(CN) - A massive glacier melting quickly in Greenland could cause global sea levels to rise by more than 18 inches, scientists say in a new study in the journal Science.
Researchers from the University of California, Irvine and the University of Kansas found that the Zachariae Isstrom glacier, one of Greenland's largest ice sheets, is breaking apart and melting into the Atlantic Ocean, losing mass at a rate of 5 billion tons a year.
The glacier entered a phase of "accelerated retreat" in 2012 and has been calving enormous icebergs into the ocean, which will raise ocean levels for "decades to come," said lead author Jeremie Mouginot, an associate project scientist at UCI.
The bottom of the glacier is being rapidly eroded by warm ocean water mixed with growing amounts of meltwater from the surface of the ice sheet, according to the findings published in the Nov. 12 issue of Science.
Senior author Eric Rignot, chancellor's professor of earth system science at UCI, said that Zachariae Isstrom "is being hit from above and below."
Rignot and Mouginot were quoted in a statement about their research from the University of Kansas.
"The top of the glacier is melting away as a result of decades of steadily increasing air temperatures, while its underside is compromised by currents carrying warmer ocean water, and the glacier is now breaking away into bits and pieces and retreating into deeper ground," Rignot said.
Rignot said that researches have long wondered what a massive melt of the planet's large glaciers would do to sea levels.
"We no longer need to wonder; for a couple of decades now, we've been able to directly observe the results of climate warming on polar glaciers. The changes are staggering and are now affecting the four corners of Greenland," he said.
The research team used data from aerial surveys conducted by NASA's Operation IceBridge, and imagery from multiple international space agencies to study the large glacier.
Some of the satellite imagery dates back to 1975, said John Paden, an associate scientist for the Center for Remote Sensing of Ice Sheets, who helped analyze data about the thickness of the glacier's ice.
With that data, "You can look at what the ice shelf is doing, how it's shrinking over time. Satellite optical and radar imagery were used to measure surface-velocity changes over time," he said.
By itself, Zachariae Isstrom holds enough water to trigger a half-meter rise in ocean levels around the world, according to the research.
Another nearby glacier with an equal amount of ice, Nioghalvfjerdsfjorden, is also melting fast but is receding at a slower rate because it is protected by an uphill bed. Together, the two glaciers make up 12 percent of the Greenland ice sheet and would boost global sea levels by more than 39 inches if they fully collapsed, the researchers say.
"From a societal standpoint, the reason why there's so much focus on ice sheets is because predicted sea level rise will affect nearly every coastal country - the United States for sure, and low-lying countries with limited resources are likely to be the worst off," Paden said. "Mass displacements of potentially millions of people will affect countries that have no coastlines."
Paden said that scientists study ice sheets "to have an understanding of how soon things are likely to happen and to help us use our limited sources to help mitigate the problem."