Evaluating Voortman et al 2025 on Sea Level Rise
The DOE climate assessment report was published a month ago, and already hundreds of scientists have written responses criticizing the handling of the scientific evidence regarding AGW, including 85 scientists who compiled a 400+ page rebuttal and associated press release. In response, the authors of the DOE report appear to be on a PR campaign for damage control, and so Koonin wrote an op/ed for WSJ and Judith Curry took to her blog. Her blogpost attempts to defend her mistakes about sea level rise and acceleration in the DOE report by highlighting a paper that was published this year. The paper claims to show that 95% of tide gauges do not show any statistically significant acceleration, and the remaining 5% have non-climatic explanations for their observed acceleration:
Approximately 95% of the suitable locations show no statistically significant acceleration of the rate of sea level rise. The investigation suggests that local, non-climatic phenomena are a plausible cause of the accelerated sea level rise observed at the remaining 5% of the suitable locations. On average, the rate of rise projected by the IPCC is biased upward with approximately 2 mm per year in comparison with the observed rate.[1]
To evaluate this, it's important to look at what this paper actually does. The study evaluated a subset of two datasets, PSMSL and GLOSS. There are 1548 locations in the PSMSL network, and this study evaluated 204 of them, stating these were the only ones that met the "selection criteria." There are 294 locations in the GLOSS core network, and this study evaluated 39 of them, again stating these were the only ones that met the "selection criteria." There were 28 locations with data both in GLOSS and PSMSL, so this means they used only 215 locations, or less than 15% of the total. Here is their selection criteria:
- "Latest year in the dataset not earlier than 2015...
- Data available over a period of at least 60 years
- At least 80% of the years in the range with data available."
ESA (1991-2019 and ± 82° latitude): 0.095 ± 0.009 mm/yr^2
TPJ (1993-2019 and ± 66° latitude): 0.080 ± 0.008 mm/yr^2
With an acceleration of global sea-level rise during the satellite altimetry era (since 1993) firmly established, it is now appropriate to examine sea-level projections made around the onset of this time period. Here we show that the mid-range projection from the Second Assessment Report of the IPCC (1995/1996) was strikingly close to what transpired over the next 30 years, with the magnitude of sea-level rise underestimated by only ∼1 cm.
The analysis shows that while the overall projection was "strikingly" accurate, the IPCC underestimated the mass loss from ice sheets and overestimated the amount of SLR from thermal expansion: "thermal expansion was overestimated in IPCC-SAR, partly offsetting the low projections for ice-sheet contributions." This kind of analysis from credible scientific journals shows that the overall projections from the IPCC have been on target, but it also provides a helpful correction that could improve projections through the rest of the 21st century.
Curry used Voortman's paper to prop up her rejection of Dessler & Kopp's rebuttal of the SLR section of the DOE report, saying, "Fortuitously, there is a new paper hot off the press: Global Perspective on Local Sea Level Changes.... So yes, some additions to DOE chapter 7 on sea level rise acceleration are warranted, but not in the direction of the Dessler et al. report." At the time of this writing, she has also ignored Törnqvist et al's paper entirely (she said she'd update her post with new info, so maybe she will acknowledge it in the future). It would seem at this point Curry has not done her homework, either in reading Voortman's paper critically or in evaluating the current state of the literature on sea level rise.
References:
[1] Voortman, H. G., & De Vos, R. (2025). A Global Perspective on Local Sea Level Changes. Journal of Marine Science and Engineering, 13(9), 1641. https://doi.org/10.3390/jmse13091641
https://www.sciencedirect.com/science/article/pii/S027311772030034X
[3] Törnqvist, T. E., Conrad, C. P., Dangendorf, S., & Hamlington, B. D. (2025). Evaluating IPCC projections of global sea-level change from the pre-satellite era. Earth's Future, 13, e2025EF006533. https://doi.org/10.1029/2025EF006533
[4] Robert E. Kopp, John Church, Soenke Dangendorf, et al. Faulty science and faulty statistics can't stop sea level acceleration: An expression of concern regarding Voortman, H. G., & De Vos, R. (2025). A Global Perspective on Local Sea Level Changes. Journal of Marine Science and Engineering, 13(9), 1641. ESS Open Archive . September 12, 2025.
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