Sea levels are much higher than previously thought due to

Sea level rise caused by climate change may be significantly higher than previously thought, according to a new study, which says a “methodological blind spot” led researchers to underestimate existing coastal water levels. The revelation suggests that the highest seas threaten tens of millions more people than scientists and government officials believed, with elevated risks to already vulnerable communities.

The new research, published in the journal Nature, reviewed hundreds of scientific studies and hazard assessments, estimating that about 90% of them underestimated coastal water reference heights by an average of 1 foot. The study found that it is a much more common problem in the Global South, the Pacific and Southeast Asia, and less in Europe and along the Atlantic coasts.

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

In the new study, he and his co-authors wrote that their goal was to eliminate the continued use of incorrect methodologies and what they called “widespread underestimations of coastlines.” [sea level rise] and hazard impact assessments.”

Each way of calculating sea and land altitudes measures those areas appropriately, he said. But when sea meets land, there are many factors that are often not taken into account when using satellites and Earth models.

Studies that calculate the impact of sea level rise typically “don’t take into account the actual measured sea level, so they used 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 close to 3 feet, Minderhoud said.

A simple way to understand it is that many studies assume sea levels without waves or currents, when the reality at the water’s edge is that the oceans are constantly churned by wind, tides, currents and changes in temperature. and things like El Niñothe authors said.

Sticking to a more accurate coastal height baseline means that if seas rise just over 3 feet (as some studies suggest they will by the end of the century), the waters could inundate up to 37% more land and threaten between 77 and 132 million more people, according to the study.

That would cause problems in planning and paying for the impacts of a warming world.

people at risk

“There are many people here for whom the risk of extreme flooding is much higher than previously 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 largest discrepancy, has the largest number of people already threatened by rising sea levels, he said.

Minderhoud noted that the island nations of that region are one area where the reality of the discrepancy hits home.

For Vepaiamele Trief, a 17-year-old climate activist, the projections are not abstract. On its home island in the South Pacific archipelago of Vanuatu, the coast has visibly receded in its short life, with beaches eroded, coastal trees uprooted and some houses now just 3 feet from the sea at high tide. On Ambae Island, where his grandmother lives, a coastal road linking the airport to his village has been diverted inland due to encroaching water. Graves have been submerged and entire lifestyles feel threatened.

“These studies are not just words written on paper. They are not just numbers. They are people’s real livelihoods,” he said. “Put yourself in the shoes of our coastal communities: their lives will be completely disrupted due to sea level rise and climate change.”

This new study is more or less about what the truth on the ground is.

Calculations that may be correct for the seas in general or for land are not entirely correct at that key point of intersection of water and land, Seeger and Minderhoud said. It is especially true in the Pacific.

“To understand how much higher a piece of land is than the water, you need to know the elevation of the land and the elevation of the water. And what this paper says the vast majority of studies have done is simply assume that zero in their land elevation data set is the water level. When in reality, it is not,” said sea level rise expert Ben Strauss, executive director of Climate Central. Their 2019 study was one of the few that, according to the new paper, got it right.

“People are just wrong from the starting point,” said Strauss, who was not involved in the research.

Maybe it’s not so bad, some scientists say

Other outside scientists said Minderhoud and Seeger may be making too much of the problem.

“I think they are slightly exaggerating the implications for impact studies: the problem is actually well understood, although it is addressed in a way that could probably be improved,” said Gonéri Le Cozannet, a scientist at the French geological survey. Most local planners know their coastal problems and plan accordingly, said Rutgers University sea level expert Robert Kopp.

That’s true in Vietnam in the high-impact zone, Minderhoud said. They have a precise sense of elevation, he said.

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

Taken together, the studies suggest that governments may be planning for coastal and climate risks with an incomplete picture of how the ocean is changing.

“When the ocean comes closer, it takes away more than just the land we used to enjoy,” said Thompson Natuoivi, climate advocate for Save the Children Vanuatu.

“Sea level rise is not only changing our coast, but our lives. We’re not talking about the future, we’re talking about right now.”