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The West Antarctic Ice Sheet: How Fast Could It Collapse?
Reference
Pollard, D. and DeConto, R.M. 2009. Modelling West Antarctic ice sheet growth and collapse through the past five million years. Nature 458: 329-332.

What was done
The authors state that projections of future West Antarctic Ice Sheet (WAIS) behavior "have been hampered by limited understanding of past variations and their underlying mechanisms." With the findings of Naish et al. (2009), however, they gained important new knowledge that helped them frame a greatly-improved "ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years."

What was learned
Pollard and DeConto report that they modeled WAIS variations ranging "from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands." In addition, they say their work suggests that "the WAIS will begin [our italics] to collapse when nearby ocean temperatures warm by roughly 5C." So how long would it take to complete the process?

In a News & Views story on Pollard and DeConto's findings, Huybrechts (2009) states that "the amount of nearby ocean warming required to generate enough sub-ice-shelf melting to initiate a significant retreat of the West Antarctic ice sheet ... may well take several centuries to develop." And once started, he says that the transition time for a total collapse of the West Antarctic ice sheet would range from "one thousand to several thousand years," which time period, in his words, "is nowhere near the century timescales for West Antarctic ice-sheet decay based on simple marine ice-sheet models," such as have been employed in the past.

What it means
Once again, the specter of 21st-century sea level rise being measured in meters -- as hyped by Al Gore and James Hansen -- can be seen to be receding ever further into the distance of unreality.

References
Huybrechts, P. 2009. West-side story of Antarctic ice. Nature 458: 295-296.

Naish, T., Powell, R., Levy, R., Wilson, G., Scherer, R., Talarico, F., Krissek, L., Niessen, F., Pompilio, M., Wilson, T., Carter, L., DeConto, R., Huybers, P., McKay, R., Pollard, D., Ross, J., Winter, D., Barrett, P., Browne, G., Cody, R., Cowan, E., Crampton, J., Dunbar, G., Dunbar, N., Florindo, F., Gebbherdt, C., Graham, I., Hannah, M., Hansaraj, D., Harwood, D., Helling, D., Henrys, S., Hinnov, L., Kuhn, G., Kyle, P., Laufer, A., Maffioli, P., Magens, D., Mandernack, K., McIntosh, W., Millan, C., Morin, R., Ohneiser, C., Paulsen, T., Persico, D., Raine, I., Reed, J., Riesselman, C., Sagnotti, L., Schmitt, D., Sjunneskog, C., Strong, P., Taviani, M., Vogel, S., Wilch, T. and Williams, T. 2009. Obliquity-paced Pliocene West Antarctic ice sheet oscillations. Nature 458: 322-328.

Reviewed 29 April 2009