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A new study suggests that the scientific community has been broadly misrepresenting sea level rise, especially in coastal areas of the global south, due to inaccurate geoid models.

An analysis of 385 sea level measurements conducted during coastal science experiments showed that 99 percent either relied on these geoid models, combined data sets incorrectly, or simply didn’t say how they gauged sea level.

The authors suggest retiring geoid models from coastal science moving forward and present a supercomputer-derived dataset that more accurately represents sea levels worldwide.

Science is only as good as the foundation of data it’s built upon, and a new study from researchers at Wageningen University in the Netherlands suggests that estimates of future sea level rise may have been worryingly underestimated.

This isn't the first time that a scientific misunderstanding has led to a mismatch between sea level data and reality. Inaccurate assumptions about glacial melting rates produced a significant underestimate of sea levels that had to be corrected a decade ago. But the new data snafu stems instead from an inconsistency between how we measure sea levels in science research broadly. Geoids are handy mathematical models that calculate global mean sea level based on gravity and Earth’s rotation. Because Earth isn’t a perfect sphere, these models help scientists accurately calculate sea level when conducting science along coastal areas—or at least, that’s what we thought.

A new study published in the journal Nature took a closer look at that assumption by analyzing hundreds of scientific research publications that used geoid models while conducting research along coastlines around the world. One of the big limitations of geoid models is that they assume a calm ocean, which effectively underrepresents important dynamics like winds, tides, and currents. In Northern Europe and the United States—where seas are generally calmer and scientists have more data sources for sea level rise—these discrepancies are minuscule, but in other parts of the world like Southeast Asia and the Indo-Pacific, the gap between assumed sea levels and real sea levels is cause for concern.

“Researchers who study land elevation or sea levels try to make their elevation models as accurate as possible,” Wageningen University’s Philip Minderhoud, who co-authored the study with his colleague Katharina Seeger, said in a press statement. “Most researchers […] seem to be unaware that it is necessary to use and correctly align measurements of both land and the sea when performing coastal impact assessments.”

Minderhoud first became suspicious of geoid model accuracy while conducting research in Vietnam’s Mekong Delta in 2015, after discovering that the delta (one of the largest in the world) was surprisingly lower than geoid models suggest. He published these findings in the journal Nature Communications in 2019, writing at the time that “our results imply major uncertainties in sea-level rise impact assessments for the Mekong delta and deltas worldwide, with errors potentially larger than a century of sea-level rise.” That instinct proved correct, as Seeger similarly found inaccuracies while conducting her Ph.D. research along the Ayeyarwady Delta in Myanmar.

After poring over hundreds of studies for two years, the researchers concluded that 99 percent of the research they examined either neglected to use sea level measurements (relying on geoid models instead), combined data sets incorrectly, or simply didn’t explain the methods behind the sea-level numbers. While such systematic mismeasurement has potentially disastrous implications for these watery delta regions, the study also found that the reverse can be true—sea levels in Antarctica, for example, are lower than scientists assumed.

Minderhoud and Seeger say that geoid models should be retired from use in coastal research, and they even present an alternative. Using supercomputers, the researchers combined four elevation models with the most recent sea-level measurements, allowing scientists access to highly accurate sea-level measurements in the here-and-now.

“That is how science works,’ Minderhoud said in a press statement. “Now that we have discovered this blind spot, the scientific community can make more accurate assessments for coastal areas and cities around the world.”

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