“I’m not really a catastrophist,” Joughin said. “But the integrity of the ice shelf is definitely in question.”
Previously, scientists had focused on the slow but steady thinning of the ice shelf as warm ocean waters seep underneath it. This melting makes ice shelves more vulnerable to collapse during the Antarctic summer, when high temperatures cause melting on the surface. But, since temperatures in West Antarctica are rarely more than a few degrees above freezing, that process was expected to take centuries to unfold.
What’s happening now is much faster and less predictable, Joughin said. It appears that the rapid slide of the glacier is creating fractures in the ice shelf, which leads to more pieces breaking off, or “calving.” Computer simulations and mathematical models support the idea that this process is responsible for the glacier’s speedup.
Pine Island’s ice shelf used to calve every four to six years, according to NASA, but since 2017 it has lost huge chunks of ice every year. Radar instruments on board the European Space Agency’s Sentinel-1 satellites capture images of the glacier every six days, even amid the months-long darkness of Antarctic winter. This allows scientists to watch the ice shelf break up in almost real time.
Just two years later, more bergs broke off along the ice shelf’s “shear margin,” where it attaches to thicker ice along the sides of the bay.
It’s as if the cork in the bottle containing Pine Island glacier is crumbling. Having lost contact with the sides of the bay, the shelf is giving way to the river of ice behind it.
Something similar happened in the 1990s and early 2000s to glaciers in the Antarctic Peninsula — the tail-shaped part of the continent that extends toward South America. There, warm temperatures caused the catastrophic breakup of ice shelves over the course of just a few years. Two decades later, the peninsula’s glaciers are still flowing at two or three times their previous rate, contributing to sea level rise.
Pine Island and other West Antarctic glaciers are much bigger than the ones that flow out of the Antarctic Peninsula, she noted, making the consequences of retreat far more extreme.
“Ice loss here could be catastrophic and irreversible on centennial time scales,” Davies said.
Joughin’s models can’t say what will happen next. He and his colleagues haven’t observed melt ponds forming on the surface of the ice shelf — something that is known to make ice less stable. The rifting of the ice appeared to slow down in 2020.
But if ice shelves can shift quickly and decisively, so too can humanity. Healing the ozone hole and taking swift action against climate change will alter the conditions in Antarctica’s atmosphere and oceans and help stabilize the continent’s glaciers.
“The future is still open to change,” Davies said — if people do what is needed to change it.