For years the Intergovernmental Panel on Climate Change (IPCC) has warned of rising sea levels as a result of human-caused climate change, but they have been using model-produced estimates of sea levels, instead of real-world tide-gauge measurements.
This seems at odds with scientific integrity, as historic tide-gauge measurements from around the world are available, and give a long term “real-world” record of trends in sea level rise.
Now, a peer-reviewed study – published in the Journal of Marine Science and Engineering – has used datasets of local sea level information, and found that the IPCC projections of rate of sea level rise is “biased upwards”.
The finding has led investigative journalist and former environmental activist, Michael Shellenberger, to claim that the IPCC scientists misled the public on the measurement and meaning of 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 millimeters per year, or 15 centimeters 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 Shellenberger.
Through a long series of email inquiries and responses with one of the world’s leading sea level rise scientists, Shellenberger says he encountered obfuscating argumentation which refused to address the central question of why scientists would chose modelled measurements instead of using the historic tide-gauge measurements.
Instead, Shellenberger says, appeals were made to authority and the credibility of the published peer-reviewed study – entitled A Global Perspective on Local Sea Level Changes – was attacked. The study looked at global sea level rise using historic tide-gauge measurements.
That study said that the new sea level projections published by the IPCC in 2021 “gave insight into expected relative sea level rise locally” – but noted that a comparison of how local projections compared to local observations had not been made.
Researchers looked at tide-gauge stations with at least 60 years of data in the Permanent Service for Mean Sea Level database, National Review reported. Two hundred of 1,500 stations met the criteria.
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 past 30 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 [tide gauge] 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 such as earthquakes, extensive construction, or post-glacial effects “almost always” explained the local trends.
The researchers subjected the selected databases to a statistical procedure to test for acceleration of sea level rise. “In both datasets, approximately 95% of the suitable locations show no statistically significant acceleration of the rate of sea level rise,” the study found.
“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,” the study concluded.
Shellenberger says that: “for years, the Intergovernmental Panel on Climate Change, or IPCC, has claimed that human-caused climate change has accelerated sea level rise.” But he believes that claim is “false”.
“This does not mean that climate change isn’t happening. It is. It simply means that it has not caused the sea level to rise at a rate any higher than one would expect without human-caused climate change,” he adds.
Shellenberger wrote that the IPCC “introduced modelling that, depending on the assumptions, could show deceleration, linearity, or acceleration. Moreover, given that we have over 150 years of real-world data, they didn’t need to use such complicated modelling.”
Historic tide gauge measurements have been taken around the world for hundreds of years, including in Dublin Bay.
The extensive study referenced above showed evidence that sea levels are rising, and have risen at a steady rate of approximately 1.5mm/year over the past 150 years. They have not shown an accelerating rate of rise in recent decades.
The study has been criticised by Shellenberger’s correspondent, Climate and Sea level scientist, Robert E Kopp, who said in a preprint that the result “stands in contrast both to other studies conducting similar tide-gauge analyses” and “the broader body of knowledge regarding global-mean sea level change and its drivers”.
Scientists will continue to argue the issue, or at least that should be the case since the science should very rarely be considered “settled”. It would seem unreasonable, however, to dismiss the use of real-world measurements if those results don’t suit the narrative established by the current consensus.