The West Antarctic Ice Sheet (WAIS) is often described as the world's most unstable large ice sheet. As Hillenbrand et al. (2002) report, "it was speculated, from observed fast grounding-line retreat and thinning of a glacier in Pine Island Bay (Rignot, 1998; Shepherd et al., 2001), from the timing of late Pleistocene-Holocene deglaciation in the Ross Sea (Bindschadler, 1998; Conway et al., 1999), and from predicted activity of ice-stream drainage in response to presumed future global warming (Oppenheimer, 1998), that the WAIS may disappear in the future, causing the sea-level to rise at a rate of 1 to 10 mm/year (Bindschadler, 1998; Oppenheimer, 1998)." Hence, it is important to keep an eye on what is written about the subject in the scientific literature, which is what we do as ever more pertinent papers are published, the findings of a number of which we review in this Summary as they pertain to potential WAIS collapse and disintegration.
Cofaigh et al. (2001) analyzed five sediment cores from the continental rise west of the Antarctic Peninsula and six from the Weddell and Scotia Seas for their ice rafted debris (IRD) content, in an attempt to see if there are Antarctic analogues of the Heinrich layers of the North Atlantic Ocean, which testify of the repeated collapse of the eastern margin of the Laurentide Ice Sheet and the concomitant massive discharge of icebergs. If such IRD layers exist around Antarctica, the researchers reasoned, they would be evidence of "periodic, widespread catastrophic collapse of basins within the Antarctic Ice Sheet," which could obviously occur again. However, after carefully studying their data, they concluded that "the ice sheet over the Antarctic Peninsula did not undergo widespread catastrophic collapse along its western margin during the late Quaternary," and they say this evidence "argues against pervasive, rapid ice-sheet collapse around the Weddell embayment over the last few glacial cycles." And if there was no dramatic break-up of the WAIS over the last few glacial cycles, there's a very good chance there will be none before the current interglacial ends, especially since the data of Petit et al. (1999) indicate that the peak temperatures of each of the previous four intergalcials were warmer than the peak temperature of the current interglacial ... and by an average of more than 2°C.
Hillenbrand et al. (2002) studied the nature and history of glaciomarine deposits contained in sediment cores recovered from the West Antarctic continental margin in the Amundsen Sea to "test hypotheses of past disintegration of the WAIS." In doing so, they found that all proxies regarded as sensitive to a WAIS collapse changed markedly during the global climatic cycles of the past 1.8 million years, but that they "do not confirm a complete disintegration of the WAIS during the Pleistocene" at a place where "dramatic environmental changes linked to such an event should be documented." In fact, they say their results "suggest relative stability rather than instability of the WAIS during the Pleistocene climatic cycles," and they note that this conclusion is "consistent with only a minor reduction of the WAIS during the last interglacial period," citing the work of Huybrechts (1990), Cuffey and Marshall (2000) and Huybrechts (2002).
In another paper we have reviewed that addresses the subject of possible WAIS collapse, O'Neill and Oppenheimer (2002) say the ice sheet "may have disintegrated in the past during periods only modestly warmer (~2°C global mean) than today," and they thus claim that setting "a limit of 2°C above the 1990 global average temperature" -- above which the mean temperature of the globe should not be allowed to rise -- "is justified." If the truth be told, however, a 2°C warming of the globe would likely have little to no impact on the stability of the WAIS.
As we have already noted, for example, the average Antarctic peak temperature of all four of the world's prior interglacials was at least 2°C greater than the Antarctic peak temperature of the current interglacial; yet, in the words of the scientists who developed the pertinent temperature record (Petit et al., 1999), the evidence contained in the core "makes it unlikely that the West Antarctic ice sheet collapsed during the past 420,000 years," which is pretty much the same conclusion that was drawn by Cofaigh et al. In addition, we know from the Vostok ice core record that the peak Antarctic temperature of the most recent prior interglacial was fully 3°C warmer than the peak Antarctic temperature of the interglacial in which we presently live, yet the WAIS still did not disintegrate during that prior time of elevated warmth. Furthermore, we know that throughout the long central portion of the current interglacial (when the most recent peak Antarctic temperature was reached), it was much warmer than it was in 1990 (for references, see our Editorial of 26 June 2002), which is the year from which O'Neill and Oppenheimer's critical 2°C warming increment is measured; and this fact raises the 3°C temperature elevation of the last interglacial relative to the global temperature of 1990 to something on the order of 4 or 5°C, for which, again, there was no evidence of even a partial WAIS disintegration.
Finally, and in spite of the current interglacial's current relative coolness, the Vostok ice core data indicate that the current interglacial has been by far the longest stable warm period of the entire 420,000-year record, which suggests we are probably long overdue for the next ice age to begin, and that we may not have the "5 to 50 centuries" that O'Neill and Oppenheimer suggest could be needed to bring about the WAIS disintegration subsequent to the attainment of whatever temperature in excess of 4 or 5°C above the current global mean would be needed to initiate the process. In conclusion, therefore, it would appear that the climate-alarmist vision of impending WAIS collapse and disintegration is nothing more than an ill-founded hallucination.
References
Bindschadler, R. 1998. Future of the West Antarctic Ice Sheet. Science 282: 428-429.
Cofaigh, C.O., Dowdeswell, J.A. and Pudsey, C.J. 2001. Late Quaternary iceberg rafting along the Antarctic Peninsula continental rise in the Weddell and Scotia Seas. Quaternary Research 56: 308-321.
Conway, H., Hall, B.L., Denton, G.H., Gades, A.M. and Waddington, E.D. 1999. Past and future grounding-line retreat of the West Antarctic Ice Sheet. Science 286: 280-283.
Cuffey, K.M. and Marshall, S.J. 2000. Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet. Nature 404: 591-594.
Hillenbrand, C-D., Futterer, D.K., Grobe, H. and Frederichs, T. 2002. No evidence for a Pleistocene collapse of the West Antarctic Ice Sheet from continental margin sediments recovered in the Amundsen Sea. Geo-Marine Letters 22: 51-59.
Huybrechts, P. 1990. The Antarctic Ice Sheet during the last glacial-interglacial cycle: a three-dimensional experiment. Annals of Glaciology 14: 115-119.
Huybrechts, P. 2002. Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles. Quaternary Science Reviews 21: 203-231.
O'Neill, B.C. and Oppenheimer, M. 2002. Dangerous climate impacts and the Kyoto Protocol. Science 296: 1971-1972.
Oppenheimer, M. 1998. Global warming and the stability of the West Antarctic Ice Sheet. Nature 393: 325-332.
Petit, J.R., Jouzel, J., Raynaud, D., Barkov, N.I., Barnola, J.-M., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., Delmotte, M., Kotlyakov, V.M., Legrand, M., Lipenkov, V.Y., Lorius, C., Pepin, L., Ritz, C., Saltzman, E., and Stievenard, M. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429-436.
Rignot, E.J. 1998. Fast recession of a West Antarctic glacier. Science 281: 549-551.
Shepherd, A., Wingham, D.J., Mansley, J.A.D. and Corr, H.F.J. 2001. Inland thinning of Pine Island Glacier, West Antarctica. Science 291: 862-864.
Last updated 3 September 2008