Climate change: Assessing West Antarctic glacier melting

Insights into the factors that might influence the potential collapse of the Thwaites Glacier, which could increase global sea levels by over half a metre, are reported in two papers published in Nature. The findings uncover varied patterns of melting and suggest that complex ice–ocean interactions will play a key role in the future of this glacier.

Ice loss from the Thwaites Glacier, part of the West Antarctic Ice Sheet, has the potential to cause rapid sea-level rise over the coming century. Its complete collapse is projected to increase the global sea- level by about 65 cm. This collapse could also destabilize neighbouring glaciers, potentially increasing future sea level by an additional three metres. The Thwaites Glacier lies on bedrock that slopes downwards towards the coast, making it particularly vulnerable to instabilities that could lead to rapid and irreversible ice loss. Ocean conditions, ice thinning and flow rates are known to influence the retreat of the glacier’s grounding line, where it detaches from the ground and starts floating, but exactly how these factors operate remains poorly understood.

To investigate the vulnerability of the Thwaites Glacier to collapse, two groups report observations of ice melt rates and the properties of the glacier and surrounding ocean. These measurements were taken via an access hole drilled through approximately 587 m of ice about 1.5–2.0 km downstream of the grounding line. Peter Davis and colleagues used a fixed- positioned device, 1.5 m under the ice shelf, to measure ocean temperature, salinity, velocity, and the melt rate over time. They found warm water beneath the floating ice shelf, and that stratification separate these waters from the ice, thereby suppressing melting. These findings show that rapid retreat of the Thwaites Glacier can occur without extensive basal melting. Britney Schmidt and colleagues used an underwater vehicle to measure the same ocean properties, plus the ice shape over a wider region. They found that high melt rates occur where ice is sharply sloped at the ocean interface, whereas melting was suppressed at flat interfaces. These observations demonstrate the influence of ice morphology on ice loss.

The findings improve our understanding of the present state of an important West Antarctic glacier and highlight key challenges for future climate modelling.