Antarctica Ice Sheet Melting - “Nothing to stop it now"

Two groups of scientists reported Monday that seas across the earth will rise at least 10 feet over the next century or so mostly because of global warming. The finding, which had been feared by some scientists for decades, appears now to be inevitable.

The scientists say that the rise may continue to be relatively slow for at least the next century or so, but sometime after that it will probably speed up so sharply as to become a crisis. “This is really happening,” said Thomas P. Wagner, who runs NASA’s programs on polar ice and helped oversee some of the research. “There’s nothing to stop it now. But you are still limited by the physics of how fast the ice can flow.” 

Two papers scheduled for publication this week, in the journals Science and Geophysical Research Letters, attempt to make sense of an accelerated flow of glaciers seen in parts of West Antarctica in recent decades. Both papers conclude that warm water upwelling from the ocean depths has most likely triggered an inherent instability that makes the West Antarctic ice sheet vulnerable to a slow-motion collapse. And one paper concludes that factors some scientists had hoped might counteract such a collapse will not do so.

The new finding appears to be the fulfillment of a prediction made in 1978 by eminent glaciologist John H. Mercer of the Ohio State University. He outlined the uniquely vulnerable nature of the West Antarctic ice sheet and warned that the rapid human 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 Dr. Mercer predicted. (He died in 1987.)

Most scientists in the field see a connection between the stronger winds and human-caused global warming, but they say other factors are likely at work, too. Natural variability of climate may be one of them. Another may be the ozone hole over Antarctica, caused by an entirely different environmental problem, the human release of ozone-destroying gases.

Whatever the mix of causes, they appear to have triggered a retreat of the ice sheet that can no longer be stopped, even if the factors drawing in the warmer water were to reverse suddenly, the scientists said. At this point, a decrease in the melt rate back to earlier levels would be “too little, too late to stabilize the ice sheet,” said Ian Joaquin, a glaciologist at the University of Washington and lead author of the new paper in Science. “There’s no stabilization mechanism.”

Richard B. Alley, a climate scientist at Pennsylvania State University who was not involved in the new research but has studied the polar ice sheets for decades, said he found the new papers compelling. Though he has long feared the possibility of ice-sheet collapse, when he learned of the new findings, “it shook me a little bit,” Dr. Alley said. He added that while a large rise of the sea may now be inevitable from West Antarctica, continued release of greenhouse gases will almost certainly make the situation worse. The heat-trapping gases could destabilize other parts of Antarctica as well as the Greenland ice sheet, causing enough sea-level rise that many of the world’s coastal cities will eventually have to be abandoned.