地球科学：沿岸の海面はこれまで考えられていたよりも高いかもしれない

Most research may have underestimated coastal sea-level height across the world by an average of 0.3 m, according to a study published in Nature. In some areas in the Global South, these levels may be up to 1 m higher than previously assumed. The findings highlight the need to re-evaluate existing values and ensure that future coastal hazard assessments correctly combine sea-level measurements with coastal elevation for a better understanding of how climate change is impacting coastal areas.

Sea-level rise is a major threat to coastal communities, and the Intergovernmental Panel on Climate Change estimates that ocean levels may increase by between 0.28 and 1 m by 2100. However, impact assessments of coastal sea-level rise across the globe often assume sea-level rather than considering local, direct measurements of sea-level height.

Katharina Seeger and Philip Minderhoud analysed 385 pieces of peer-reviewed scientific literature on coastal exposure and hazard impact assessments, published between 2009 and 2025, and performed worldwide meta-analyses to calculate the difference between commonly assumed and actual measured coastal sea level. They found that more than 90% of all studies relied on assumed sea levels based on gravitational models, so-called geoids, rather than using measured sea level. As a result, sea level was underrepresented by 0.24 to 0.27 m depending on the geoid model used, with some discrepancies being as high as 5.5 to 7.6 m. Thus, sea-level rise and other coastal hazard impact assessments were calculated using a coastal sea level that is, on average, lower than the true actual sea level, consequently underestimating coastal exposure. These underestimations were particularly noteworthy in the Global South — specifically in Southeast Asia and the Pacific Region. Underestimates were also observed in Latin America, the west coast of North America, the Caribbean, Africa, the Middle East, and the Indo-Pacific. They note that these issues are the result of the assumption that Earth gravitational models provide an acceptable estimate of local sea-level around the world. However, these models only account for gravity and Earth rotation and do not account for other factors that determine local sea level, such as tides, current, and winds. Through meta-analyses of the most common assumptions found in the published literature and by properly combining coastal elevation to measured sea-level height data, the authors found that compared with previous estimates a hypothetical 1 m of sea-level rise could put up to 37% more land below sea level, impacting 77–132 million people across the globe.

The authors conclude that re-evaluation of the methodology of existing assessments for characterizing sea-level rise impact is needed, with possible implications for policymakers, climate finance and coastal adaptation plans.

• Article
• Open access
• Published: 04 March 2026

Seeger, K., Minderhoud, P.S.J. Sea level much higher than assumed in most coastal hazard assessments. Nature (2026). https://doi.org/10.1038/s41586-026-10196-1