For decades, California has been bracing for the sea. Communities from Pacifica to Imperial Beach have grappled with seawalls, buyout programs to relocate residents away from vulnerable shorelines, and the politically charged debate surrounding “managed retreat.”
Now, a new study suggests that many of these plans may have been built on a shaky foundation.
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### New Research Challenges Existing Sea-Level Assessments
Published Wednesday in *Nature*, research conducted by Katharina Seeger and Philip Minderhoud at Wageningen University in the Netherlands reveals significant discrepancies in our understanding of current sea levels along coastlines worldwide.
The researchers analyzed 385 peer-reviewed studies on coastal flooding and sea-level rise published between 2009 and 2025. This sample included dozens of reports cited in the United Nations’ most recent major climate assessments.
They found that more than 90% of these studies made a fundamental error when measuring sea level relative to the land: instead of using actual, measured ocean heights, they relied on mathematical models known as geoids.
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### What Are Geoids?
Geoids estimate where the ocean surface *should* sit based on Earth’s gravity and rotation. Essentially, they sketch a modeled ocean absent of tides, currents, winds, and temperature differences.
However, the real ocean does not conform to these assumptions. In some regions, this means the actual sea level could be several meters higher than previously believed, placing millions more people at risk of flooding.
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### Corrected Estimates Reveal Greater Risk
After recalculating sea-level rise using corrected measurements, the researchers found that:
– Under a scenario of roughly 3 feet of sea-level rise, up to 37% more land could fall below sea level than current models predict.
– Between 77 million and 132 million additional people worldwide might be at risk of inundation.
– On average, real coastal sea levels globally are about one foot higher than prior models suggested.
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### Regional Disparities Are Significant
Discrepancies were largest in lower-income regions such as parts of Africa, Southeast Asia, and the Pacific. These areas usually have fewer local tide gauges and rely heavily on geoids that perform poorly there.
For instance, in some parts of Southeast Asia and the Pacific, the difference between modeled and actual sea-level height exceeds 3 feet.
These regions are already among those most vulnerable to rising seas and associated risks.
By contrast, data-rich regions like Western Europe and the eastern United States showed smaller discrepancies, thanks to more robust local ocean monitoring.
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### Implications for California and the U.S. West Coast
The study identifies the West Coast of North America — including California — as a region where sea levels have likely been underestimated.
Discrepancies along the Pacific Coast range from approximately 0.25 to 2 meters (about 10 inches to 6.5 feet).
These findings underscore the urgent need for updated assessments to ensure coastal cities are adequately prepared for the true scale of sea-level rise.
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### The Urgency of Proactive Planning
Tidal flooding has already increased by over 550% in some California coastal cities since 2000. Current state recommendations plan for between 1 and 6.6 feet of sea-level rise by 2100, with some scenarios forecasting as much as 10 feet under the worst emissions conditions.
Existing reports estimate that a rise of just 20 inches could put $17.9 billion worth of buildings at risk statewide and threaten two-thirds of Southern California’s beaches with disappearance by century’s end.
However, these projections rely on the same hazard research called into question by Seeger and Minderhoud’s study. It remains unclear how updated assessments will change these risk estimates.
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### The Politics of Coastal Planning
Los Angeles Times reporter Rosanna Xia has detailed how contentious coastal planning can be, with over 30 municipalities struggling to determine the best approaches.
Now, this new research adds another layer of complexity—one suggesting that many cities and residents may have consistently underestimated the severity of the problem.
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### Looking Ahead
This study highlights how planning for a slow-moving, politically charged issue like sea-level rise is inherently complex and evolving. Unlike sudden disasters such as wildfires or earthquakes, sea-level rise demands long-term, adaptive strategies.
The key question moving forward is whether California’s planners and hazard assessments will catch up to the true scale of the threat posed by rising seas.
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*Stay tuned for updates as researchers and policymakers respond to these new findings.*
https://www.latimes.com/environment/story/2026-03-06/sea-levels-are-already-higher-than-we-thought-according-to-new-calculations
