New Study Indicates Global Coastal Sea Levels Higher Than Previously Estimated

A recent study published in Nature suggests that global coastal sea levels have been underestimated, with current measurements averaging approximately 30 centimeters (one foot) higher than previous calculations. This discrepancy, attributed to methodological differences in measuring sea and land altitudes, indicates potential implications for climate change impact assessments and coastal planning affecting millions of people worldwide.

Global Coastal Sea Levels Higher Than Previously Understood

A new scientific study published in the journal Nature reports that global coastal sea levels are higher than previously understood. The research, which analyzed hundreds of scientific studies and hazard assessments, found that baseline coastal water heights have been underestimated by an average of approximately 30 centimeters (one foot).

The study involved researchers including Dr. Philip Minderhoud of Wageningen University and PhD researcher Katharina Seeger. It reviewed 385 peer-reviewed scientific literature pieces published between 2009 and 2025, combining this analysis with calculations comparing commonly assumed coastal sea levels with actual measured levels.

Methodological Discrepancy Identified

The underestimation is attributed to what the study describes as a "methodological blind spot." A significant majority, over 90%, of the analyzed studies did not utilize local, direct measurements of sea levels. Instead, they relied on land elevation measurements referenced against global geoid models, which estimate global sea levels based on Earth’s gravity and rotation.

This approach often failed to account for real-world factors influencing actual sea levels where the sea meets land, such as waves, ocean currents, seawater temperature, salinity, tides, and phenomena like El Niño.

Many impact studies incorrectly used a "zero-meter" figure as a starting point for sea level, whereas actual measured coastal sea levels can be significantly higher.

Regional Impact and Current Observations

The discrepancy in sea level estimates is more pronounced in specific regions. In parts of Southeast Asia and the Indo-Pacific, actual measured levels were found to be between 100-150 centimeters (up to three feet) higher than prior estimates. In contrast, the underestimation was less prevalent in Europe and along Atlantic coasts.

Coastal communities, such as those in Vanuatu, are reportedly experiencing visible effects including shoreline retreat, erosion, and submerged infrastructure.

Projected Future Consequences

The study's adjusted coastal height baseline suggests that a relative sea level rise of one meter (approximately three feet), a projection made by some studies by the end of the century, could lead to 37% more coastal areas falling below sea level. This revised assessment indicates that between 77 million and 132 million additional individuals could be threatened by inundation.

Higher actual sea levels mean that the impacts of future sea level rise may manifest sooner than previously projected for specific islands or coastal cities.

This presents increased challenges for planning and funding climate change adaptations.

Implications for Climate Policy and Research

Scientists noted that a proportion of the studies identified as potentially inaccurate are referenced in recent reports by the UN Intergovernmental Panel on Climate Change (IPCC). The study provides coastal elevation data integrated with recent sea level measurements and advocates for a re-evaluation of existing coastal hazard study methodologies to inform climate change policy formulation accurately.

The findings, alongside a recent UNESCO report highlighting gaps in understanding the ocean's carbon absorption, suggest that governments may be making coastal and climate risk assessments based on an incomplete picture of oceanic changes.

Expert Commentary

Anders Levermann, a climate scientist at the Potsdam Institute for Climate Impacts Research, stated that the risk of extreme flooding is higher than previously understood, particularly in Southeast Asia. Ben Strauss, CEO of Climate Central, supported the study’s findings, noting that many studies have incorrectly assumed a zero-meter baseline for water elevation.

Conversely, some scientists expressed reservations. Gonéri Le Cozannet from the French geological survey suggested the implications might be exaggerated, noting that the problem is generally understood within the scientific community. Robert Kopp, a sea level expert at Rutgers University, indicated that local planners are often aware of their specific coastal issues.