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New research reveals that a significant majority of scientific studies have underestimated current sea levels.
The study, published Wednesday in the journal Nature, suggests that ocean levels are an average of 30 centimeters (approximately one foot) higher than previously believed.
The discrepancy stems from a "methodological blind spot" in how scientists measure the intersection of land and sea.
Researchers Dr. Philip Minderhoud of Wageningen University and Katharina Seeger of the University of Padua found that most studies used land elevation measurements referenced against global "geoid" models.
These models estimate sea level based on Earth’s gravity and rotation, but often ignore local factors.
"In reality, sea level is influenced by additional factors such as winds, ocean currents, seawater temperature, and salinity," Minderhoud told The Guardian.
The research team analyzed 385 peer-reviewed studies published between 2009 and 2025.
They discovered that more than 90% of these papers failed to use local, direct measurements of sea levels. Instead, they relied on a "zero-meter" starting point that does not reflect the actual height of the water at the shoreline.
The impact of this correction is most severe in the Global South, particularly in Southeast Asia and the Indo-Pacific. In these regions, actual sea levels are between 100 and 150 centimeters higher than many models indicate.
The study highlights the immediate risks for several nations:
"These studies aren't just words on a paper," said Vepaiamele Trief, a 17-year-old climate activist from Vanuatu. "They're people's actual livelihoods."
Because many scientists started from the wrong baseline, the projected impacts of future global heating will likely arrive sooner than expected.
If sea levels rise by an additional meter by 2100, as the IPCC suggests, the adjusted calculations show that 37% more coastal land will fall below water.
This shift means an additional 77 million to 132 million people worldwide are at risk of losing their homes or facing extreme flooding.
While some experts, such as Robert Kopp of Rutgers University, argue that local planners often understand their specific flood risks regardless of global models, the study authors emphasize the need for better data integration. They described the current situation as "comparing apples to oranges" because satellite land data and ocean data are rarely combined correctly.
The researchers have released ready-to-use coastal elevation data that integrates the latest sea level measurements. They are calling for a complete re-evaluation of existing coastal hazard studies to ensure that government climate policies are based on reality rather than gravity-based estimates.
"If the 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 warned.
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