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The world’s widest glacier – Thwaites glacier in Antarctica – is already collapsing at an alarming rate due to ocean warming, with worrying implications for global sea-level rise. Now, a new study shows that it will continue to lose ice for at least the next 150 years, even under the impossible scenario of extremely cool oceans.
This means that future ice loss from the glacier is unavoidable, even under the most optimistic climate mitigation scenarios.
Dubbed the “doomsday glacier”, this vast mass of ice is roughly the size of Great Britain. Together with the neighbouring Pine Island glacier, it’s the area of Antarctica losing the most ice, mainly due to melting by the warmer ocean waters.
“The Pine Island and Thwaites glaciers are the biggest contributors to sea-level rise in Antarctica at the moment, and they’re losing ice at an increasing rate,” says Rosie Williams at the British Antarctic Survey.
If Thwaites glacier collapses completely, it is expected to trigger a more widespread loss of the ice sheet covering West Antarctica, causing a calamitous sea-level rise of 5 metres. So determining how it behaves in future is crucial.
To explore this, Williams and her colleagues “did something quite wild”, she says. In three different computer models of the ice sheet, they turned off all ocean-driven melting – an impossible condition in reality, even under the most extreme ocean cooling scenarios – and watched what would happen over the next 150 years. The aim was to see the future trajectory of Thwaites glacier and Pine Island glacier, even without warming oceans.
Surprisingly, the glaciers followed opposite paths. Pine Island glacier re-advanced and became more stable. “But with Thwaites glacier, we found something really different,” says Williams. Over the entire 150 years of the simulations, the glacier continued to lose ice, even though the rate of loss slowed over time. “Our general expectation was… if you turned off that ocean melting, the ice would be able to thicken and re-advance. It’s somewhat of a surprise that Thwaites glacier can’t do that.”
The researchers think that Thwaites is still being affected by extreme El Niño conditions in the 1940s which destabilised Antarctica’s glaciers and kick-started their retreat. “We’re still seeing some effect of that playing out today with Thwaites. [Glaciers] are really slow-moving. They have a long memory,” she says.
On top of this, human-induced climate change has probably accelerated the melt, says Ted Scambos at the University of Colorado Boulder. “Ocean heat delivered to the base of the ice … over the past four decades or so, as a result of anthropogenic warming, has pushed the Thwaites system into an inherently unstable configuration,” he says.
But despite future ice loss being locked in, this doesn’t mean that strategies to reduce climate change and ocean warming are futile. “Almost the opposite,” says Williams. “Under the zero-melt scenario, [Thwaites glacier] still loses ice, but the more warming you have in the ocean, the faster that ice is lost, so it’s still really essential to bring down our emissions and control that rate of ice loss.”
“Every fraction of a degree really matters for trying to preserve these glaciers into the future, which matters for all of us, in terms of sea-level rise globally,” says Williams.
The temperature of the ocean adjacent to Thwaites glacier is projected to rise at triple the historical rate throughout the 21st century, leading to increased ice melting. The big worry is that this may trigger a doomsday scenario of run-away collapse of Thwaites glacier that, in turn, would trigger the collapse of the whole of the West Antarctic ice sheet in a process called marine ice sheet instability.
Here, the study by Williams and her colleagues offers slight hope. “We haven’t crossed the point of no return,” says Mathieu Morlighem at Dartmouth College, New Hampshire. “In the best-case scenario…if melt from the ocean stops, Thwaites doesn’t… lead to a collapse of the West Antarctic ice sheet.”
The big question for the future is what happens with realistic ocean temperatures, says Williams, who is now working on this.
Meanwhile, another study published this week revealed other worrying news about Thwaites glacier. A more precise model of how the glacier interacts with the ocean indicates that it might retreat more rapidly than previously thought, potentially contributing to double the sea-level rise previously projected.
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