NEW YORK —
Global warming caused by the human-driven release of greenhouse gases has helped to destabilize the ice sheet, though other factors may also be involved, the scientists said.
The rise of the sea is likely to continue to be relatively slow for the rest of the 21st century, the scientists added, but in the more distant future it may accelerate markedly, potentially throwing society into crisis.
“This is really happening,” Thomas P. Wagner, who runs NASA’s programs on polar ice and helped oversee some of the research, said in an interview. “There’s nothing to stop it now. But you are still limited by the physics of how fast the ice can flow.”
Two scientific papers released by the journals Science and Geophysical Research Letters came to similar conclusions by different means. Both groups of scientists found that West Antarctic glaciers had retreated far enough to set off an inherent instability in the ice sheet, one that experts have feared for decades. NASA called a telephone news conference Monday to highlight the urgency of the findings.
The West Antarctic ice sheet sits in a bowl-shaped depression in the Earth, with the base of the ice below sea level. Warm ocean water is causing the ice along the rim of the bowl to thin and retreat. As the front edge of the ice pulls away from the rim and enters deeper water, it can retreat much faster than before.
In one of the new papers, a team led by Eric Rignot, a glaciologist at the University of California Irvine, used satellite and air measurements to document an accelerating retreat over the past several decades of six glaciers draining into the Amundsen Sea region. And with updated mapping of the terrain beneath the ice sheet, the team was able to rule out the presence of any mountains or hills significant enough to slow the retreat.
“Today we present observational evidence that a large sector of the West Antarctic ice sheet has gone into irreversible retreat,” Rignot said in the NASA news conference. “It has passed the point of no return.”
Those six glaciers alone could cause the ocean to rise 4 feet as they disappear, Rignot said, possibly within a couple of centuries. He added that their disappearance will most likely destabilize other sectors of the ice sheet, so the ultimate rise could be triple that.
A separate team led by Ian Joughin of the University of Washington studied one of the most important glaciers, Thwaites, using sophisticated computer modeling, coupled with recent measurements of the ice flow. That team also found that a slow-motion collapse had become inevitable. Even if the warm water now eating away at the ice were to dissipate, it would be “too little, too late to stabilize the ice sheet,” Joughin said. “There’s no stabilization mechanism.”
The two teams worked independently, preparing papers that were to be published within days of each other. After it was learned that their results were similar, the teams and their journals agreed to release the findings on the same day.
The new finding appears to be the fulfillment of a prediction made in 1978 by an eminent glaciologist, John H. Mercer of the Ohio State University. He outlined the vulnerable nature of the West Antarctic ice sheet and warned that the rapid human-driven release of greenhouse gases posed “a threat of disaster.”
He was assailed at the time, but in recent years, scientists have been watching with growing concern as events have unfolded in much the way Mercer predicted. He died in 1987.