West Antarctica's Future Melting was Revealed in High-Resolution Projections

New research has revealed a more-comprehensive projection of West Antarctica's future, using a high-resolution, large-scale computer model. The amount of ice that the continent could lose over the next few centuries could drastically affect sea-level rise.

The West Antarctica Ice Sheet (WAIS) is one of the fastest warming regions on Earth and has recently experienced dramatic thinning due to an imbalance of melting and renewing snowfall, according to a study recently published in The Cryosphere, an open access journal of the European Geosciences Union. As a result, the ice that does melt, drains through several ice streams and greatly contributes to current sea-level rise. The rate of WAIS ice melting is only expected to increase in the future.

"The IPCC's [Intergovernmental Panel on Climate Change] 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 that models were unable to satisfactorily quantify that response," Stephen Cornford, a research assistant at the University of Bristol, U.K. and lead-author of the study, said in a statement.

Cornford, along with Dan Martin, co-author from the Lawrence Berkeley National Laboratory in California, U.S.; and a team of researchers from around the world, have now estimated just how much the WAIS could contribute to future global sea-level rise, in a more accurate way than previous models allowed.

"The novel aspect of our work is the use of a high-resolution ice-sheet model over a larger area and longer time-scale than previously attempted. Much like a higher-resolution digital camera transforms a blur into a flock of birds, higher resolution in a computer model often helps to capture details of the physics involved which may be crucial to the broad picture," explained Martin.

Their high-resolution, computationally demanding simulations allowed the researchers to take into consideration the uncertainty of future greenhouse gas emissions and snowfall and ocean circulation, in order to reduce the numerical error that is often present using ice-flow models.

"We expect future change in the West Antarctic Ice Sheet to 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," explained Cornford in the release.

According to their study, in the most extreme simulation, ice shelves progressively disintegrate over the next century, while the major ice streams retreat by hundreds of kilometers. In this situation, the WAIS as a whole would contribute some 80,000 cubic kilometers of lost ice to sea-level rise by 2100 and 200,000 cubic kilometers by 2200. This quantity of melting corresponds to a 20 cm global sea level rise by the end of this century, and close to a 50 cm increase by 2200. While this simulation is an extreme circumstance, these amounts would fill the Caspian Sea and be enough to threaten low-lying cities and countries.

"There are many climate processes lying between the direct consequences of greenhouse-gas emissions and the regional ocean warming used as forcing in the modeling reported in The Cryosphere, many of which are poorly understood," explains co-author Tony Payne, a professor at the University of Bristol, in the release. "It would therefore be premature to attach a likelihood to any particular retreat scenario; however, it is useful to quantify the magnitude of sea-level rise in some of these more extreme cases."

While conducting this study, researchers wanted to predict how the WAIS would respond to both modest and extreme future warming. "We subjected an ice dynamics model to a range of ocean and atmospheric changes, ranging from no change at all, through the future changes projected by state-of-the-art ocean and atmosphere models, to extreme changes intended to study the upper reaches of future sea-level rise," explained Cranford in the release.

Payne added that, "The research involved many different steps as the results of global climate models were fed into regional models of the Antarctic atmosphere and ocean, whose results were in turn used to force the ice-sheet model in this study."

Compared to previous calculations using a lower resolution or scale, the predictions of this study are a significant improvement. This allows researchers to make more accurate future predictions of the West Antarctic Ice Sheet's fate and how its unbalanced melting will ultimately affect global sea-level rise.

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