Coastal sea levels may be higher than previously thought, study says

(NEW YORK) -- Measurements of coastal sea-level height around the world may be higher than scientists previously thought, according to new research.

Past research may even have underestimated coastal sea level heights around the world by an average of .3 meters, or about 1 feet, a study published Wednesday in Nature found.

Sea levels in some areas in the Global South -- regions such as Asia and the South Pacific -- could be up to 3 feet higher than previously assumed, according to the paper.

The United Nations' Intergovernmental Panel on Climate Change estimates that ocean levels may increase by between 0.28 meters and 1 meter by 2100. Human-amplified climate change is the primary cause for present-day rising sea levels, climate research shows.

However, assessments of coastal sea-level often assume overall sea levels rather than the direct measurements of sea-level height in specific regions, according to the paper.

Researchers from Wageningen University & Research in the Netherlands analyzed 385 pieces of peer-reviewed scientific literature on coastal exposure and hazard impact assessments published between 2009 and 2025 and calculated the difference between commonly assumed and actual measured coastal sea level.

They found that 90% of all studies relied on assumed sea levels based on gravitational models -- or geoids -- rather than using the measured sea level, according to the paper.

Earth's gravitational models only account for gravity and Earth rotation and do not account for other factors that determine local sea levels, such as tides, current and winds.

Less than 9% of the existing studies combined land elevation measurements and sea level measurements, but those studies appeared to suffer from conversion errors and data alignment issues, Katharina Seeger a geographer studying flood hazards and risks at Wageningen University & Research in The Netherlands and co-author of the study, said during a press conference Tuesday.

Sea level was found to be underrepresented by .24 to .27 meters, depending on the model used. Some discrepancies were found to be as high as 5.5 meters to 7.6 meters, the researchers said.

The underrepresentations were particularly noteworthy in regions like Southeast Asia, and the South Pacific.

Coastal sea heights were also underrepresented in Latin America, the west coast of North America, the Caribbean, Africa, the Middle East and the Indo-Pacific.

The new estimates could put up to 37% more land below sea level, impacting 77 million to 132 million people globally, the researchers said.

Nearly 40% of the U.S. population lives near the coast, according to the National Oceanic and Atmospheric Administration (NOAA).

Coastal subsidence is often underrepresented in flooding models, a 2024 study published in Nature found. The inundation coastal regions will experience due to rising sea levels may actually be worse than previously thought when factoring in how rapidly the land is sinking, according to the study.

Large cities surrounded by water -- like Boston, New Orleans and San Francisco -- will be among the regions that could experience flooding in the near future due to land elevation changes combined with sea level rise -- about 4 millimeters per year, the 2024 study found.

The sinking is expected to cause structural damage to most existing properties, the authors said.

Parts of low-lying Florida, such as Miami, are already dealing with more frequent and impactful high tide flooding events. High tide flooding, the overflow or excess accumulation of water that covers typically dry coastal land during times of high tide, is happening more often in many coastal communities, even on generally quiet weather days, according to NOAA.

Miami showed the greatest share of exposure to flooding, with up to 122,000 people and up to 81,000 properties that could be at risk of flooding by 2050.

The latest research indicates that re-evaluation of the methodology of existing assessments for characterizing sea-level rise impact is needed, the paper noted. This could have implications for policymakers, climate finance and coastal adaption plans, the scientists said.

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