The sea is higher than we thought and millions more are at risk, study finds

Climate change's rising seas may threaten tens of millions more people than scientists and government planners originally thought because of mistaken research assumptions on how high coastal waters already are, a new study said. Researchers studied hundreds of scientific studies and hazard assessments, calculating that about 90% of them underestimated baseline coastal water heights by an average of 1 foot (30 centimeters), according to the study in the journal Nature. It's a far more frequent problem in the Global South, the Pacific, and Southeast Asia, and less so in Europe and along Atlantic coasts. The cause is a mismatch between the way sea and land altitudes are measured, said study co-author Philip Minderhoud, a hydrogeology professor at Wageningen University & Research in the Netherlands. And he attributed that to a “methodological blind spot” between the different ways those two things are measured. Each way measures its own areas properly, he said. But where sea meets land, there are a lot of factors that often don't get accounted for when satellites and land-based models are used. Studies that calculate sea level rise impact usually “do not look at 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 (1 meter), Minderhoud said. One simple way to understand that is that many studies assume sea levels without waves or currents, when the reality at the water's edge is of oceans constantly roiled by wind, tides, currents, changing temperatures, and things like El Niño, said Minderhoud and Seeger. Adjusting to a more accurate coastal height baseline means that if seas rise by a little more than 3 feet (1 meter)—as some studies suggest will happen by the end of the century—waters could inundate up to 37% more land and threaten 77 million to 132 million more people, the study said. That would trigger problems in planning and paying for the impacts of a warming world. This article was provided by The Associated Press.