Time and Tide Gauges wait for no Voortman

Here we go again. An obscure, methodologically poor, paper published with little to no review makes a convenient point and gets elevated into supposedly ‘blockbusting’ science by the merchants of bullshit, sorry, doubt. Actual 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 that sounds familiar, it’s because it happens a lot. In climate science, one classic example was Soon and Baliunas (2003) which instantly made it’s way to the Senate floor (via Inhofe’s then aide Marc Morano). Other examples abound. So what is this week’s example?

As Dessler et al report laid out convincingly last week, and in multiple posts by Tamino/Grant Foster, the sea level chapter in the DOE climate science ‘critique’ was notably poor. They highlighted 5 specific US tide gauge records, showed only four of them, declared that no acceleration was visible, and concluded that no acceleration was present anywhere. Curiously the 5th record (that wasn’t shown) has a very clear acceleration. They then bungled the referencing of the projections and invented a NOAA projection that did not correspond to anything real. Notably, they did no actual analysis. Actual analyses of the tide gauge record show that acceleration is sea level rise is not only widespread, but it is increasingly clear:

Conveniently, rather than defend the indefensible, one of the authors (Judith Curry) in response latched onto a new paper that apparently agreed with her prior vibes. The new paper is Voortman & de Vos (2025) (VdV25) which was published on Aug 27, and hit the contrary-sphere a few days later heavily boosted by Michael Shellenberger and a few others. This paper claims that acceleration in 243 global tide gauge records is only significant in 4% of them. This, to be clear, is rubbish. But as always in such papers, it takes a little work to figure out what has gone wrong.

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

Apart from the basic lack of context that happens when you ignore the satellite record, the main issues are that the statistical model they use is overly complicated and not properly described, the statistical tests for significance are not applied properly, and the correction for multiple hypothesis testing (which assumes there is no correlation across tide gauge records) is just wrong and all but guarantees their erroneous result.

Curiously, almost all of these errors were also made in an earlier Voortman paper, and were raised by the commenters on that paper at the time (Le Bars et al., 2023)!

How will this all play out in the public discourse? The process of comments, replies, and retractions is relatively slow (multiple months to a year) and even with this preprint quickly available, none of the promoters of VdV25 will deal substantively with any of this (they have not done, and will not do, any analysis themselves). It may well be that VdV25 never gets raised again, having served its purpose as a momentary distraction from the critique of CWG report. Whether or not it gets retracted is not really relevant to that.

We have seen this playbook many times before. Judith Curry and Michael Shellenberger are following in the (late) Pat Michaels’ footsteps who continually championed many new ‘blockbusting’ papers that were always on the verge of undermining the climate consensus, but that (somehow!) never quite did. Once folks lose the ability to check these things for themselves, and start basing claims on vibes, their estrangement from the scientific community hardens and the seriousness with which their opinions are taken decreases.

This little episode thus tells us very little about sea level rise acceleration, but quite 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", Journal of Marine Science and Engineering, vol. 13, pp. 1641, 2025. http://dx.doi.org/10.3390/jmse13091641
2. J. Wang, X. Zhang, J.A. Church, M. King, and X. Chen, "Near‐Term Future Sea‐Level Projections Supported by Extrapolation of Tide‐Gauge Observations", Geophysical Research Letters, vol. 52, 2025. http://dx.doi.org/10.1029/2024GL112940
3. 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 amplitude in the Dutch North Sea", Journal of Coastal and Hydraulic Structures, vol. 5, 2025. http://dx.doi.org/10.59490/jchs.2025.0042