Most Comprehensive Projections for West Antarctica’s Future Revealed
A new international study, with important contributions by researchers from Lawrence Berkeley National Laboratory supported by the Department of Energy’s Scientific Discovery through Advanced Computing (SciDAC) program, is the first to use a high-resolution, large-scale computer model to estimate how much ice the West Antarctic Ice Sheet (WAIS) could lose over the next couple centuries, and how much that ice loss could add to sea-level rise. The results provide a more precise estimate of West Antarctica’s future than was previously possible. The Intergovernmental Panel on Climate Change’s 4th and 5th Assessment Reports both note that the acceleration of West Antarctic ice streams in response to ocean warming could result in a major contribution to sea-level rise, but the models were unable to satisfactorily quantify that response. The novel aspect of this study is the use of a high-resolution ice-sheet model over a larger area and longer time scale than previously attempted, which helps to capture details of the physics involved that may be crucial to the broad picture. West Antarctica is one of the fastest warming regions on Earth, and its ice sheet has dramatically thinned in recent years. The WAIS is out of balance because it is losing significant amounts of ice to the ocean, and these losses are not being offset by snowfall. The lost ice, drained by the ice sheet’s several ice streams, amounts to a significant contribution to sea-level rise, which is expected to increase in the future. The research results reflect uncertainty in future greenhouse gas emissions, snowfall, and ocean circulation, but the choice of a high-resolution model enabled the researchers to reduce the numerical error that often plagues ice-flow models. The simulations indicate that future WAIS change would be dominated by thinning in the Amundsen Sea Embayment, just as it is today, until at least the 22nd century. But other regions of West Antarctica could thin to a similar extent if the ocean warms sufficiently. In their most extreme simulation, where the ice shelves progressively disintegrate over the next century, most of the major ice streams retreat by hundreds of kilometers. The WAIS as a whole would contribute some 80,000 km3 of lost ice to sea-level rise by 2100 and 200,000 km3 by 2200. This ice loss corresponds to a 20-cm increase in global sea level by the end of this century—enough to fill the Caspian Sea—and close to 50 cm by 2200. While these amounts would be enough to threaten low-lying cities and countries, the researchers point out this is an extreme scenario. This comprehensive high-resolution study is a significant improvement from previous calculations, which were lower in resolution or scale, enabling researchers to make more accurate predictions about West Antarctica’s future.
Cornford, S. L., D. F. Martin, A. J. Payne, E. G. Ng, A. M. Le Brocq, R. M. Gladstone, T. L. Edwards, S. R. Shannon, C. Agosta, M. R. van den Broeke, H. H. Hellmer, G. Krinner, S. R. M. Ligtenberg, R. Timmermann, and D. G. Vaughan. “Century-Scale Simulations of the Response of the West Antarctic Ice Sheet to a Warming Climate,” The Cryosphere 9, 1579-1600. DOI: 10.5194/tc-9-1579-2015, 2015.