Scientists find sea levels are already much higher than we thought. That could spell trouble for the future

By Laura Paddison, CNN

(CNN) — Sea levels along the world’s coastlines are much higher than previously assumed, more than 3 feet in some regions, according to new research, raising alarms that the world is underestimating the extent of the threat and how quickly coastlines could disappear.

Sea level rise is one of the most visible and alarming impacts of the human-driven climate crisis, threatening hundreds of millions of people who live along global coastlines. Scientists estimate we’re already locked into around 6 inches of global sea level rise by 2050.

But their calculations may not be starting from an accurate place, according to the study, published Wednesday in Nature.

To predict how sea level rise will affect coastal communities, scientists often use a model which estimates sea level by looking at the Earth’s gravitational field and rotation. But this doesn’t account for other influencing factors, such as tides, winds, ocean currents, temperature and saltiness.

For reliable sea level information, the model should be combined with real-world satellite data that can accurately measure sea height, said Philip Minderhoud, a study author and an associate professor at Wageningen University and Research in the Netherlands.

The report authors analyzed 385 peer-reviewed studies published over the past 15 years on sea level rise and the hazards it poses to coastlines. They found 90% relied only on assumptions from models rather than real, measured observations.

It’s a “methodological blind spot” that has resulted in widespread underestimations of coastal sea levels and people’s exposure to their related hazards, Minderhoud said.

Global coastal sea level is on average around 1 foot higher than currently assumed, the report found, with some places — such as Southeast Asia and parts of the Pacific — reaching up to 3 feet higher.

The findings suggest that if sea level rises by around 3 feet, it would put 37% more land under water than currently assumed, affecting up to 132 million people across the world.

“Simply put, if sea level in reality is higher for your particular island or coastal city than was previously assumed, the impacts from sea-level rise will happen sooner than projected,” Minderhoud said.

The findings show “the impacts of sea-level rise under climate change have been systematically underestimated,” said Matt Palmer, an associate professor at the University of Bristol, who was not involved in the study.

Jonathan Bamber, director of the Bristol Glaciology Centre, who has worked on sea level rise for around 20 years, said the results left him “genuinely surprised.”

Wrong assumptions about present-day sea level rise will have important implications for the future “in terms of the area and number of people potentially affected,” said Bamber, who was also not involved in the study. Although they do not affect projections for how much sea level rise might happen in the future, he added.

The study authors said more work is needed to reevaluate global sea levels as well as the full implications of the risks posed to coastal communities now and in the future.

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