Sea levels along many of the world’s coastlines may be significantly higher than commonly assumed, according to new research published Wednesday in Nature. The study argues that the baseline used to assess future sea level rise and coastal flooding risk is often incomplete, which could cause communities to underestimate how soon impacts arrive.
Rising seas are among the most visible consequences of human-driven warming and pose growing threats to low-lying cities, deltas, and island nations. Scientists estimate that the world is already locked into roughly 6 inches of global sea level rise by 2050. But the new research suggests that many coastal assessments may start from a sea level that is already higher than the models assume.
Models Often Miss Local Drivers of Sea Height
The study focuses on how researchers estimate present-day coastal sea level when projecting future hazards. Many analyses rely on a model framework that infers sea level based on Earth’s gravity field and rotation. While useful for global-scale comparisons, that approach can fail to fully incorporate local and regional influences such as tides, winds, ocean currents, and changes in temperature and salinity.
For more dependable assessments, sea level models should be combined with real-world measurements, including satellite observations that directly track sea surface height, said study author Philip Minderhoud, an associate professor at Wageningen University and Research in the Netherlands.
Review Finds Heavy Reliance on Assumptions
The researchers reviewed 385 peer-reviewed studies published over the past 15 years that examined sea level rise and coastal hazards. They found that about 90% relied primarily on model-based assumptions rather than measured observations. Minderhoud described this as a “methodological blind spot” that can lead to underestimating exposure to flooding and other sea-related risks.
Across global coastlines, the study estimates that coastal sea level is on average about 1 foot higher than commonly assumed. In certain regions, including Southeast Asia and parts of the Pacific, the difference could reach as much as 3 feet.
Implications: Earlier Impacts, Wider Exposure
The authors say higher present-day coastal sea levels do not necessarily change projections for how much sea level rise may occur in coming decades. However, they can shift the timeline for when thresholds are crossed. If the “starting line” is higher than expected for a given coastline, damaging flooding could arrive sooner than many planning scenarios suggest.
The study estimates that if sea level rises by around 3 feet, it could put 37% more land underwater than currently assumed, potentially affecting as many as 132 million people worldwide. The authors argue that these differences matter for coastal zoning, infrastructure design, insurance risk, and decisions about where to prioritize adaptation spending.
Independent researchers quoted in the material described the findings as significant. Matt Palmer of the University of Bristol said the work indicates sea-level impacts have been “systematically underestimated,” while Jonathan Bamber, director of the Bristol Glaciology Centre, said the results were surprising and important for understanding the potential scale of exposure.
Call for Reassessment and Better Baselines
The study authors said additional work is needed to reassess coastal sea level baselines globally and to better quantify what the revised estimates mean for near-term and long-term risk. They also suggest researchers and planners should more consistently combine models with satellite-based observations to avoid undercounting present-day vulnerability.