Why is the Thwaites Glacier referred to as the 'Doomsday Glacier'?

Important Highlights

It’s rare to see a TV comedian dive into glaciology, but that’s exactly what CBS's Stephen Colbert did on September 8, 2022. He included new research in the opening monologue of his primetime show, "Late Night with Stephen Colbert."

The segment was inspired by an Antarctic glacier that has been rapidly disintegrating. The media has dubbed it the "Doomsday Glacier," which gave Colbert plenty of material for his comedic jabs.

"Couldn’t we go for something a bit more upbeat like the 'free guac glacier' or the 'have you lost weight iceberg?'" Colbert joked.

What Exactly is the Thwaites Glacier?

Technically speaking, the glacier in question is named the Thwaites Glacier. As Colbert later pointed out, "Doomsday Glacier" is merely a nickname — one that has faced criticism from some scientists.

The Thwaites Glacier, named after geologist Fredrik T. Thwaites, is retreating, losing ice mass and thinning out. This is a growing global issue, as glaciers around the world, from Scandinavia to the Himalayas, are undergoing similar changes.

Like many glaciers, the Thwaites Glacier drains directly into the ocean, which contributes to the rising sea levels as it continues to melt.

"Thwaites currently loses around 50 billion tons (more than 45 billion metric tons) of ice every year, which is more than what is replaced by new snowfall. This rate has increased several times over the past three decades," explains Robert Larter, a marine geophysicist at the British Antarctic Survey, in an email.

The water from the melted ice has to go somewhere. Global sea levels rise by over 0.11 inches (3 millimeters) annually. Experts estimate that the Thwaites Glacier alone accounts for 4 percent of this rise in water. "The ice loss rate is expected to continue growing, but the speed at which it will increase is a key focus of ongoing research," says Larter.

How Do Glaciers and Ice Sheets Differ?

Antarctica is an exceptionally harsh environment by human standards. Around 97.6 percent of the continent is covered by the vast Antarctic Ice Sheet, an immense expanse of frozen water.

According to Larter, an ice sheet, or continental glacier, is defined as "a very large body of ice" that spans over 19,000 square miles (50,000 square kilometers). The Antarctic Ice Sheet more than qualifies, as it stretches across nearly 5.4 million square miles (14 million square kilometers), making it about the size of Mexico and the contiguous United States combined.

For convenience, the enormous ice sheet has been divided into regions. One of these is the West Antarctic Ice Sheet (WAIS), home to the Thwaites Glacier.

"A glacier is a body of ice that moves along a valley or within an ice sheet," explains Larter. He adds that when this happens within an ice sheet, it is more accurately referred to as an 'ice stream.'

An ice sheet can contain multiple glaciers and/or ice streams, though defining the exact boundaries between them is not always straightforward.

"The usual method is that sections of the ice sheet which flow towards a single outlet are generally regarded as an ice stream or glacier. This concept is similar to watersheds or river basins on land," explains Frank Nitsche, a geophysicist at Columbia University, in an email. "The areas of the ice sheet where the ice flows toward one specific outlet are considered part of that particular glacier."

Where Sea Meets Ice Shelf

The Thwaites Glacier, along with ice and meltwater, naturally flows into the Amundsen Sea. Many other glaciers empty into this same body of water, but the Thwaites stands out due to its extraordinary size.

Spanning around 80 miles (120 kilometers) wide, the Thwaites is the largest glacier on Earth. "It covers an area of 74,000 square miles (193,000 square kilometers), which is slightly larger than the state of Florida, yet a bit smaller than the island of Great Britain," says Larter.

Nitsche and Larter were among the co-authors of a groundbreaking 2022 Thwaites Glacier study, published in the journal Nature Geoscience, which made headlines worldwide and even inspired some Colbert jokes in September.

The researchers deployed an autonomous underwater vehicle (AUV) into the depths of the Amundsen Sea. Equipped with geophysical sensors, it surveyed the region where the Thwaites Glacier meets the seabed.

A significant part of the glacier, known as the ice shelf, extends over the sea. "Ice shelves are delicate and highly susceptible to both surface and basal melting. The remaining ice shelf of the Thwaites Glacier is expected to disintegrate within the coming decades," states Larter.

This is far from reassuring. Ice shelves function as cold buttresses, slowing the overall flow of the glacier. If the Thwaites Glacier loses its 'buttress,' the glacier may start to lose ice at an even faster rate than it currently does.

Recently, scientists have discovered signs of rapid retreat in the Thwaites' more recent history, which may offer insights into its future behavior.

The Speed of Glacial Retreat

The Thwaites ice shelf slopes downward at an angle, eventually reaching the ocean floor. The point where a glacier detaches from the seabed is known as the grounding zone.

In 2022, the research team used their AUV to document a series of ridges etched into the sediment at the Amundsen Sea's bottom. Each ridge marks the previous location of the Thwaites grounding zone, offering a timeline of the glacier's retreat.

Recently, the rate of melting has significantly increased, signaling a change in the glacier's behavior.

Earlier studies indicated that between 2011 and 2017, the Thwaites Glacier's grounding zone receded at a rate of 0.37 to 0.5 miles per year (0.6 to 0.8 kilometers per year).

By analyzing the spacing between the ridges, Nitsche, Larter, and their team found that, within the last two centuries, there was a remarkable five-and-a-half-month period when the grounding zone retreated at an accelerated pace of 1.4 miles (2.3 kilometers) per year.

Prior to the new study, no one had realized the glacier could have flowed or lost ice at such a rapid pace. Could this occur again in the future? Unfortunately, the answer is "yes."

"The grounding zone is likely to shift off stabilizing high points on the ocean floor, triggering similar rapid retreat events in the near future," stated the authors in the Nature Geoscience study.

Is the Thwaites Really a "Doomsday" Glacier?

The future of the Thwaites Glacier could have major consequences for the planet.

Currently, the glacier sits in a deep ocean basin. If it retreats significantly, Nitsche warns, "ocean water will enter that basin, and surrounding ice, including other glaciers, will begin flowing into it and thinning as well."

As Nitsche points out, the melting process would take centuries — perhaps even over a thousand years — to fully unfold. However, this shouldn't be a reason for complacency, especially considering that the loss of the Thwaites could also lead to the disappearance of a large portion of the West Antarctic Ice Sheet.

"If the Thwaites Glacier completely disappears, global mean sea level will rise by 25.6 inches [65 centimeters]," Larter explains. He adds that if "all the adjacent sections of the West Antarctic Ice Sheet, where the ice bed lies below sea level, are lost," the global mean sea level could increase by nearly 11 feet (3.3 meters).

Even so, perhaps the Thwaites doesn't quite live up to its 'doomsday glacier' label.

"I don't care for the term 'doomsday glacier,'" Nitsche says. He feels that the word 'doomsday' suggests we are powerless to take any preventative measures to slow the glacier's retreat.

In fact, there is something we can do. By cutting down our greenhouse gas emissions, we can help slow the Thwaites' retreat — at least for a while.

"It will take centuries to melt all the ice in the Thwaites Glacier, but this process will accelerate if we keep warming the planet rapidly, and it will slow down if we manage to significantly reduce global warming," Nitsche points out. "We may be able to influence the speed of this process and the time we have to adjust or mitigate its impacts."