Science & Nature

Why Is the Thwaites Glacier Called the ‘Doomsday Glacier’?

Why Is the Thwaites Glacier Called the 'Doomsday Glacier'? thumbnail

Thwaite's glacier
The Thwaites Glacier, part of the the West Antarctic Ice Sheet, or WAIS, is the widest glacier on Earth, at 80 miles (120 kilometers) wide. Felton Davis/Flicker

It’s not often that a TV comedian talks glaciology. But CBS funnyman Stephen Colbert did just that Sept. 8, 2022, when he worked some new research into the opening monologue on his primetime series, “Late Night with Stephen Colbert.”

The bit was inspired by an Antarctic glacier that’s disintegrated to an alarming degree. Headline writers have taken to calling it the “Doomsday Glacier,” which prompted the barrage of jokes from Colbert.

“Can’t we pick something a little happier like the ‘free guac glacier’ or the ‘have you lost weight iceberg?'”asked Colbert.

What Is the Thwaites Glacier?

Technically, the glacier in question is called the Thwaites Glacier. As Colbert later acknowledged, “Doomsday Glacier” is just a nickname — one that’s been criticized by a number of scientists.

Named after geologist Fredrik T. Thwaites, the Thwaites Glacier is on the retreat; it’s thinning out and losing ice mass. That’s a common story these days — glacial retreat is a worldwide problem, affecting communities from Scandinavia to the Himalayas.

And like a lot of other glaciers, the Thwaites feeds directly into the ocean, contributing to the rise in sea levels as it melts.

“Thwaites currently loses about 50 billion tons [over 45 billion metric tons] … more ice each year than is replaced by new snowfall, and this rate of loss has increased several fold over the past 30 years,” says Robert Larter, a marine geophysicist at the British Antarctic Survey, in an email.

All the water from the melted ice has to go somewhere. The global sea level currently rises by over 0.11 inches (3 millimeters) per year. Experts calculate that the Thwaites Glacier alone supplies 4 percent of this incoming water. “The rate of ice loss is expected to continue to increase, but determining how rapidly it will increase is the objective of current research,” Larter says.

What’s the Difference Between a Glacier and an Ice Sheet

By human standards, Antarctica is a singularly harsh environment. About 97.6 percent of the continent is covered by an enormous blanket of frozen water, the famed Antarctic Ice Sheet.

According to Larter, an ice sheet, or continental glacier, is “a very large body of ice” that is greater than 19,000 square miles, or 50,000 square kilometers. The Antarctic Ice Sheet more than fits the bill; with an area of nearly 5.4 million square miles (14 million square kilometers), it’s around the size of Mexico and the contiguous United States put together.

Conveniently, the giant ice sheet has been split up into regions. One of these is the West Antarctic Ice Sheet, or the WAIS, where the Thwaites Glacier resides.

“A glacier is a body of ice that flows along a valley or within an ice sheet,” says Larter, who adds that “in the latter case, it is more properly called an ‘ice stream.'”

One ice sheet may contain several glaciers and/or ice streams — but it’s not always easy to define the boundaries between these.

“The common approach is that parts of the ice sheet that are moving toward one outlet point are usually considered an ice stream or glacier. This can be compared to watersheds or river basins on land,” explains Columbia University geophysicist Frank Nitsche, in an email. “The parts of the ice sheet where the ice is flowing toward one outlet point is considered part of that [individual] glacier.”

Where Sea and Ice Shelf Meet

Ice and meltwater from the Thwaites naturally flow into the Amundsen Sea. Many other glaciers pour themselves out into the same body of water, but one thing that sets the Thwaites apart is its unusual girth.

At about 80 miles (120 kilometers) across, this is the widest glacier on the planet. “It covers an area of 74,000 square miles [193,000 square kilometers], which is a little larger than the state of Florida and a little smaller than the island of Great Britain,” says Larter.

Nitsche and Larter were among the co-authors of a 2022 Thwaites Glacier study, published in the journal Nature Geoscience, that made international news (and prompted those Colbert jokes) this September.

The authors sent an autonomous underwater vehicle, AUV, into the depths of the Amundsen Sea. Using geophysical sensors, it checked out the area where the Thwaites meets the seabed.

A large portion of the glacier, known as its ice shelf, jets out over the sea. “Ice shelves are very fragile and vulnerable to surface and basal melting. The Thwaites Glacier’s remaining ice shelf is expected to break up within the next couple of decades,” notes Larter.

That’s not a comforting thought. Ice shelves act like frigid buttresses, slowing down the flow of the glacier as a whole. So if the Thwaites loses its “buttress,” the glacier could begin to shed its ice even more rapidly than it already does.

And now, scientists have found evidence of a fast-paced retreat in the Thwaites’ modern history that may tell us something about its future.

The Rate of Glacial Retreat

The underside of the Thwaites ice shelf plunges downward at an angle until it reaches the ocean floor. Scientists have a name for the point where an ocean-bordering glacier disconnects from the seabed: the grounding zone.

Using their AUV, the 2022 research team documented a series of ridges that had been carved into the sediment at the bottom of the Amundsen Sea. Each imprint marks the spot where the Thwaites grounding zone used to be; taken together, they record the glacier’s overall decline.

Apparently, not too long ago, the melting trend kicked into high gear.

Earlier research showed that the Thwaites Glacier’s grounding zone moved backwards at a rate of 0.37 to 0.5 miles per year (0.6 to 0.8 kilometers per year) between 2011 and 2017.

Yet by measuring the distance between the ridges, Nitsche, Larter and their colleagues discovered that — at some point within the past 200 years — there was an unusual five-and-a-half-month period when the Thwaites grounding zone pulled back at the accelerated speed of 1.4 miles (2.3 kilometers) per year.

Before the new study, no one realized the glacier had ever flowed — or lost ice — that quickly. Could it happen again someday? The answer is an unfortunate “yes.”

“Similar rapid retreat pulses are likely to occur in the near future when the grounding zone migrates back off stabilizing high points on the ocean floor,” wrote the authors in the Nature Geoscience study.

Is the Thwaites Really a “Doomsday” Glacier?

The fate of the Thwaites could have serious repercussions for our planet.

Today, the glacier occupies a deep ocean basin. If it retreats “substantially,” Nitsche cautions that “ocean water would enter that basin. The surrounding ice including other glaciers would start flowing into this basin and start thinning as well.”

Granted, as Nitsche explains, the melting process would take hundreds of years “if not more than a thousand” to unfold. But that’s no excuse for inaction on our part — especially because the loss of the Thwaites might also cost us a huge percentage of the West Antarctic Ice Sheet.

“If the Thwaites Glacier is lost entirely this will cause global mean sea level to rise by 25.6 inches [65 centimeters],” Larter tells us. He also says that if “all the adjoining parts of the West Antarctic Ice Sheet where the ice bed is below sea level are lost,” there’ll be a global mean sea level increase of nearly 11 feet, or 3.3 meters.

Even so, maybe the Thwaites doesn’t deserve its apocalyptic nickname.

“I don’t like the term ‘doomsday glacier,'” says Nitsche. In his view, the word “doomsday” implies that we can’t take any proactive steps to slow the glacier’s retreat.

Actually, we can. Reducing our greenhouse gas emissions could go a long way toward preserving the Thwaites — for a while, at least.

“It will take a lot of time (hundreds of years) to melt all the ice of Thwaites Glacier, but it will happen faster if we continue to heat up the planet quickly and much slower if we managed to drastically limit the warming of the planet,” Nitsche observes. “So we might have some influence on how quickly this would happen and how much time we have to adapt or mitigate potential effects.”

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