Time and tide meters don’t wait for Voortman

Here we go again. An obscure and methodologically flawed paper, published with little or no review, makes a convenient argument and is elevated to supposedly “blockbuster” science by science merchants. shitsorry, doubt. Real scientists drop everything to respond, but not before the (convenient) nonsense has spread widely. Rebuttals are written and submitted, but by the time they are published, everyone has moved on.

If this sounds familiar, it’s because it happens a lot. In climate science, a classic example was Pronto and Baliunas (2003) which instantly reached the Senate floor (through Inhofe’s then assistant, Marc Morano). Other examples abound. So what’s this week’s example?

As Dessler et al convincingly argued last week, and in multiple publications By Tamino/Grant Foster, the sea level chapter in the DOE’s ‘critique’ of climate science was notably poor. They highlighted five specific US tide gauge records, showed only four of them, stated that no acceleration was visible, and concluded that no acceleration was present anywhere. Curiously, the fifth record (which was not shown) has a very clear acceleration. Then they messed up the projection references and invented a NOAA projection that didn’t correspond to anything real. In particular, they didn’t do any real analysis. Actual analyzes of the tide gauge record show that the acceleration of sea level rise is not only widespread, but increasingly clear:

Conveniently, instead of defending the indefensible, one of the authors (Judith Curry) latched onto a new article that apparently matched her previous vibes. The new document is Voortman and de Vos (2025) (VdV25), which was published on August 27 and reached the opposite sphere a few days later, strongly promoted by Michael Shellenberger and some others. This article states that the acceleration in 243 global tide gauge records is only significant in 4% of them. This, to be clear, is garbage. But, as always with these types of articles, it takes a little work to figure out what went wrong.

Fortunately, a group of scientists led by Bob Kopp have quickly put together a rebuttal and retraction request (which has been sent to the journal): Kopp et al. (2025). In it they point out that, in fact, this analysis has already been carried out correctly (Wang et al., 2025published before VdV25 was shipped), and then goes on to explain the basic errors.

Aside from the basic lack of context that occurs when the satellite record is ignored, the main problems are that the statistical model they use is overly complicated and not adequately described, the statistical tests of significance are not applied correctly, and the correction for multiple hypothesis testing (which assumes no correlation between tide gauge records) is simply incorrect and almost guarantees their wrong result.

Interestingly, almost all of these errors were also made in a previous Voortman article and were raised by commenters on that article at the time. (Le Bars et al., 2023)! [Update: They were also noted in a blog post by Scott Simmons].

How will all this be reflected in public discourse? The process of comments, responses and retractions is relatively slow (several months to a year) and even with this preprint available quickly, none of the VdV25 promoters will substantially address any of this (they have not and will not do any analysis themselves). VdV25 may very well never arise again, as it served its purpose of momentarily distracting criticism of the CWG report. Whether he retracts it or not is not really relevant to the matter.

We have seen this manual many times before. Judith Curry and Michael Shellenberger are following in the footsteps of the (late) Pat Michaels, who continually championed many new “blockbuster” papers that always came close to undermining the climate consensus, but (somehow!) never did. Once people lose the ability to verify these things for themselves and start basing their claims on vibrations, their distancing from the scientific community hardens and the seriousness with which their opinions are taken decreases.

Therefore, this small episode tells us very little about the acceleration of sea level rise, but a lot about the seriousness of the people involved.

References

1. H.G. Voortman and R. De Vos, “A global perspective on local sea level changes,” Marine Science and Engineering Magazinevol. 13, pp. 1641, 2025. http://dx.doi.org/10.3390/jmse13091641

2. RE Kopp, J. Church, S. Dangendorf, B. Fox-Kemper, I. Haigh, DL Bars, GL Cozannet, R. Nicholls, M. Oppenheimer, C. Piecuch, R. Riva, A. Slangen, V. Srikrishnan, P. Thompson, RSJ Tol and RVD Wal, “Faulty science and statistics cannot stop sea level acceleration: An expression of concern regarding Voortman, H.G. and De Vos, R. (2025). A global perspective on local sea level changes. Journal of Marine Science and Engineering, 13 (9), 1641.”, 2025. http://dx.doi.org/10.22541/essoar.175766862.22299902/v1

3. J. Wang, X. Zhang, JA Church, M. King, and Geophysical research lettersvol. 52, 2025. http://dx.doi.org/10.1029/2024GL112940

4. D. Le Bars, C. de Valk, I. Keizer, A. Jüling, R. Van de Wal, S. Drijfhout and E. Lambert, “DISCUSSION ON: Robust validation of trends and cycles in sea level and tidal range in the Dutch North Sea”, Magazine of coastal and hydraulic structuresvol. 5, 2025. http://dx.doi.org/10.59490/jchs.2025.0042