New research has found that Antarctica's Thwaites glacier is losing ice more quickly than earlier models suggested, and could raise global sea levels by twice the amount previously projected over the next hundred years. The study, published this week in the journal Nature Communications, was carried out by glaciologists at the University of California working alongside NASA's Jet Propulsion Laboratory. According to Al Jazeera, the findings indicate the glacier could add 1.2 inches (30mm) to sea levels by 2100 even if global warming does not speed up beyond current forecasts.
Why it matters
Thwaites is the biggest glacier on Earth, covering roughly 192,000 square kilometres — an area Al Jazeera compares to the size of Senegal, and larger than the US state of Florida. It sits on the Walgreen Coast of Marie Byrd Land in western Antarctica and is part of the wider West Antarctic ice sheet, which is 14 times its size.
Because of its scale, the glacier plays an outsized role in how much the world's coastlines will change. Thwaites and neighbouring glaciers such as Pine Island act as a barrier that holds back the West Antarctic ice sheet. Should that larger sheet melt, many coastal cities around the world could be flooded. At present, ice loss from Thwaites accounts for about four percent of global sea-level rise, according to Al Jazeera.
The glacier has shed more than 1,000 billion tonnes of ice since 2000 and is still losing around 50 billion tonnes each year. It was first charted in 1947 and takes its name from Fredrik T Thwaites, an American glaciologist who died without ever seeing it. Scientists noticed in the 1980s that it was melting quickly and have watched it closely since.
Warm water is melting the glacier from beneath
The study points to warm ocean water as the main cause, with seawater working its way under the ice and melting it from below. That ocean warming is driven by human-induced climate change, particularly the burning of fossil fuels. Al Jazeera notes that a 2019 NASA Jet Propulsion Laboratory study found a large underwater cavity beneath the glacier, covering an area about two-thirds the size of Manhattan, which researchers said was probably accelerating its thinning.
The new work focuses on the grounding line — the point where the glacier stops resting on bedrock and begins to float out over the sea as an ice shelf. Where earlier ice-sheet models treated that line as fixed, the researchers introduced the idea of a wider "grounding zone." Within that zone, seawater lifts and lowers the ice in a process described as tidal pumping, which lets warm water reach far beneath the ice and melt it vigorously, lead author Mattia Poinelli, a project scientist at UCLA, told media.
That melting is speeding up the glacier's detachment from the Mouginot Ridge, an underwater bedrock feature that currently helps hold it in place from below. The study puts the chance of Thwaites coming loose from the ridge by the end of the century at 60 percent.
The authors acknowledge that more research is needed before the volume of ice the glacier will lose can be predicted with confidence. Separately, scientists at the British Antarctic Survey concluded that Thwaites will keep shedding ice for at least another 150 years, even under the most extreme ocean cooling they could model. That study appeared in Geophysical Research Letters in July.
The picture fits a broader trend. The European Space Agency has reported that rising temperatures have cost the world's glaciers about five percent of their ice since 2000.
What to watch
The coming years will show whether Thwaites begins to pull away from the Mouginot Ridge, the event the new study gives a 60 percent chance of occurring this century. Further modelling and field studies are expected to sharpen estimates of how much ice the glacier will ultimately release.
