (which affects the return signal) and orbital imprecision, the design spec for the newest bird–Jason 2– is accuracy (RMS 1sigma) of +/- 3.4cm (yes, 34mm) with random instrument drift not more than 1mm/year. Previous birds were worse.
    And, differential GPS only gets within a few mm, and has not been around long enough to get a good fix on tide land movements. Another nonscience (pun intended) conclusion manufactured to fit the narrative.

    • Billy Liar permalink
      May 12, 2015 11:44 pm

      How did these genii deal with the inverse barometer correction which must be contemporaneous with the satellite measurement? 1mb (= 1 hPa) error = 10mm error in sea level measurement. I simply can’t see that the satellites can measure the surface barometric pressure at the time they fly over to better than 0.1mb (or hPa). How do the satellites account for the wind moving the water around between satellite passes over adjacent tracks?

    • Billy Liar permalink
      May 12, 2015 11:49 pm

      By the way, I’m sure you know that 3.4cm RMS is the same as 96.2mm peak to peak error – not far off 4 inches.

  4. sunsettommy permalink
    May 13, 2015 1:12 am

    A reader over at JoNova stated: “Reader Robbo wrote in to say he so was astonished at the ABC story, he read the paper, only to find a very different picture and problems he would fail a first year student for:

    Then I carefully read the original paper, and they are completely different from the press release and the ABC version. The paper claims that the rise rate in the last 20 years is actually less than previously thought (that is not mentioned or is at best, carefully massaged by the authors’ press release and ABC piece). But it is true that the title and punchline of the Nature paper is about acceleration: sea level rise is accelerating, they say. And how much is it accelerating? Wait for it: it’s accelerating at 0.043 +/- 0.058 mm/yr2. That’s consistent with zero! I would fail a first year student claiming that 0.043 +/- 0.058 is a Nature-level result.

    Finally, how do they get that acceleration result? They fit a second-order polynomial to the data (Fig 3) and take the coefficient of the t^2 term. Again, basic undergrad science, if the linear fit to the data is statistically acceptable, you take the linear fit (the lowest order polynomial that is statistically acceptable). You can always fit the same data with higher and higher order polynomials and get terms in t^2, t^3, t^4,….and of course when you extrapolate those terms to the future your fit goes wild but that is complete rubbish. In their case, all they should have said was that the linear fit is statistically equivalent to the quadratic fit (because a = consistent with 0), therefore we detect no acceleration, end of the paper.”

  5. Neil permalink
    May 13, 2015 10:25 am

    Why does the University of Colorado interest itself in sea level movement?
    It’s about as far from the sea as is possible in the Continental US, and Dallas is the Mile High City.

  6. Filbert Cobb permalink
    May 13, 2015 11:08 am

    I’m a bit thick when it comes to sea level rise and all that there. If the sea rises, other things being equal – which they often aren’t – shouldn’t that reduce the fall on any river and make it run slower and get wider if the catchment recharge stays the same? Will the tides run further inland? If so is there any evidence that this is so – if people’s feet are getting wet on the way to work of a morning I’d say that was a more reliable indicator than some new-fangled satellite thing.

  7. sarastro92 permalink
    May 13, 2015 2:03 pm

    There have been several of these papers out in the past year. The problem for the catastrophists and climate hysterics was summarized by Cazenave and her team:

    ” Since the early 1990s, sea level rose at a mean rate of ~3.1 mm yr−1. However, over the last decade a slowdown of this rate, of about 30%, has been recorded4. It coincides with a plateau in Earth’s mean surface temperature evolution, known as the recent pause in warming”.

    So these new papers are all devoted to messaging the data in any way possible to reverse the trend (echoing “hide the decline” tactics from the Mann-world temperature proxy data) …

    Obviously issues raised in these papers have to be addressed one by one…. but wholesale reversal of trends in the opposite direction of observed data send up lots or red flag.

  8. May 13, 2015 3:30 pm

    the author misreads the study:
    “accelerating at a rate of between 0.041 and 0.058 mm per year”.

    and gets dimensions wrong

  9. May 13, 2015 10:22 pm

    Thanks, Paul.
    “between 2.6 and 2.9mm/year, instead of 3.2mm”, OK, but taken with a grain of ocean salt. is showing 3.3mm/year in their 2015 Rel. 2 (2015-05-04), they showed 3.2mm/year in 2015 Rel. 1 (2015-02-24).

  10. May 14, 2015 1:39 am

    Thanks again, Paul.
    Now I’m quoting you in my climate pages:
    Scientists may find it useful to include an estimate for GIA, when they do their own analysis. But the official, published number should not include this adjustment, as it is grossly misleading.
    From Some Background To Sea Level Measurements (Paul Homewod, October 16, 2014), at
    The Spanish version:
    Los científicos pueden encontrar útil incluir una estimación de la GIA, cuando hacen su propio análisis. Pero el número oficial publicado no debe incluir este ajuste, porque es muy engañoso.

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