Glacier's retreat is now irreversible

13 January 2014 by Harriet Jarlett

Pine Island Glacier, the largest single contributor to sea-level rise in Antarctica, has started shrinking, say scientists.

The work, published in Nature Climate Change, shows the glacier's retreat may have begun an irreversible process that could see the amount of water it is adding to the ocean increase five-fold.

"At the Pine Island Glacier we have seen that not only is more ice flowing from the glacier into the ocean, but it's also flowing faster across the grounding line - the boundary between the grounded ice and the floating ice. We also can see this boundary is migrating further inland," says Dr G Hilmar Gudmundsson from NERC's British Antarctic Survey, a researcher on the project.

The team, which included scientists from the CSC-IT Center for Science in Finland, the Chinese Academy of Sciences and the Universities of Exeter and Bristol, used three computer models as well as field observations to study how the glacier's ice flows and to simulate how this will change over the coming decades.

Not only is more ice flowing from the glacier into the ocean, but it's also flowing faster - Dr Gudmundsson, BAS

All the models agreed that the Pine Island Glacier has become unstable, and will continue to retreat for tens of kilometres.

"The Pine Island Glacier shows the biggest changes in this area at the moment, but if it is unstable it may have implications for the entire West Antarctic Ice Sheet," says Gudmundsson. "Currently we see around two millimetres of sea level rise a year, and the Pine Island Glacier retreat could contribute an additional 3·5 - 5 millimetres in the next twenty years, so it would lead to a considerable increase from this area alone. But the potential is much larger."

Pine Island Glacier currently contributes 25 per cent of the total ice loss from West Antarctica. If the entire West Antarctic Ice Sheet was to retreat, it could cause sea level to rise up to five metres.

"The models show a strong agreement and the result is a striking vision of the near future. All the models suggest that this recession will not stop, cannot be reversed and that more ice will be transferred into the ocean," says Dr Gaël Durand of CNRS, Laboratoire de Glaciologie et de Géophysique de l'Environnement at the University of Grenoble, another researcher on the project.

Gudmundsson doesn't believe that an iceberg the size of Manhattan, which broke off from the Pine Island Glacier last July, will have had any impact on the self-sustained retreat of the grounding line currently seen at the glacier.

"Calving, where an iceberg breaks off from a glacier, does not contribute to sea level rise as the iceberg is already in the ocean so it will have already displaced any water it was going to," Gudmundsson explains.

This work was supported by the ice2sea project, and by NERC grant number NE/H02333X/1.

'Retreat of Pine Island Glacier controlled by marine ice-sheet instability' - L Favier, G Durand, SL Cornford, GH Gudmundsson, O Gagliardini, F Gillet-Chaulet, T Zwinger, AJ Payne and AM Le Brocq (2013), Nature Climate Change, DOI: 10.1038/NCLIMATE2094.