The Numbers Were Wrong

For years, coastal flood assessments, climate adaptation plans, and IPCC reports have relied on sea level estimates derived from global geoid models — mathematical representations of Earth's gravity and rotation that provide an approximation of where sea level should be.

The problem, according to a landmark study published this week in Nature, is that those models are significantly wrong. And the error is not small.

Globally, ocean levels are an average of 30 centimeters higher than previously believed. In parts of the global south — including Southeast Asia and the Indo-Pacific — the discrepancy reaches 100 to 150 centimeters.

What Went Wrong

The research, led by Dr. Philip Minderhoud of Wageningen University and PhD researcher Katharina Seeger, analyzed 385 peer-reviewed scientific studies published between 2009 and 2025. They found that more than 90% of these studies did not use local, direct measurements of sea levels. Instead, researchers used land elevation measurements referenced against global geoid models.

The problem is that geoid models provide only a theoretical estimate of sea level based on gravity. In reality, actual sea levels are influenced by winds, ocean currents, seawater temperature, and salinity — factors that vary enormously by region.

The result: a systematic undervaluation of sea levels by an average of 24-27 centimeters depending on the model used, with some individual discrepancies as large as 550-760 centimeters.

Minderhoud calls it an "interdisciplinary blind spot" — a methodological error that has propagated through thousands of studies and into the IPCC's own climate change reports.

The Human Cost

The implications are staggering. Following a relative sea level rise of just 1 meter, the researchers estimate that 37% more coastal areas will fall below sea level than previously projected, affecting up to 132 million additional people.

"If sea level is higher for your particular island or coastal city than was previously assumed, the impacts from sea level rise will happen sooner than projected before," Minderhoud said.

For Southeast Asia, the findings are particularly alarming. The region is home to some of the world's most densely populated coastal areas — Jakarta, Bangkok, Ho Chi Minh City, Manila — cities that are already grappling with flooding and subsidence. If actual sea levels are 100-150 centimeters higher than models suggest, the timeline for catastrophic flooding may be years or even decades ahead of schedule.

What Needs to Change

The study includes ready-to-use coastal elevation data integrated with the latest actual sea level measurements, and the authors are calling for a wholesale re-evaluation of existing coastal hazard studies.

The concern is that a large proportion of the studies they analyzed — studies that form the basis of current climate policy — are fundamentally inaccurate. If the IPCC's projections of 28-100 centimeters of sea level rise by 2100 are being applied to a baseline that is already 30 centimeters too low, the real-world impacts will arrive faster and hit harder than anyone has planned for.

The Bottom Line

This is not a story about climate models being wrong in the abstract. It is about flood walls being built too low, evacuation plans being calibrated to the wrong numbers, and hundreds of millions of people living in zones that are more dangerous than anyone told them.

The sea was always higher than we thought. Now we know by how much.