New York, Nov 13 (IANS): A vast ice sheet in northeast Greenland has begun a phase of fast ice loss, contributing to destabilisation that will cause global sea-level rise for decades to come, warns a new study.

Since 2012 warmer air and sea temperatures have caused the Zachariæ Isstrom ice sheet to "retreat rapidly along a downward-sloping, marine-based bed," the study said.

By itself, the Zachariæ Isstrom glacier holds enough water to trigger a half-metre rise in ocean levels around the world.

"The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is occurring at its grounding line," the authors wrote.

"Ice loss is happening fast in glaciological terms, but slow in human terms -- not all in one day or one year," said one of the researchers John Paden, associate professor at University of Kansas in the US.

For the study, the researchers crunched data acquired by University of Kansas-based Center for Remote Sensing of Ice Sheets (CReSIS) during NASA's Operation IceBridge and previous NASA flights over Greenland, including decades-old measurements of Zachariæ Isstrom.

"Within a few generations, ice loss could make a substantial difference in sea levels," Paden said.

"When you add up all the glaciers that are retreating, it will make a difference to a large number of people. Sea level has increased some over the last century, but only a small number of people have been affected compared to what is likely to come," Paden pointed out.

The study appeared in Science magazine.