The study is the first to be based on local data taken from coastal sites around the world, rather than on models based on extrapolations.
A new first-of-its-kind study by Dutch researchers finds no evidence of a global acceleration in sea level rise due to climate change.
The peer-reviewed paper, “A Global Perspective on Local Sea Level Changes,” published in the Journal of Marine Science and Engineering last month is the first study to be based on local data taken from coastal sites around the world, rather than on models based on extrapolations.
The study, which was conducted as an analysis of more than 200 tide gauge stations worldwide, cuts against the longstanding belief among climate scientists that climate change is leading to rapidly accelerating sea level rise.
The research, conducted by Dutch researchers Hessel Voortman and Rob de Vos, found that the average rate of sea level rise in 2020 is only around 1.5 mm-per-year, or 15 cm-per-century.
“This is significantly lower than the 3 to 4 mm/year often reported by climate scientists in scientific literature and the media,” Voortman told independent journalist Michael Shellenberger.
Voortman told Shellenberger he could not believe that no researcher who had come before him had performed an analysis of real-world local data.
“It is crazy that it had not been done,” said Voortman. “I started doing this research in 2021 by doing the literature review. ‘Who has done the comparison of the projections with the observations?’ And there were none.”
The study was also unlike previous studies of its kind in that it was conducted without external funding; Voortman does not belong to a university, instead he is a hydraulic engineer of 30 years who is involved in flood protection and coastal infrastructure adaptation projects all over the world.
“From practice, I had already encountered the situation that sea level projections were exceeding sea level observations,” he said.
In fact, in 2023, Voortman published a paper that demonstrated that sea level rise along the Dutch coast had not accelerated.
A press release says Voortman was “intrigued” by the findings of his 2023 analysis and decided to repeat his analysis globally, “accounting for known periodic fluctuations in sea levels due to interactions between the moon and earth.”
In order to account for those fluctuations, he looked at tide gauge stations with at least 60 years of data in the Permanent Service for Mean Sea Level database. Two hundred of 1,500 stations met the criteria.
Voortman then applied a statistical test to determine whether a quadratic curve or a straight line better described the measurements from each station.
“For the vast majority of the stations, the differences between the two curves were not significant,” or in other words, an acceleration was not detectable.
A number of studies and scientific bodies have measured sea level rise beginning in 1993, since that’s when satellite imaging became available, and found that there has been a dramatic acceleration in sea level rise over the last thirty years. But Voortman explains that, once periodic fluctuations are taken into account, the effect dissipates. Sea levels were in a “trough” in 1993 and a “peak” in 2020.
“A trend calculated between 1993 and 2020 thus automatically yields higher sea level rise rates, but these are expected to diminish in the coming years, as has happened before,” explains a press release. “Voortman cautions that it is too early to attribute this temporary ‘acceleration’ to global climate change.”
While a “small percentage” of the 200 stations showed “notable, sometimes statistically significant, increases or decreases in sea level,” Voortman found those stations were typically located near others that showed no acceleration, “making it unlikely that a global phenomenon like CO2-driven global warming is the cause.”
Instead, the study found that local factors like earthquakes, extensive construction, or post-glacial effects “almost always” explained the local trends.
Meanwhile, the paper finds the U.N. climate panel IPCC models, which are relied upon by scientists the world over, “significantly overestimate local sea level rise in 2020.”
In its latest report from 2021, the panel says sea levels have been rising at an accelerating rate since 1900. The report published sea level projections for various locations worldwide, while earlier reports only provided global estimates.
But Voortman found the simulated sea level rise in the IPCC’s climate models for 2020 were “systematically too high, on average about 2 mm/year higher than the measured values, with significant regional variations.”
As such, Voortman warns colleagues to use the IPCC projections cautiously.
“When designing coastal infrastructure, engineers have long accounted for sea level rise. Both measurements and projections are important sources of information. Understanding the differences between them is crucial for practical applications,” he said.
Overall, Voortman’s research offers a refutation of years of fearmongering headlines about sea level rise.
Still, despite the groundbreaking findings of his research, Voortman “does not deny the reality of climate change, sea level rise, or the need for models,” according to Shellenberger’s report.
“It is important to stress that there are good reasons to have models. If we as engineers design something in the coastal zone, then we try to achieve a technical lifetime of 50 to 100 years, and that means we need to try to look into the future,” the engineer said.