Subsidence more than doubles sea-level rise today along densely populated coasts

This study addresses the problem of low confidence in estimates of vertical land motion (VLM) and its contribution to relative sea-level (RSL) rise. To tackle this, the authors combine diverse VLM datasets that now cover nearly 65% of the global coastal population, with particular attention to small-scale subsidence in densely populated areas such as East, South, and Southeast Asian cities and deltaic regions that were largely absent from earlier geodetic measurements. By integrating these new data sources, the study aims to produce more reliable estimates of both present and future RSL rise to support coastal risk assessment and adaptation planning at the global scale.

The findings revealed that the average modern (1995–2020) global RSL rise experienced by coastal populations is around 6 mm per year, approximately twice the climate-driven absolute sea-level rise, a discrepancy explained by the strong prevalence of land subsidence in heavily populated coastal zones. Strikingly, 71% of the global coastal population lives in subsiding regions, meaning that human settlement patterns are systematically concentrated in areas where land is sinking. These results underscore that climate-driven ocean expansion alone substantially underestimates the sea-level rise actually experienced by most people, and that integrating VLM observations into risk and adaptation frameworks is essential for accurate projections and effective coastal management policy.