Rising sea levels due to climate change could threaten tens of millions more people than scientists and government planners originally thought, a new study says. This is already due to incorrect research assumptions about the height of coastal waters.
The researchers studied hundreds of scientific studies and risk assessments and calculated that about 90% of them underestimated baseline coastal water levels by an average of 1 foot (30 centimeters). Wednesday’s study published in the journal Nature. It is a much more common problem in the Global South, the Pacific, and Southeast Asia, but less so in Europe and the Atlantic coast.
Study co-author Philip Minderhoud, a professor of hydrogeology at Wageningen University Research in the Netherlands, said the cause was a discrepancy in how sea and land altitudes are measured. And he blamed it on a “methodological blind spot” between different ways of measuring these two things.
Each method measures each area properly, he said. However, where the ocean meets land, there are many factors that are not considered when using satellite or land models. Studies calculating the effects of sea level rise typically “use this zero meter figure as a starting point because they don’t take into account the actual measured sea level,” said lead author Catalina Seeger from the University of Padua in Italy. In some parts of the Indo-Pacific region, the water can be nearly 3 feet (1 meter) deep, Minderhoud said.
Dirkshan Kumara stands beside the remains of his family’s home and looks out to sea in Iranaweera, Sri Lanka, June 15, 2023. (AP Photo/Eranga Jayawardena, File)
Dirkshan Kumara stands beside the remains of his family’s home and looks out to sea in Iranaweera, Sri Lanka, June 15, 2023. (AP Photo/Eranga Jayawardena, File)
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One easy way to understand that is that while many studies assume an ocean surface with no waves or currents, the reality at the water’s edge is an ocean that is constantly turbulent due to wind, tides, ocean currents, temperature changes, El Niño, and more, Minderhoud and Seeger said.
Adjusting to a more accurate coastal elevation baseline means that this will happen if sea levels rise by a little more than 3 feet (1 meter), as some studies have suggested. by the end of the century — The likelihood of water flooding could increase by up to 37%, potentially threatening an additional 77 million to 132 million people, the study says.
That would create problems in planning for and paying for the effects of a warming world.
people at risk
“There are a lot of people here who are at much higher risk of extreme flooding than people thought,” said Anders Levermann, a climate scientist at Germany’s Potsdam Institute for Climate Impact Research, who was not involved in the study, but said he found the most discrepancies in Southeast Asia, where the most people are already under threat from rising sea levels.
Mr. Minderhoud pointed to the region’s island countries as an area where contradictions are brought to light.
Children play on an uprooted tree along a beach in Mele, Vanuatu, on July 19, 2025. Once lush with vegetation, much of it has now been lost to storms, erosion, and other environmental pressures. (AP Photo/Annika Hammerschlag, File)
Children play on an uprooted tree along a beach in Mele, Vanuatu, on July 19, 2025. Once lush with vegetation, much of it has now been lost to storms, erosion, and other environmental pressures. (AP Photo/Annika Hammerschlag, File)
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For 17-year-old climate activist Vepaiamere Trief, predictions are not abstract. During her short lifetime, the coastline of her home island in the Vanuatu archipelago in the South Pacific has visibly receded, beaches have eroded, coastal trees have been uprooted, and some homes are just 3 feet from the ocean at high tide. On Ambae Island, where her grandmother lives, the coastal road from the airport to the village has been rerouted inland due to flooding. Their graves are underwater and they feel their entire way of life is under threat.
“These studies aren’t just words on paper. They’re not just numbers. They’re people’s real lives,” she said. “Put yourself in the shoes of the people of our coastal communities, whose lives will be completely turned upside down by sea level rise and climate change.”
Be careful where you start
This new study pretty much says what the truth on the ground is.
Seeger and Minderhoud said calculations that may be correct for the entire ocean or land are simply not correct at critical intersections between water and land. This is especially true in the Pacific.
On July 18, 2025, a tombstone submerged underwater on Pele Island in Vanuatu, a country hit hard by rising sea levels. (AP Photo/Annika Hammerschlag, File)
On July 18, 2025, a tombstone submerged underwater on Pele Island in Vanuatu, a country hit hard by rising sea levels. (AP Photo/Annika Hammerschlag, File)
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“To understand how high land is above water, you need to know the land elevation and the water elevation, and the majority of the research this paper says simply assumes that zero in the land elevation dataset is water level, which is not the case,” said Ben Strauss, CEO of sea level rise expert Climate Central. his 2019 survey He was one of the few to say he got the new paper right.
“We just start with a baseline of what people misunderstand,” said Strauss, who was not involved in the study.
Maybe it’s not that bad, some scientists say
Other outside scientists said Minderhoud and Seeger may be making the problem too big.
“I think they are slightly exaggerating the impact on impact research. The problem is actually well understood, although it is being addressed in ways that can probably be improved,” said Gonelli Le Cozanet, a scientist at the French Geological Survey. Most local planners are aware of coastal issues and plan accordingly, said Robert Kopp, a sea level expert at Rutgers University.
The same is true in Vietnam, a highly affected region, Minderhoud said. They have an accurate sense of altitude, he said.
The discovery comes as a new UNESCO report warns of major gaps in our understanding of how much carbon the ocean absorbs. The report found that models differed by 10% to 20% in estimating the size of carbon sinks, raising questions about the accuracy of model-dependent global climate projections.
The coastline of Efate Island, Vanuatu, seen on July 19, 2025. (AP Photo/Annika Hammerschlag, File)
The coastline of Efate Island, Vanuatu, seen on July 19, 2025. (AP Photo/Annika Hammerschlag, File)
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Together, these studies suggest that governments may be planning for coastal and climate risks with an incomplete understanding of how the ocean is changing.
“When we move closer to the ocean, we are taking away more than the land that we used to enjoy,” said Thompson Natuoibi, a climate change advocate with Save the Children Vanuatu.
“Sea level rise doesn’t just change coastlines, it changes our lives. We’re not talking about the future, we’re talking about now.”
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