California has long been preparing for rising sea levels. Communities from Pacifica to Imperial Beach have debated seawalls and relocation efforts. A recent study suggests that our understanding of sea-level rise might be flawed.
Researchers at Wageningen University in the Netherlands published findings in Nature. They analyzed 385 studies on coastal flooding and sea-level rise published between 2009 and 2025. Most of these studies relied on models to estimate ocean heights rather than actual measurements. This means they could be significantly off.
These models, known as geoids, present a theoretical ocean surface, ignoring natural factors like tides and currents. The real ocean is more dynamic. In some areas, this could mean that the sea level is several meters higher than previously thought, putting millions more people at risk of flooding.
The study found that if sea levels rise by about three feet, up to 37% more land may be at risk than previously estimated. This translates to between 77 million and 132 million more people globally who could face flooding.
Globally, coastal sea levels are, on average, about a foot higher than past models suggested, with higher discrepancies in low-income regions like parts of Africa and Southeast Asia. In these areas, data is scarce, leading to reliance on less accurate models. For instance, some parts of Southeast Asia may see differences exceeding three feet.
In California, the discrepancies range from 0.25 to 2 meters. This is alarming for coastal cities already facing challenges. Current assessments show tidal flooding in California has increased by over 550% since 2000. The state is planning for upwards of 10 feet of sea-level rise by 2100.
These outdated assessments put $17.9 billion in buildings at risk with just a 20-inch rise. Additionally, two-thirds of Southern California’s beaches could vanish by the century’s end, according to projections based on flawed data.
Political challenges add to the complexity. Over 30 municipalities in California grapple with how to respond to these threats. Findings from the recent study indicate that coastal planning may not adequately address the scale of the problem.
As climate change continues to evolve, so must our strategies for sea-level rise. California’s preparation needs to adapt to better protect communities against future flooding risks. With the stakes so high, it’s crucial to ensure that assessments reflect reality.
