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This originally appeared on Climate Central.


Sea level rise is a game of millimeters a year, but those millimeters add up to a huge amount of water entering the world’s oceans. And the rising tide could eventually swamp cities around the globe.

With tide gauges distributed sparsely around the planet, scientists have turned to satellites to provide a global picture of sea level since the early 1990s. New research published on Monday in Nature Climate Change refines those satellite estimates and provides some good and bad news. The good news? Total sea level rise is lower than previous estimates. The bad news? Sea level rise rates are speeding up.

Christopher Watson, a geodesist from the University of Tasmania, led the latest round of research that adjusts satellite readings taken from hundreds of miles above the Earth to measure small changes in sea level heights around the globe since the early 1990s.

“What’s striking is its (the study’s) consistency with future projections of sea level in the IPCC,” Watson said. “Those estimates state that there could be up to 98 centimeters (39 inches) of sea level rise by 2100. We’re certainly tracking on that upper bound of the IPCC projection and that projection to 2100 has significant impacts.”

That’s because sea level rise isn’t just a linear problem, it’s one predicated on tipping points for major damage in coastal areas unless efforts are made to adapt. Currently more than 1 billion people live along shorelines around the world and $11 trillion in assets sit below the 100-year flood mark on coasts, though that number could balloon to as much as $210 trillion by 2100. Sea levels have risen by about a foot since 1900 and the rise is projected to continue accelerating into at least the next century.

Many coastal cities in the U.S. already stand at the precipice of regular minor coastal flooding because of sea level rise. Some cities such as Baltimore and Honolulu have already taken the leap, with coastal flooding 10 times more likely than it was in 1930. By the 2050s, sea level rise is likely to cross a tipping point for 26 major U.S. cities, which can expect at least 30 days of “nuisance flooding” each year.