The world’s largest glacier is melting much faster and could add twice as much to global sea levels as previously expected over the next century.

New research published this week by a team of glaciologists has found that the Thwaites glacier in West Antarctica is losing mass rapidly because warm seawater is pushing underneath it and melting its core. This could add 1.2 inches (30mm) to water levels even if global warming does not accelerate as predicted.

The findings, published in the journal Nature Communications, add to a growing body of evidence that shows that the glacier, which has been receding for decades, is now losing mass even faster than scientists thought.

Researchers at the University of California in the United States collaborated with NASA’s Jet Propulsion Laboratory for the study. Here’s what we know about the findings: What is Thwaites and why is it important?

Nicknamed the “Doomsday Glacier”, Thwaites is the largest glacier on Earth, spanning an area of around 192,000sq km (74,130sq miles) or roughly the size of Senegal – and larger than the US state of Florida.

It is located on the Walgreen Coast of Marie Byrd Land in remote western Antarctica and forms part of the great 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, although he never visited it.

In the 1980s, scientists discovered that Thwaites is melting rapidly and have closely monitored its melting process as concerns have grown ever since.

Because it is so big, the glacier’s collapse would sharply raise global sea levels by a catastrophic amount – although researchers don’t project that will happen for many decades, or even a few centuries.

Together, Thwaites and other glaciers such as the Pine Island glacier – an ice stream in West Antarctica which flows into Pine Island Bay in the Amundsen Sea – act as a barrier that holds back the vast and vulnerable West Antarctic ice sheet. If melted, the ice sheet could cause many coastal cities to be submerged around the world.

At present, ice loss from Thwaites contributes 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 continues to lose 50 billion tonnes of ice per year. Why is the glacier melting?

The main drivers are warm ocean water which is actively melting the Thwaites glacier from underneath it, according to several studies.

Ocean warming is caused by human-induced climate change, in particular from the burning of polluting fossil fuels.

In a 2019 study, the NASA Jet Propulsion Laboratory discovered a giant underwater cavity beneath the Thwaites glacier that spread across an area two-thirds the size of Manhattan, which researchers said was likely speeding up the glacier’s thinning.

Rising temperatures have caused glaciers to lose about five percent of their ice since 2000, according to the European Space Agency. What has the latest research found?

Thwaites could add as much as 1.2 inches (30mm) – double the current estimates – to sea levels by 2100, even without any additional global warming, the study found.

The researchers said they used new computer models that paint a clearer picture of melting activity under the threatened glacier at its grounding line – the boundary where it transitions from resting entirely on bedrock to spreading out over the sea in the form of ice shelves.

Where other ice sheet models conclude a grounding line is fixed, the scientists said they developed the concept of a broader “grounding zone” instead. In this scenario, seawater lifts and lowers the ice in a “tidal pumping” process that allows warm water to reach “deep underneath the ice sheets and causing vigorous melting,” lead author Mattia Poinelli, a project scientist at UCLA, told media.

That melting process is accelerating the Thwaites’ “unpinning” from the Mouginot Ridge – an important underwater bedrock currently stabilising the glacier from below. The study concluded that there is a 60 percent chance that Thwaites could unpin from the ridge by the end of the century.

However, experts say more studies are needed to accurately predict the volume of Thwaites’ ice loss.

In separate findings, scientists from the British Antarctic Survey concluded that Thwaites will continue losing ice for at least the next 150 years, even under the most extreme ocean cooling conditions imaginable.

The study, which used computer simulation models that examined the melting effects of the ocean over the next century and a half, was published in Geophysical Research Letters in July.