Scientists said the rise in sea level, up to 12 feet, will take centuries to reach its peak and cannot be reversed. But they said a decrease in greenhouse gas emissions could slow the melt, while an increase could speed it slightly.

Warm, naturally occurring ocean water flowing under the glaciers is causing the melt. “We feel it is at the point that it is . . . a chain reaction that’s unstoppable,” regardless of any future cooling or warming of the global climate, said Eric Rignot, a professor of Earth science at the University of California at Irvine. He was the lead author of a NASA-funded study that was one of the two studies released Monday.

The only thing that might have stopped the ice from escaping into the ocean and filling it with more water “is a large hill or mountains,” Rignot said. But “there are no such hills that can slow down this retreat,” he added.