New study in Nature: sea level worldwide higher than previously assumed

The researchers analysed 385 scientific publications and found that in more than 90% of the studies, information on land elevation is not combined with sea level measurements. As a result, many studies – both global and local – underestimate vulnerability to sea level rise.

Meta‑analysis exposes major gaps between measured and theoretical sea levels

Philip Minderhoud, an expert on land subsidence and relative sea level rise at Deltares and WUR, conducted the research in recent years with Katharina Seeger (WUR). The meta-analysis shows that locally measured sea levels worldwide are on average 20 to 30 centimetres higher than the baseline levels, so called geoid models, generally used. In the global South, particularly Southeast Asia and the Pacific, that difference can even exceed 1 metre in some locations.

It has taken years to put all the pieces of the puzzle together because this research involves multiple disciplines, and brings together different datasets and measurement methods.

Philip Minderhoud, Land subsidence and hydrogeology expert

Mismatch between the geoid and the actual sea level

The researchers found that more than 90% of the studies reviewed did not use sea level measurements. Instead, the sea level was estimated on the basis of global geoidal models. Those models provide a theoretical reference based on gravity and the earth’s rotation but they do not take into account local factors such as currents, winds and tides. That almost automatically results in discrepancies between the actual measured local sea level and the level estimated using geoidal models. The largest discrepancies between measured and modelled sea levels are found in the Indo-Pacific region.

Implications for coastal hazard exposure and impact assessments

Because the theoretical sea level (based on the geoid) differs from the measured mean sea level, a relative sea‑level rise of 1 metre would result in 31–37% more land and 48–68% more people falling below sea level worldwide than many studies currently report. This could amount to tens of millions of additional people at risk, particularly in low‑lying deltas, coastal plains and island regions in the Global South. Whether these areas will actually be inundated depends, among other factors, on the level of coastal protection in place — an aspect that falls outside the scope of this study. This underestimate is usually not found in Western countries, including the Netherlands, that have access to high-quality local data such as detailed elevation models and their own sea level measurements.

Reliable data integration and transparency as the new standard

This finding emphasises the need for reliable data integration, transparent documentation and reproducible analysis methods. To support researchers and government authorities, the researchers used supercomputers to integrate four of the latest global digital elevation models with the latest available coastal sea levels. The resulting datasets are available in open access via the paper, allowing countries and organisations to make more accurate coastal analyses immediately.

We hope this will save many researchers complicated calculations and enable more realistic analyses, both globally and locally

Philip Minderhoud

The researchers hope the correct integration of land and sea measurements to become the new standard. This should lead to more reliable hazard assessments so that coastal communities worldwide can prepare more effectively for future sea level rise and other coastal threats.

The paper 'Sea level much higher than assumed in most coastal hazard assessments' is open and freely accessible via: https://doi.org/10.1038/s41586-026-10196-1

Authors:
Dr. Philip Minderhoud, Wageningen University & Research, University of Padova, and Deltares, Associate Professor of coastal-deltaic land subsidence and relative sea-level rise.

Katharina Seeger, Wageningen University & Research, University of Cologne, and University of Padova, post-doctoral researcher on coastal elevation and relative sea-level rise impacts.