The stability of the West Antarctic Ice Sheet is the largest source of uncertainty in estimating future sea level rise. Grounded on rock below sea level, the 3,000-metre-thick ice sheet could disintegrate rapidly if it becomes unstable at its base.
Now a new study by Richard Katz at the University of Oxford and Grae Worster at the University of Cambridge, UK suggests that grounding-line recession — a precursor to ice-sheet loss — may already be underway in Pine Island Glacier (PIG), the largest stream of fast-moving ice on the West Antarctic Ice Sheet.
Writing in Proceedings of the Royal Society A, Katz and Worster use a novel theoretical and mathematical 3D model of the ice sheet to investigate the conditions under which it’s likely to become unstable at its grounding line, where it floats free of its base. They caution that their model is simple, but say that it has an improved physical and mathematical basis compared with previous models, which have been inconclusive on the issue of whether PIG is, in fact, unstable.
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The study shows that PIG has probably passed a critical “tipping point” and is irreversibly on track to lose 50 per cent of its ice in as little as 100 years, significantly raising global sea levels.
The model suggests that within 100 years, PIG’s grounding line could have retreated over 200 kilometres.
The team that carried out the study admits their model can represent only a simplified version of the physics that govern changes in glaciers, but say that if anything, the model is optimistic and PIG will disappear faster than it projects.
Image: Birth of a Large Iceberg in Pine Island Bay, Antarctica in 2001. NASA