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|Evidence found of positive feedbacks
by Gerhard Krinner
Pine Island Glacier is the Antarctic glacier which contributes most to the rise in sea level. An international team of researchers led by the Laboratoire de Glaciologie et Géophysique de l’Environnement (Laboratory of Glaciology and Environmental Geophysics LGGE) in France has shown that this contribution could grow by between three and five times in the next twenty years increasing sea levels by up to 10mm. Scientists have also shown that the glacier is receding irreversibly and that it would, in all likelihood, not return to its initial state. Their work was published on 12 January 2014 on the website of the journal Nature Climate Change.
For twenty years now, the West Antarctic has contributed significantly to the rise in sea level. Pine Island Glacier, located in the western part of Antarctica is the largest contributor to this increase: it alone represents nearly 25% of the contribution of West Antarctic melt water. The edge receded ten kilometers from the 2000s and the glacier is tending to thin more. The eastern part of Antarctica remains in equilibrium for now (that is, the amount of ice that accumulates is equal to that lost snow glaciers feeding).
The coastal Pine Island Glacier is therefore the subject of special attention. The international team supported by LGGE (CNRS / UJF) has carefully studied the glacier to better understand its future.
Scientists have relied on threeof the latest generation of computer models of flow of the ice in the polar caps. All three models shows that the glacier is likely ito be unstable and will continue to reced for at least forty kilometers over the next fifty years. The mass loss associated with this irreversible decline is expected to increase significantly from the average value of 20 gigatonnes per year observed during the period 1992 to 2011, up to 120 gigatonnes per year over fifty years modeled. Thus, its annual contribution to rising sea levels could rise by three to five times.This loss would result in an increase in sea level ranging between 3.5 and 10 mm in the next twenty years.
Over the past 40 years Pine Island Glacier in West Antarctica has thinned at an accelerating rate, so that at present it is the largest single contributor to sea-level rise in Antarctic. In recent years, the grounding line, which separates the grounded ice sheet from the floating ice shelf, has retreated by tens of kilometres. At present, the grounding line is crossing a retrograde bedrock slope that lies well below sea level, raising the possibility that the glacier is susceptible to the marine ice-sheet instability mechanism. Here, using three state-of-the-art ice-flow models, we show that Pine Island Glacier’s grounding line is probably engaged in an unstable 40 km retreat. The associated mass loss increases substantially over the course of our simulations from the average value of 20 Gt yr−1 observed for the 1992–2011 period, up to and above 100 Gt yr−1, equivalent to 3.5–10 mm eustatic sea-level rise over the following 20 years. Mass loss remains elevated from then on, ranging from 60 to 120 Gt yr−1.
Retreat of Pine Island Glacier controlled by marine ice-sheet instability by L. Favier, G. Durand, S. L. Cornford, G. H. Gudmundsson, O. Gagliardini, F. Gillet-Chaulet, T. Zwinger, A. J. Payne & A. M. Le Brocq published in Nature Climate Change (2014) doi:10.1038/nclimate2094
Read the abstract and get the paper here.
This report courtesy Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE) here.
Our report "Pine Island Glacier Melt Slowed By La Nina" here.
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