Sea levels are much higher than previously thought because of a “pathway blind spot,” study finds

Rising sea levels caused by climate change may be much higher than previously thought, according to a new study, which says a “methodological blind spot” has led researchers to underestimate current coastal water levels. Revelation suggests that the high seas they threaten tens of millions more people than scientists and government officials believed, with higher risks to already vulnerable communities.

A new study, published in the journal Nature, reviewed hundreds of scientific studies and risk assessments, calculating that nearly 90% of them underestimated the height of the base water by an average of 1 foot. Research has found it to be a very common problem Global South, Pacific and Southeast Asia, and less in Europe and on the Atlantic coast.

It’s because of differences between the way sea level and land level are measured, said study co-author Philip Minderhoud, a professor of hydrogeology at Wageningen University & Research in the Netherlands. He said that’s due to a “methodological blind spot” between the different ways those two things are measured.

In this new study, he and his co-authors wrote that their goal was to end the continued use of inappropriate methods and what they called “the widespread underestimation of the coast. [sea level rise] and risk impact assessment.”

Each method of calculating the height of sea and land measures those areas correctly, he said. But where the ocean meets the land, there are many factors that are often not accounted for when using satellite and earth-based models.

Studies that calculate the impact of sea level rise often “don’t look at the actual measured sea level so they use this zero-meter figure” as a starting point, said lead author Katharina Seeger of the University of Padua in Italy. In some places in the Indo-Pacific, it’s closer to 3 feet, Minderhoud said.

Another easy way to understand that is that most studies assume sea levels without tides or currents, when the reality at the water’s edge is oceans that are constantly being moved by wind, waves, currents, temperature changes. and things like El Niñosaid the authors.

Adapting to a more accurate baseline of coastal elevation means that if seas rise slightly more than 3 meters – as some studies suggest will happen by the end of the century – water could invade more than 37% of the land and threaten 77 million to 132 million people, the study said.

That can create problems in planning and accounting for the impacts of global warming.

Vulnerable people

“You have so many people here that the risk of severe flooding is much higher than people thought,” said Anders Levermann, a climate scientist at the Potsdam Institute for Climate Impacts Research in Germany, who was not part of the study. And Southeast Asia, where the study finds the biggest difference, has the most people already threatened by sea level rise, he said.

Minderhoud pointed to the island nations in that region as a place where the reality of difference hits home.

For Vepaiamele Trief, a 17-year-old climate activist, this statement is not incomprehensible. In his home on an island in the south Pacific islands of Vanuatu, the coast has already receded in the short time of his life, with beaches eroded, coastal trees uprooted and some homes now about 3 meters from the sea when the waves are big. On his grandmother’s island of Ambae, the coastal road from the airport to his village has been moved inland due to flooding. Graves have sunk and all ways of life are in danger.

“These courses are not just words written on paper. They are not just numbers. They are the real way of life for people,” he said. “Put yourself in the shoes of our coastal communities – their lives will be completely destroyed by sea level rise and climate change.”

This new research is about what is the truth on the ground.

Statistics that may be good for the ocean as a whole or for the land are not good for that important point where water and land meet, Seeger and Minderhoud said. It is especially true in the Pacific.

“In order to understand how much a piece of land is higher than the water, you need to know the height of the land and the height of the water. And what this paper says is that most of the studies that have been done just assume that the zero in your dataset of the height of the land is the water level. When in fact, it is not,” said sea level expert Ben Strauss, CEO of Climate Central. His 2019 study was one of the few new papers that got it right.

“It’s just a basic premise that people go astray,” said Strauss, who was not part of the study.

Maybe it’s not so bad, say some scientists

Some outside scientists say Minderhoud and Seeger may be making too much of a problem.

“I think they exaggerate the impact of the impact studies a little bit – the problem is well understood, although it can be fixed in a way that could be improved,” said Gonéri Le Cozannet, a scientist at the French geological survey. Most landscape planners know their coastal issues and plan accordingly, said Rutgers University sea level expert Robert Kopp.

That’s true in Vietnam in a high-impact area, Minderhoud said. They have an intuitive sense of superiority, he said.

The findings come as a new UNESCO report warns of major gaps in understanding how much carbon is being absorbed by the oceans. That report said the models differed by 10% to 20% in estimating the size of that carbon sink, raising questions about the accuracy of the global climate projections that depend on them.

Together, the research suggests that governments may be planning for coastal and climate risks with an incomplete picture of how the ocean is changing.

“When the sea gets closer, it takes more than just the area we were enjoying,” said Thompson Natuoivi, climate advocate for Save the Children Vanuatu.

“Sea level rise isn’t just changing our coastlines, it’s changing our lives. We’re not talking about the future – we’re talking about the present.”