Global sea levels are rising, French landmark doesn't prove otherwise | Fact check
The claim: Water level at Mont Saint-Michel shows sea levels aren't rising
A May 5 Instagram post (direct link, archive link) shows an image of the French landmark Mont Saint-Michel alongside a CNN story about the century-old citadel.
Additional text included in the post reads, "CNN: sea levels are rising," and "Also CNN: heres a 1000 year old citadel that shows sea levels havent ever been rising (sic)."
The post garnered more than 18,000 likes in less than three weeks.
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Our rating: False
The existence or extent of global sea level rise cannot be determined based on just one specific geographic area because relative sea level rates vary worldwide, according to researchers. Steady sea level rise has been recorded on the National Oceanic and Atmospheric Administration tide gauges nearest Mont Saint-Michel.
Global sea levels rising
Mont Saint-Michel is a tidal island off the coast of Normandy, France, renowned for the Medieval abbey built atop it. It became a UNESCO World Heritage site in 1979.
While the post claims that the water level at Mont Saint-Michel's shows sea levels aren't rising, researchers previously told USA TODAY that one isolated geographic area cannot be used to measure average global sea level rise. This is because relative sea level rise rates vary greatly by location.
According to NOAA, sea levels in any given area can be affected by:
Vertical movement of land due to human activity or slow natural processes following the last ice age
Changes in gravitational forces due to the redistribution of mass on Earth as glaciers and ice sheets melt
Differences in wind and ocean current patterns in different areas
Jean-Paul Deroin, a geoscientist at Université de Reims Champagne-Ardenne in France, told USA TODAY that sea level rise is impacting sedimentation processes in the Mont Saint-Michel Bay. The nearest NOAA tide gauge stations, located in Brest, Le Havre and St. Nazaire, France, all show sea level rise.
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The post also mischaracterizes the CNN article it shows, since the article referenced in the post didn't mention sea level rise at all.
Average global sea levels have risen roughly 8-9 inches since 1880, and the rate of sea level rise more than doubled from the 20th century to the early stages of the 21st century, according to NOAA. This rise has been confirmed by measurements from both satellites and tide gauges.
To calculate global average sea level rise, scientists include measurements from all over the Earth.
USA TODAY reached out to the Instagram user who shared the post for comment but did not immediately receive a response.
Our fact-check sources:
Jean-Paul Deroin, May 15, Email exchange with USA TODAY
CNN, June 14, 2023, The 1,000-year-old citadel that rises out of the Atlantic Ocean
UNESCO World Heritage Convention, accessed May 14, Mont-Saint-Michel and its Bay
Permanent Service for Mean Sea Level, accessed May 14, Data Explorer
NOAA, accessed May 14, What is glacial isostatic adjustment?
NOAA, accessed May 14, Global vs. Local sea level
NOAA, April 19, 2022, Climate Change: Global Sea Level
NOAA, Aug. 10, 2017, Tracking sea level rise ... and fall
NOAA Tides and Currents, accessed May 14, Sea level trends
NOAA, Aug. 24, 2023, What is subsidence?
NASA Vital Signs of the Planet, accessed May 14, Ice sheets
Carbon Brief, April 28, 2021, Melting glaciers drove ‘21% of sea level rise’ over past two decades
Normandy Tourism, July 17, 2023, The Mont-St-Michel and its bay
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This article originally appeared on USA TODAY: False claim Mont Saint-Michel disproves sea level rise | Fact check
