Oceans are rising – but when?
The original version from This story appeared in Quanta Magazine.
In May 2014, NASA announced at a press conference that part of the West Antarctic Ice Sheet appears to have reached the point of irreversible retreat. Glaciers that flow seaward at the edge of the 2-kilometer-thick ice sheet are losing ice faster than snowfall can replenish them, causing their edges to dry inward. That being said, the question was no longer if the West Antarctic Ice Sheet would disappear, but when. When these glaciers disappear, sea levels will rise by more than a meter, flooding the land currently inhabited by 230 million people. And it’s the first step before the entire ice sheet collapses, which could raise seas by 5 meters and redraw the world’s coastlines.
At the time, scientists assumed that the loss of these glaciers would unfold over centuries. But in 2016, a bomb study in nature They concluded that collapsing ice shelves could cause the escape process to retreat, dramatically speeding up the timeline. The Intergovernmental Panel on Climate Change (IPCC) found out and created a new worst-case scenario: by 2100, meltwater from Antarctic, Greenland, and mountain glaciers combined with thermal expansion of seawater could raise global sea levels by more than 2 meters. And this will only be the beginning. If greenhouse gas emissions continue unabated, seas will rise by 15 meters by 2300.
However, not all scientists are convinced by the escape scenario. Thus, a tension has arisen about how long we have until the great glaciers of West Antarctica disappear. If their retreat unfolds over the centuries, humanity may have time to adjust. But if rapid destabilization begins in the coming decades through the controversial runaway process, the consequences could outpace our ability to respond. Scientists warn that major population centers — New York, New Orleans, Miami and Houston — may not be ready.
“We certainly haven’t ruled it out,” said Karen Alley, a glaciologist at the University of Manitoba whose research supports the possibility of an escape process. “But I’m not ready to say it’s going to happen anytime soon. Nor am I going to say it can’t happen.”
For thousands of years, humanity has thrived along the coast, oblivious to the fact that we live in a geologic accident—an unusual spell of shallow seas. The oceans will return, but how soon? What does science say about how the ice sheets are retreating, and therefore, about the future of our ports, our homes and the billions of people who live near the coast?
Landed by the sea
In 1978, John Mercer, a glaciologist extraordinaire at Ohio State University who apparently conducted fieldwork in bare feet, was one of the first to predict that global warming would threaten the West Antarctic Ice Sheet. He based his theory on the ice sheet’s unstable relationship with the sea.
Larger than Alaska and Texas combined, West Antarctica is separated from the eastern half of the continent by the Trans-Southeast Mountains, whose peaks are buried up to the chin in ice. Unlike East Antarctica (and Greenland), where most of the ice is on land above water, in West Antarctica, the ice sheets form a bowl-shaped depression deep below the sea surface, with seawater at its edges. This makes the West Antarctic Ice Sheet the most vulnerable to collapse.
A piled-up dome of ice, the ice sheet flows outward under its own weight through tentacle-like glaciers. But glaciers do not stop at the coastline. Instead, huge floating sheets of ice hundreds of meters thick spread over the sea. These “ice shelves” are like giant floating rafts, held together by traction forces and contact with underwater ridges and ridges. They make the glaciers resistant to the inevitable gravitational pull towards the sea.
