PREVIEW

The Antarctic glacier that is the polar continent’s single largest contributor to sea-level rise has accelerated sharply since 2017.

The Pine Island glacier forms a crucial part of the West Antarctic ice sheet, which contains enough ice to raise global sea levels by around 5.3 metres if it were to melt completely.

Pine Island, the fastest-flowing glacier on the continent, is now moving at close to 5km (3 miles) a year, according to a new paper.
Its authors fear the rapid speed-up suggests the floating ice shelf in front of the glacier is no longer providing the support needed to hold the inland ice in place.

Along with the Thwaites Glacier, dubbed the Doomsday Glacier due to the potential consequences were it to melt, Pine Island forms a crucial part of the West Antarctic ice sheet, which contains enough ice to raise global sea levels by around 5.3 metres if it were to melt completely.

The glacier flows into the Pine Island ice shelf, which extends over the ocean and has long been thought to act as a buttress, slowing the movement of ice from inland and protecting it from warmer seawater. Researchers estimate the shelf has been holding back ice equivalent to around 51 centimetres of global sea-level rise.

In the latest study, Sarah Wells-Moran of the University of Chicago and her colleagues analysed satellite images from the Copernicus Sentinel-1 mission, alongside observations dating back to the early 1970s.

“Using observed time-series of the surface velocity fields between 2015 and 2024, we show multiple episodes of acceleration in ice flow and a marked reduction in the buttressing stresses,” Wells-Moran and her colleagues write in their paper. “These observations show that PIIS (Pine Island Ice Shelf)experienced an near-total loss of its buttressing capacity during the observational record.”

They found that Pine Island glacier’s speed increased from about 2.2km a year in 1974 to 4km a year by 2008. Between 2017 and 2023, it accelerated further to nearly 5km a year — a rise of around 20% in just six years and more than a doubling since the early 1970s.

Over the four decades from 1973 to 2013, the rate at which ice was discharged from the glacier increased by more than 75%.

These changes have been accompanied by a dramatic retreat of the glacier’s grounding line — the point where the ice begins to float rather than rest on the seabed — by more than 30km.
By comparing the observations with computer models, the researchers concluded that the acceleration is being driven by thinning and fracturing of the ice shelf as warmer ocean water penetrates further beneath it. The margins of the shelf have become detached from the surrounding ice, effectively “unzipping” its sides.
As a result, the team says the Pine Island ice shelf now provides “negligible buttressing” to the glacier upstream, allowing ice to flow more freely into the ocean and accelerating ice loss from West Antarctica.

The scientists fear that accelerated ice loss in the region could have major impacts on the world’s coastlines over the coming decades.