The West Antarctic Ice Sheet: Is It About to Self-Destruct?
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.
In doing so, Naish et al. derived "a marine glacial record from the upper 600 meters of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL program," thereby demonstrating the "well-dated ~40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the earth's axial tilt (obliquity) during the Pliocene."
The 56 researchers report that their data "provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ~3°C warmer than today and atmospheric CO2 concentration was as high as ~400 ppm," the latter of which numbers is only about 12 ppm or 3% greater than what it is today.
An important implication of Naish et al.'s last observation is that the much greater periodic warmth of the early-Pliocene was clearly not the primary result of periodic changes in the air's CO2 concentration; and they tacitly acknowledge that fact by attributing the variable warmth to periodic changes in the planet's axial tilt that produced 40,000-year cycles of insolation. Setting aside that fact, the next most important inquiry into the matter would be how long it took for such warmth to bring about a total collapse of the WAIS, such as Al Gore and James Hansen suggest could occur (geologically speaking, or maybe not!!!) "the day after tomorrow." For the answer to this question, we look to the companion paper of Pollard and DeConto (2009).
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.