Within this context, it is important to know what the proponents of the Protocol consider a dangerous climate impact worthy of immediate action.  Taking the Intergovernmental Panel on Climate Change as their guide, O'Neill and Oppenheimer (2002) say it is an impact that either imposes a risk upon unique and threatened ecosystems or engenders a risk of some large-scale discontinuity in earth's climate system.  On this basis, they claim there are three warming-related risks that are serious enough to implement the Kyoto Protocol with all due haste.  These risks are the potentials for (1) the infliction of extreme damage to earth's coral reefs, (2) the disintegration of the West Antarctic Ice Sheet, and (3) the virtual shutdown of the marine thermohaline circulation.

With respect to the second of these risks - we dealt with the first one in our Editorial of 26 June 2002 - O'Neill and Oppenheimer (hereafter, O & O) claim that limited evidence from proxy data suggests the West Antarctic Ice Sheet (WAIS) "may have disintegrated in the past during periods only modestly warmer (~2°C global mean) than today."  Thus, they say 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 to protect [the] WAIS."

If the truth be told, however, a 2°C warming of the globe would likely have little impact on the stability of the WAIS.  How do we know?  By the icy beast's past performance.

Based on a 420,000-year temperature record derived from the Vostok ice core, we know, first of all, that the mean temperature of all four of the prior interglacials was at least 2°C greater than the mean temperature of the current interglacial; yet, in the words of the scientists who developed the 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."  This is pretty much the same conclusion that was subsequently drawn by Cofaigh et al. (2001), who on the basis of analyses of sediment cores taken from the continental rise west of the Antarctic Peninsula and the Weddell and Scotia Seas concluded that "the ice sheet over the Antarctic Peninsula did not undergo widespread catastrophic collapse along its western margin during the late Quaternary," and who say that their evidence "argues against pervasive, rapid ice-sheet collapse around the Weddell embayment over the last few glacial cycles."

Second, we know from the Vostok temperature record that the most recent interglacial was fully 3°C warmer than the interglacial in which we presently live, but that the WAIS still did not disintegrate.  Third, we know that throughout the long central portion of the current interglacial it was also much warmer than it was in 1990 [see our Editorial of 26 June 2002 for references], which is the year from which O & O's 2°C critical 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 still no WAIS disintegration.

Fourth, and in spite of the current interglacial's relative coolness, the Vostok ice core data indicate that it 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, and that we may not have the "5 to 50 centuries" that O & O say could be required to bring about the WAIS disintegration subsequent to the attainment of whatever temperature in excess of 4 or 5°C would be needed to initiate the process.

Other evidence of the inability of the significant warmth of the last interglacial to trigger the disintegration of the WAIS was provided in a roundabout way by the study of Cuffey and Marshall (2000), whose reevaluation of the Greenland ice sheet's contribution to the sea level rise of that period suggests that the Greenland ice sheet was much smaller at that time than had previously been thought.  In light of this finding, Hvidberg (2000) was prompted to conclude that the "high sea levels during the last interglacial should not be interpreted as evidence for extensive melting of the West Antarctic Ice Sheet, and so challenges the hypothesis that the West Antarctic is particularly sensitive to climate change."

Additional evidence that the climatic behavior of Antarctica is not particularly sensitive to what is happening in the rest of the world is provided by the study of Comiso (2000), who assembled and analyzed Antarctic temperature data from 21 surface stations and infrared satellites that operated from 1979 to 1998.  In spite of the fact that much of the rest of the world may have warmed somewhat over this period, Comiso found that both Antarctic data sets depicted a slight cooling over the last 20 years.  This was also the conclusion of the more recent study of Doran et al. (2002), whose spatial analysis of Antarctic meteorological data demonstrated a net cooling between 1966 and 2000, which for the McMurdo Dry Valleys between 1986 and 2000 averaged 0.7°C per decade.

Still more support for this intriguing disconnect was provided by Watkins and Simmonds (2000).  Analyzing satellite data obtained from December 1987 through December 1996, they observed statistically significant increases in both sea ice area and extent; and combining their results with earlier results for the period 1978-1987, both parameters showed increases over the entire 1978-1996 period.  They also found that the 1990s exhibited increases in the length of the sea ice season.  Thus, it is not surprising that in another satellite study of Antarctic sea ice extent, Yuan and Martinson (2000) determined that the net trend in the mean Antarctic sea ice edge over the prior 18 years was an equatorward expansion of 0.011 degree of latitude per year.

In view of these several real-world observations, we feel there is no justification for O & O's claim that "a limit of 2°C above [the] 1990 global average temperature is justified to protect [the] WAIS."  There is no convincing evidence that within the past half-million years of periodically much higher temperatures it has ever disintegrated or even come close to doing so, or that within the past quarter-century of supposedly "unprecedented" global warming it has even gotten any warmer.  In fact, the ice-covered continent has done just the opposite; it has cooled.  Therefore, to claim that the highly improbable collapse of the WAIS is one of the three most compelling reasons to implement the Kyoto Protocol is, well, music to our ears, as it shows just how desperate the folks in favor of CO2 emissions regulation have become.

Reference
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.

Comiso, J.C.  2000.  Variability and trends in Antarctic surface temperatures from in situ and satellite infrared measurements.  Journal of Climate 13: 1674-1696.

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.

Doran, P.T., Priscu, J.C., Lyons, W.B., Walsh, J.E., Fountain, A.G., McKnight, D.M., Moorhead, D.L., Virginia, R.A., Wall, D.H., Clow, G.D., Fritsen, C.H., McKay, C.P. and Parsons, A.N.  2002.  Antarctic climate cooling and terrestrial ecosystem response.  Nature 415: 517-520.

Hvidberg, C.S.  2000.  When Greenland ice melts.  Nature 404: 551-552.

O'Neill, B.C. and Oppenheimer, M.  2002.  Dangerous climate impacts and the Kyoto Protocol.  Science 296: 1971-1972.

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.

Watkins, A.B. and Simmonds, I.  2000.  Current trends in Antarctic sea ice: The 1990s impact on a short climatology.  Journal of Climate 13: 4441-4451.

Yuan, X. and Martinson, D.G.  2000.  Antarctic sea ice extent variability and its global connectivity.  Journal of Climate 13: 1697-1717.