One of Antarctica’s most important glaciers could continue contributing to sea-level rise even if ocean-driven melting beneath its floating ice shelf were dramatically reduced, according to new research published in Geophysical Research Letters.
Thwaites Glacier in West Antarctica currently accounts for about 4% of global sea-level rise – a rate that has trebled since the mid-1990s.
The new findings suggest that the ongoing retreat of Thwaites is being driven not only by present-day ocean conditions, but also by the glacier’s response to past environmental changes.
Researchers from the British Antarctic Survey and collaborating institutions used three independent ice-sheet models to test an extreme scenario: removing all melting beneath the floating ice shelves of Pine Island Glacier and Thwaites Glacier for 150 years. While such conditions are unrealistic in the real world, the experiment provides a powerful way to separate the effects of current ocean warming from the glaciers’ longer-term responses to historical change.
The results revealed a striking contrast between the two neighbouring glaciers. Pine Island Glacier quickly thickened and advanced towards the submarine ridge from which it retreated in the mid-twentieth century. In contrast, Thwaites Glacier continued to lose ice in every model simulation, although the rate of loss gradually declined over time.
The study found little evidence that Thwaites would regain its former extent, even under this highly favourable no-melt scenario. Modelling showed that the glacier’s grounding line remained largely retreated, indicating that the glacier has entered a substantially different state from that which existed before its retreat began in the 1940s and 1950s.
Scientists conclude that a significant component of Thwaites’ current ice loss is an ongoing response to historical climate and ocean changes that occurred decades ago. As a result, cooling the ocean alone is unlikely to restore the glacier to its previous condition on timescales relevant to human societies.
The findings do not mean that rapid future collapse is inevitable. Under the zero-melt experiments, the rate of ice loss slowed rather than accelerated. However, the research suggests that some future contribution to sea-level rise from Thwaites is already unavoidable, reinforcing the need for both greenhouse gas mitigation and adaptation planning for rising seas.