A study published in Nature found that the underestimation stems from a mismatch between how sea and land altitudes are measured, according to Philip Minderhoud of Wageningen University. Adjusting to a more accurate coastal height baseline means that if seas rise by a little more than 3 feet (1 meter), waters could inundate up to 37% more land and threaten 77 million to 132 million more people, the study reported. Sea levels have accelerated since the 1960s, according to a single source, Ola Kalén, an oceanographer at SMHI, as reported by Aftonbladet. The same source said seas could rise by up to 150 centimeters.
Separate research in Science Advances provides detailed risk assessments for U.S. coasts. It found that 17.5 million people along the Atlantic and Gulf coasts are at 'very high' risk of flooding, and an additional 17 million are at 'high' risk. In New York City, 4.75 million people fall into the two highest risk levels for all flooding, with more than 200,000 buildings likely to be damaged. In New Orleans, 99% of the city's population—about 380,000 people—is at risk, the study said. Jacksonville has 679,000 people at high or very high risk.
Sea level has accelerated since the 1960s. It's shocking how fast it's going in the wrong direction.
The exact economic costs of the underestimated flood risk remain unclear, as do the specific adaptation measures being considered. The relationship between the two studies in terms of methodology and scope has not been fully detailed.