Sea-level rise is accelerating around the world, thanks to ongoing melting of ice sheets in both Antarctica and Greenland, a new study suggests.
At the current rate of melting, the world's seas will be at least 2 feet higher by the end of the century compared to today, according to research published in the Proceedings of the National Academy of Sciences.
Such a rise could leave portions of the world’s coastal cities underwater. It would also increase high tides and worsen storm surges.
"This acceleration ... has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate — to more than (2 feet) instead of about (1 foot)." said Steve Nerem, the study lead author and a professor of aerospace engineering sciences at the University of Colorado in Boulder.
"And this is almost certainly a conservative estimate," he added.
Scientists looked 25 years of satellite data to calculate the levels of Earth's seas.
Sea-level rise, one of the most clear-cut signals of global warming, has risen nearly 8 inches worldwide since 1880 but, unlike water in a bathtub, it doesn't rise evenly.
In the past 100 years, it has climbed about a foot or more in some U.S. cities because of ocean currents and the natural settling of land — 11 inches in New York and Boston, 12 in Charleston, 16 in Atlantic City, 18 in Norfolk and 25 in Galveston, Texas, according to a USA TODAY analysis of tide gauge data collected by the National Oceanic and Atmospheric Administration.
Here's why: As the Earth's temperature warms, so do the seas. Heat-trapping greenhouse gases cause more land ice — glaciers and ice sheets — to melt and water to expand. Warmer water simply takes up more room than cooler water.
Of the 3 inches of sea-level rise in the past quarter century, about 55% is from warmer water expanding, and the rest is from melting ice.
Scientists say global warming will be the primary cause of future sea-level rise. The greatest uncertainty is just how quickly the massive West Antarctic ice sheet will melt.
"This study highlights the important role that can be played by satellite records in validating climate model projections," said co-author John Fasullo, a climate scientist at the National Center for Atmospheric Research.
Greenland has caused three times more sea-level rise than Antarctica so far, but ice melt on the southern continent is responsible for more of the acceleration.
"Antarctica seems less stable than we thought a few years ago," Rutgers climate scientist Robert Kopp said.
Penn State climate scientist Michael Mann, who was not involved with the study, told CNN that "it confirms what we have long feared: that the sooner-than-expected ice loss from the west Antarctic and Greenland ice sheets is leading to acceleration in sea level rise sooner than was projected."
Contributing: The Associated Press