For years, warnings about accelerating sea levels have dominated headlines, fueling calls for sweeping policy changes and massive investments in green energy. But a new peer-reviewed study challenges that narrative head-on, suggesting the rise is far more gradual than previously claimed.
Published in the Journal of Marine Science and Engineering, the research titled “A Global Perspective on Local Sea Level Changes” by Dutch hydraulic engineer Hessel Voortman and researcher Rob de Vos analyzed data from over 150,000 coastal locations worldwide. Their findings indicate that sea levels are rising at a rate of about 1.5 millimeters per year—translating to roughly six inches over the century—mirroring the pace seen in the previous 100 years. This contradicts projections from complex climate models that have forecasted rises of one to three feet by 2100, often based on limited Antarctic observations and assumptions about ocean responses to warming.
Voortman, who initiated the study after discrepancies arose in his flood-protection work for the Netherlands, expressed surprise at the lack of prior scrutiny.
“It is crazy that it had not been done,” he told journalist Michael Shellenberger. “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.”
He went on to detail the effort: “I had to do a lot of programming and automate data imports and data management. I organized it by using databases so that I really knew what I was doing. It was very structured because I was dealing with 150,000 locations and, on average, 100 years of data. That made one and a half million lines of data. I found myself for days working on things that I felt, ‘This is more computer science than civil engineering.’”
The study’s abstract underscores the implications for coastal planning: “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.” In 95% of suitable locations examined, there was no statistically significant acceleration, pointing to local factors like land subsidence or tectonic activity for the anomalies in the remaining 5%. As Voortman noted to Shellenberger, “The average rate of sea level rise in 2020 is (only) around 1.5 mm/year (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.”
As a licensed coastal pilot, I have used British Admiralty charts from the early 17th century to navigate the confined, shallow waters of The Bahamas for over 50 years. I can assure you that the soundings from 1625 have not varied at all from the soundings of 2025.