The world’s largest glacier is melting much faster than previously thought, and could add roughly twice as much to global sea levels over the next century as earlier estimates suggested. The finding comes from new research published this week by a team of glaciologists, which focused on the Thwaites glacier in West Antarctica.
According to the study, the glacier is losing mass rapidly because warm seawater is flowing underneath it and melting its core. The researchers said this process could add 1.2 inches (30mm) to water levels even if global warming does not accelerate as predicted. The findings were published in the journal Nature Communications, and the work was a collaboration between researchers at the University of California and NASA’s Jet Propulsion Laboratory.
Why the Doomsday Glacier matters for sea levels
Nicknamed the “Doomsday Glacier”, Thwaites covers an area of around 192,000 square kilometres (74,130 square miles). That is roughly the size of Senegal and larger than the US state of Florida. It sits on the Walgreen Coast of Marie Byrd Land in remote western Antarctica and forms part of the West Antarctic ice sheet, which includes other glaciers and is 14 times the size of Thwaites.
The glacier was first mapped in 1947 and is named after the late American glaciologist Fredrik T Thwaites, who never visited it. Scientists first found in the 1980s that Thwaites was melting rapidly, and they have monitored the process closely ever since as concern has grown.
Because of its size, a collapse of the glacier would sharply raise global sea levels by a catastrophic amount. Researchers, however, do not expect that to happen for many decades, or even a few centuries. Thwaites and the Pine Island glacier, which flows into Pine Island Bay in the Amundsen Sea, together hold back the vast and vulnerable West Antarctic ice sheet. If that ice sheet melted, many coastal cities around the world could be submerged.
Warm ocean water driving ice loss at Thwaites
Ice loss from Thwaites currently accounts for around four percent of all global sea-level rise. Studies have calculated that the glacier has lost more than 1,000 billion tonnes of ice since 2000, and that it continues to lose about 50 billion tonnes each year.
Several studies identify warm ocean water as the main driver, actively melting the glacier from below. Ocean warming, in turn, is linked to human-induced climate change, particularly the burning of polluting fossil fuels. A 2019 study by the NASA Jet Propulsion Laboratory found a giant underwater cavity beneath Thwaites, covering an area about two-thirds the size of Manhattan. Researchers said it was likely speeding up the glacier’s thinning.
The European Space Agency has said rising temperatures have caused glaciers to lose about five percent of their ice since 2000. The new study found that Thwaites could add as much as 1.2 inches (30mm) to sea levels by 2100, double the current estimates, even without any further global warming.
New models point to tidal pumping and possible unpinning
The researchers said they used new computer models to get a clearer picture of melting beneath the glacier at its grounding line, the boundary where it stops resting entirely on bedrock and begins spreading over the sea as ice shelves. While other ice sheet models treat the grounding line as fixed, the scientists developed the idea of a broader “grounding zone” instead.
In this model, seawater raises and lowers the ice in a “tidal pumping” process. Lead author Mattia Poinelli, a project scientist at UCLA, told media that this allows warm water to reach “deep underneath the ice sheets and causing vigorous melting.”
The study said this melting is speeding up the glacier’s “unpinning” from the Mouginot Ridge, an underwater bedrock feature that currently stabilises Thwaites from below. According to the study, there is a 60 percent chance that the glacier could unpin from the ridge by the end of the century. Experts say more studies are needed to predict accurately how much ice Thwaites will lose.
Separately, scientists from the British Antarctic Survey concluded that Thwaites will keep losing ice for at least the next 150 years, even under the most extreme ocean cooling conditions imaginable. That study used computer simulations of ocean melting over the next century and a half and was published in Geophysical Research Letters in July.
