A new analysis reveals that most studies on coastal vulnerability have underestimated current sea levels by an average of 24 to 27 centimetres because they overlooked key oceanographic factors. This methodological blind spot means that flooding and erosion risks will materialize sooner than previously projected, potentially affecting millions more people by 2100. Researchers from Wageningen University highlight the need for better integration of sea-level data in climate impact assessments.
Researchers Katharina Seeger and Philip Minderhoud from Wageningen University in the Netherlands examined 385 peer-reviewed studies on coastal vulnerability. They found that 90 per cent of these studies did not account for influences such as ocean currents, tides, temperature, salinity, and winds on sea levels. As a result, coastal water levels were underestimated by 24 to 27 centimetres on average.
This error stems from researchers often using unadjusted geoid models—representations of mean sea level based on Earth's gravity and rotation—without incorporating local variations. Actual sea levels can be several metres higher in areas where winds or currents accumulate water or where thermal expansion occurs. Coastlines also shift due to sediment deposition or groundwater extraction. Less than 1 per cent of the studies accurately determined current coastal sea levels, with many using inconsistent geoid models for land and sea elevations.
Correcting for these oversights could increase the projected number of people facing inundation by 2100 by up to 68 per cent, adding 132 million individuals at risk. The majority of these additional impacts are in South-East Asia and Oceania, where sea levels are on average 1 metre higher than previously estimated, and up to several metres in some spots.
Philip Minderhoud noted at a briefing: “If a representative from a place like that comes to a global gathering and tries to gather support… it can be quite frustrating if there’s this type of scientific assessment that actually says… it will only be affected in the next century, while in reality the area is actually much more exposed.”
Projections of up to 1 metre of sea-level rise by 2100 remain valid, but the baseline was too low, accelerating the timeline for consequences. Forty-six of the reviewed studies informed the latest Intergovernmental Panel on Climate Change reports. Katharina Seeger explained: “The coastal research community [is] really focusing on the coastal land, and therefore may not be aware of these sea-level data sets.”
Matt Palmer from the Met Office in the UK called for closer collaboration between climate scientists and coastal researchers, describing the issue as “lost in translation.” He emphasized that underestimates are particularly severe in lower-income regions like African and Asian river deltas, raising concerns of climate justice due to sparser gravity data there. Joanne Williams from the UK National Oceanography Centre advocated for more tide gauges in these areas, stating: “There are many factors that affect sea level at the coast, some of which are quite localised, so the gold standard remains local, long-term, well-calibrated measurements.”
The findings were published in Nature (DOI: 10.1038/s41586-026-10196-1).
