Ahmed Kamel – Egypt Daily News
Rising seas driven by climate change may threaten tens of millions more people than previously estimated, according to new research that suggests many scientific studies have underestimated how high coastal waters already are.
The study, published in the journal Nature, reviewed hundreds of scientific papers and hazard assessments and found that roughly 90 percent underestimated baseline coastal water levels by an average of about one foot. Researchers say the miscalculation stems from the way scientists typically measure the boundary where land meets the sea.
According to the authors, correcting this baseline could significantly alter projections of future flooding. If global sea levels rise by a little more than three feet by the end of the century a scenario considered plausible in many climate models, coastal flooding could affect up to 37 percent more land than previously projected and place an additional 77 million to 132 million people at risk.
Lead author Katharina Seeger of University of Padua said the issue largely stems from how sea level rise studies define “zero” when calculating coastal elevation.
“Studies that calculate sea level rise impact usually do not look at the actual measured sea level, so they use this zero-meter figure as a starting point,” Seeger explained.
Co-author Philip Minderhoud of Wageningen University & Research said the discrepancy results from a “methodological blind spot” between the ways land elevation and ocean levels are measured. Each system works accurately within its own framework, he said, but complications arise at the coastal boundary where the two systems intersect.
In reality, coastal waters rarely remain at a constant level. Waves, tides, currents, winds and climate patterns such as El Niño constantly alter water levels at the shoreline, meaning that the assumed baseline used in many studies does not reflect real-world conditions.
The research found the problem is particularly pronounced in parts of the Global South, especially across the Pacific and Southeast Asia, where discrepancies between assumed and actual coastal water levels can reach several feet. In some areas of the Indo-Pacific region, the difference may approach three feet, the researchers said.
Climate scientists say the revised projections could have major implications for governments planning coastal infrastructure, flood defenses and climate adaptation strategies.
“You have a lot of people here for whom the risk of extreme flooding is much higher than people thought,” said Anders Levermann of the Potsdam Institute for Climate Impact Research, who was not involved in the study. He noted that Southeast Asia already contains some of the world’s most densely populated coastal regions.
For many communities, the issue is not theoretical. On the Pacific island nation of Vanuatu, climate activist Vepaiamele Trief said rising seas are already reshaping daily life. Along parts of the coastline, beaches have eroded, trees have fallen into the sea and homes now sit just a few feet from the water during high tide. On the island of Ambae, she said a coastal road connecting the airport to her village has already been relocated inland due to encroaching waters, while some burial grounds have been submerged.
“These studies aren’t just numbers,” Trief said. “They’re people’s actual livelihoods.”
The study’s findings have drawn mixed reactions from other experts. Ben Strauss, CEO of Climate Central, said the research highlights a critical issue about how sea level measurements are interpreted.
“To understand how much higher a piece of land is than the water, you need to know both the land elevation and the water elevation,” Strauss said. “What this paper says is that the vast majority of studies assumed the zero point in land elevation datasets equals sea level when in fact it doesn’t.”
However, some scientists argue the new research may overstate the implications. Gonéri Le Cozannet of the French Geological Survey said the underlying issue is already recognized in coastal science, though he acknowledged that measurement methods could still be improved.
Similarly, Robert Kopp of Rutgers University said many local planners already account for complex coastal conditions when designing flood protections and adaptation plans.
Even so, researchers say the study underscores the importance of improving how scientists measure and model the dynamic zone where oceans meet land, an area that will play an increasingly critical role as climate change drives global sea levels higher throughout the 21st century.
