A glacier the size of the United Kingdom or the State of Florida may well shatter within three to five years and trigger a domino effect collapsing the great floating ice platforms across West Antarctica warns the International Thwaites Glacier Collaboration.
The collapse does not mean that sea levels will inundate coastal cities soon; the marine extension is already floating. Instead, it means that the loss of the eastern half of the ice shelf currently stuck on a ridge in combination with the current rapid breakup of the western half will begin the process of land ice flowing into the Amundsen Sea. The land ice of Thwaites ice stream holds two feet of sea-level rise. It could take decades to centuries for all that ice to threaten the world's cities, but it will rise much more rapidly than previously thought.
Currently, the loss of freshwater from Thwaites contributes four percent to global sea rise. The loss of the ice shelf will increase that number to 25% due to the observed changes. Other Antarctica glaciers are also a threat to civilization, as are Greenland and mountain glaciers, all of which are rapidly melting from human-caused global heating.
Scientists have discovered a series of worrying weaknesses in the ice shelf holding back one of Antarctica's most dangerous glaciers, suggesting that this important buttress against sea level rise could shatter within the next three to five years.
Until recently, the ice shelf was seen as the most stable part of Thwaites Glacier, a Florida-sized frozen expanse that already contributes about 4 percent of annual global sea level rise. Because of this brace, the eastern portion of Thwaites flowed more slowly than the rest of the notorious "doomsday glacier."
But new data show that the warming ocean is eroding the eastern ice shelf from below. Satellite images taken as recently as last month and presented Monday at the annual meeting of the American Geophysical Union show several large, diagonal cracks extending across the floating ice wedge.
These weak spots are like cracks in a windshield, said Oregon State University glaciologist Erin Pettit. One more blow and they could spiderweb across the entire ice shelf surface.
"This eastern ice shelf is likely to shatter into hundreds of icebergs," she said. "Suddenly the whole thing would collapse."
The failure of the shelf would not immediately accelerate global sea level rise. The shelf already floats on the ocean surface, taking up the same amount of space whether it is solid or liquid.
But when the shelf fails, the eastern third of Thwaites Glacier will triple in speed, spitting formerly landlocked ice into the sea. Total collapse of Thwaites could result in several feet of sea level rise, scientists say, endangering millions of people in coastal areas.
Paul Voosen also writes on the news in Science recently presented to the American Geophysical Union.
The most dramatic sign of impending failure is a set of diagonal fractures that nearly span the entire shelf. Last month, satellites spotted accelerating movement of ice along the fractures, says Erin Pettit, a glaciologist at Oregon State University, Corvallis, who is part of a multiyear expedition studying the glacier. The shelf is a bit like a windshield with a series of slowly opening cracks, she says. “You’re like, I should get a new windshield. And one day, bang—there are a million other cracks there.”
Once the ice shelf shatters, large sections of the glacier now restrained by it are likely to speed up, says Ted Scambos, a glaciologist at the University of Colorado, Boulder, and a leader of the Thwaites expedition. In a worst case, this part of Thwaites could triple in speed, increasing the glacier’s contribution to global sea level in the short term to 5%, Pettit says.
Even more worrisome is the process that has weakened the ice shelf: incursions of warm ocean water beneath the shelf, which expedition scientists detected with a robotic submersible. Because Thwaites sits below sea level on ground that dips away from the coast, the warm water is likely to melt its way inland, beneath the glacier itself, freeing its underbelly from bedrock. A collapse of the entire glacier, which some researchers think is only centuries away, would raise global sea level by 65 centimeters. And because Thwaites occupies a deep basin into which neighboring glaciers would flow, its demise could eventually lead to the loss of the entire West Antarctic Ice Sheet, which locks up 3.3 meters of global sea level rise. “That would be a global change,” says Robert DeConto, a glaciologist at the University of Massachusetts, Amherst. “Our coastlines will look different from space.”
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