Global Study Finds Coastal Sea Levels Underestimated in Hazard Assessments

A comprehensive review of coastal hazard assessments has identified widespread underestimation of actual sea levels due to reliance on geoid-based models rather than direct measurements.

The meta-analysis, published in Nature, examined 385 peer-reviewed studies conducted between 2009 and 2025. The findings indicate that the majority of these assessments did not use measured sea-level data, which led to lower estimates of coastal sea levels.

Researchers determined that, on average, global coastal sea levels were underestimated by 0.24 to 0.27 meters. In some cases, the discrepancy between estimated and measured sea levels reached as much as 5.5 to 7.6 meters.

The study highlighted that the underestimation was especially pronounced in Southeast Asia, the Pacific, and other areas within the Global South. In certain regions, the difference between model-based and measured sea levels exceeded one meter.

What the numbers show

• 385 publications from 2009–2025 were reviewed in the study
• Over 90% of assessments used geoid models instead of measured levels
• Discrepancies in sea level estimates ranged up to 7.6 meters
• If sea levels rise by 1 meter, up to 37% more land may fall below sea level
• Between 77 million and 132 million more people could be at risk

According to the analysis, if global sea levels increase by one meter, the amount of land projected to fall below sea level could be up to 37% higher than previously estimated. This adjustment could affect between 77 million and 132 million additional people living in vulnerable areas.

The study authors responded by providing open-access datasets that combine coastal elevation with measured sea-level data. These resources are intended to improve the accuracy of future coastal hazard assessments and support more reliable planning.

By making these datasets available, the researchers aim to assist governments, planners, and scientists in updating hazard models and risk assessments. The new data sets are expected to help address previous gaps in coastal risk evaluation, particularly in regions where underestimation was most severe.

The findings underscore the importance of using measured sea-level data in coastal hazard assessments. The study's approach highlights methodological differences that have contributed to discrepancies in global sea-level risk projections.

* This article is based on publicly available information at the time of writing.