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‘We’re not doomed!’ UN’s ‘Doomsday’ climate models deemed ‘extreme’ and ‘unlikely’, new study finds

August 22, 2024 | | Print Article

A new Dartmouth-led study has found that the United Nation’s “worst case scenario” for Antarctica’s melting glaciers is incorrect.

The U.N.’s Intergovernmental Panel on Climate Change (IPCC) has previously predicted that the melting “Doomsday” glaciers could drastically raise global sea levels, thus eradicating a number of coastline communities across the planet.

“Released in full last year, the IPCC’s sixth assessment report introduced a possible scenario in which the collapse of the southern continent’s ice sheets would make Antarctica’s contribution to average global sea level twice as high by 2100 than other models project—and three times as high by 2300,” according to Dartmouth.

But according to three new models, the U.N.’s “Doomsday” model is “extreme” and “unlikely,” and the glaciers aren’t apt to break apart quite as fast and furiously as previously expected.

“We’re not reporting that the Antarctic is safe and that sea-level rise isn’t going to continue—all of our projections show a rapid retreat of the ice sheet,” study co-author Mathieu Morlighem said.

“But high-end projections are important for coastal planning, and we want them to be accurate in terms of physics. In this case, we know this extreme projection is unlikely over the course of the 21st century,” he added.

According to Dartmouth, the IPCC’s prediction is based on a “hypothetical mechanism of how ice sheets—the thick, land-based glaciers covering polar regions—retreat and break apart.”

“The mechanism, known as the Marine Ice Cliff Instability [MICI], has not been observed and has so far only been tested with a single low-resolution model,” Dartmouth notes.

Morlighem and his crew tested MICI “with three high-resolution models and an improved rate of ice collapse that more accurately capture the complex dynamics of ice sheets.”

They specifically simulated the retreat of Antarctica’s Thwaites Glacier, a 75-mile-wide ice sheet known as the “Doomsday Glacier” because of how high it could potentially raise sea levels were it to melt.

“Their models showed that even the imperiled Thwaites is unlikely to rapidly collapse during the 21st century as MICI would predict,” Dartmouth notes.

Morlighem has said that these findings suggest that the underlying physics of the IPCC’s projection is inaccurate.

According to Dartmouth, “The idea behind MICI is that if an ice shelf—the floating extension of the land-based ice sheet—collapses rapidly, it would potentially leave the ice cliffs that form the outer edge of the ice sheet exposed and unsupported.”

If tall enough, these cliffs would collapse under their own weight, thus exposing even taller cliffs and leading to the glacier rapidly “retreating” toward the mainland continents.

“The loss of this ice into the ocean where it would melt is what would lead to the projected dramatic sea-level rise,” Dartmouth notes.

However, Morlighem and his crew found that the collapse process wouldn’t be this simple or fast.

“Everyone agrees that cliff failure is real—a cliff will collapse if it’s too tall,” he said. “The question is how fast that will happen. We found that the rate of retreat is nowhere near as high as what was assumed in these initial simulations. When we use a rate that is better constrained by physics, we see that ice cliff instability never kicks in.”

They focused specifically on the “Doomsday Glacier” because it’s been reported to be especially vulnerable to collapse.

“The researchers used a computer model based on the physics of how ice melts and moves to simulate Thwaites’ retreat for 100 years following a sudden hypothetical collapse of its ice shelf, as well as for 50 years under the rate of retreat actually underway,” Dartmouth reports.

In their simulations, the “Doomsday Glacier” didn’t retreat inland at the speed previously predicted.

“Instead, without the ice shelf holding the ice sheet back, the movement of the glacier toward the ocean accelerates rapidly, causing the ice sheet to expand away from the interior. This accelerated movement also thins the ice at the glacier’s edge, which reduces the height of the ice cliffs and their susceptibility to collapse,” according to Dartmouth.

Vivek Saxena
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