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It's speeding up.
Antarctica's Pine Island Glacier, already the biggest source of sea level rise from the ice-clad continent, has started purging more ice than ever observed (from it) into the ocean.
In research recently published in the journal Science Advances,glacier experts found Pine Island — which holds some 180 trillion tons of ice — lost big chunks of ice into the sea over the past few years (2017-2020), and the glacier picked up its pace. This means Pine Island continues to recede, weaken, and expel bounties of ice into the ocean, with the potential to add much more sea level rise to the planet's already problematic sea level woes. (Earth's sea levels have already risen by some eight to nine inchessince 1880, and they're now accelerating.)
"It's not what you want to see," said Ian Joughin, a glaciologist at the University of Washington and an author of the research.
Pine Island's acceleration, resulting in more ice going into the ocean, is clear:
Between 1992 and 2009 the glacier accelerated from 2.5 to 4 kilometers (1.5 to 2.5 miles) per year.
Between 2010 and 2016 the rate stayed steady at some 4 km (2.5 miles) per year.
Between 2017-2020 it accelerated again to 4.5 km (2.8 miles) per year.
The retreating ice comes from the end of the glacier that reaches over the ocean, called an ice shelf. Crucially, ice shelves ground themselves to the ocean floor, acting somewhat like "a cork in a bottle" to hold back the rest of colossal glaciers from flowing unimpeded into the sea. So if the ice shelf eventually goes, so can the glacier (over time).
Over the past few years, detailed satellite observations show Pine Island Glacier's ice shelf lost20 percent of its mass, explained Joughin. After around two decades of thinning and retreat, large chunks at the glacier's weakened edge broke into the ocean, allowing Pine Island to speed up by 12 percent. This doesn't spell immediate catastrophe, Joughin cautioned, but it underscores how ice shelves in West Antarctica are gradually losing more ice and incrementally falling apart. It's like the gradual collapse of the Roman Empire — a long process, not a sudden avalanche.
"It's in a state of collapse," explained Joughin. The key question is how quickly the ice shelf, followed by the rest of the glacier, might break or collapse into the sea. That's why retreating Antarctic ice shelves are such a vigorous area of climate research. If the Pine Island Glacier — which by itself has enough ice to raise sea levels by over a foot and a half — and nearby glaciers collapse over the next century or two, the permanent floods would bode much worse for civilization (especially low-lying lands like Florida) than if this happened more gradually, over the course of perhaps 1,000 years.
"It's a matter of how fast," emphasized Joughin.
That speed is a daunting challenge to predict.
"It's a matter of how fast."
The new observations certainly show that Pine Island's "ice shelf is weakening, thinning, and retreating," said Stef Lhermitte, a geoscientist specializing in remote sensing at the Netherlands' Delft University of Technology who researches the Pine Island Glacier. (Lhermitte had no involvement with the new research.) "Yet quantifying the future timing and magnitude of these changes or instabilities remains difficult," he noted, as the glacier's complex processes (like how quickly it might lose its grounding to the ocean floor) are uncertain.
What's pretty certain, however, is that major ice shelves in West Antarctica, namely Pine Island and the Florida-sized Thwaites Glacier next door, are weakening as the climate warms (largely as relatively warmer waters erode the ice shelves from below). Together, these glaciers could create many feet of sea level rise over the coming centuries. Thwaites' essential "grounding zone," for example, has been retreating back by around half a mile each year. "It is a tremendous rate of retreat," Sridhar Anandakrishnan, a professor of glaciology at Penn State University, told Mashable last year. "Thwaites is the one spot in Antarctica that has the potential to dump an enormous amount of water into the ocean over the next decades," he added.
As for Pine Island, Joughin notes "it's a longshot" that the shelf collapses in the next decade, though it's possible. The ice shelf is some 40 to 50 kilometers (25 to 31 miles) long, and naturally wavers back and forth within its longer receding trend. It could potentially readvance some in the coming years (meaning it gains more ice than it loses), though the thinned glacier growing significantly looks unlikely right now, said Joughin.
The 20-second clip below shows the Pine Island Glacier losing ice between 2015 and 2020. The second clip shows a decades-long retreating trend.
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Today, Pine Island is raising sea levels by one-sixth of a millimeter each year, "which may sound like a small number but it adds up over time," noted Joughin. This number is expected to continue increasing.
Crucially, Pine Island is only one (accelerating) source of sea level rise. Overall, global sea levels are now rising by some 3.6 millimeters per year, which is two-and-a-half times faster than rates during the 20th century. A conservative estimate, from the UN's Intergovernmental Panel on Climate Change(IPCC), is that sea levels will rise by another one to two feetby the century's end. But, this could very well be more like two or three feet, or potentially more.
What's next
Glacier and ice sheet experts, like Lhermitte and Joughin, will continue to carefully observe glaciers like Pine Island and Thwaites. Though Antarctica is profoundly remote and difficult to regularly visit, European Space Agency satellites now capture detailed, invaluable images of these glaciers every six days.
Already, Pine Island's visible speed-up and ice loss is "obviously not good news for sea level rise contributions," said Lhermitte. This activity demands more research, he said.
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In the coming decade, we'll be watching what happens. Expect to see a lot more satellite imagery, along with published science. It's clear that an extremely remote region at the bottom of the world holds large sway over what will become of Earth's sea levels this century — and beyond.