Climate alarmists such as O'Neill and Oppenheimer (2002) regularly invoke the mere possibility of an abrupt-and-rapid warming resulting from the ongoing rise in the air's CO2 concentration as sufficient reason to implement the Kyoto Protocol [see our Editorial of 10 July 2002]. Since almost anything is possible, however, it makes much more sense to consider an event's likelihood when trying to decide what to do about it. One good way of doing this within the context of potential global warming is to see how often rapid climatic changes have occurred in the past and under what circumstances they occurred, especially with respect to the air's CO2 content. Hence, we take this tack in the following paragraphs.
Staufer et al. (1998) derived a common timescale for earth's last glacial period based on records of atmospheric methane concentrations obtained from Greenland and Antarctica, which they then used to compare climatic oscillations inferred from Greenland ice cores with variations in atmospheric CO2 concentration inferred from Antarctic ice cores. Doing so, they documented a number of rapid warmings of several degrees Centigrade that were followed by slower coolings that returned the climate to full glacial conditions, over which entire cycle the air's CO2 concentration typically varied by less than 10 ppm. Furthermore, the weak correspondence between the two parameters was considered to have been caused by the change in climate, rather than by the change in CO2, suggesting that variations in atmospheric CO2 concentration had absolutely nothing to do with the large and abrupt warming events.
Rahmstorf (2003) analyzed the GISP2 ice core record from Greenland with respect to the timing of Dansgaard-Oeschger (DO) warm events, finding these abrupt climate changes "appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent." With 95% confidence, for example, the period is maintained to better than 12% over at least 23 cycles during the time interval of 51 to 10 thousand years before present. In fact, Rahmstorf reports that "the five most recent events, arguably the best-dated ones, have a standard deviation of only 32 years (2%)." This finding, in his words, "strongly supports the idea that the events are paced by a regular 1,470 year cycle," and he says that "the highly precise clock points to an origin outside the Earth system," which once again lets CO2 off the hook as being the cause of the warmings.
On a much finer timescale, Overpeck and Webb (2000) discuss what we know about the abrupt-and-rapid climatic variability associated with the ENSO phenomenon during the current interglacial or Holocene. They note that shifts in ENSO frequency during this period occurred at both interannual and multidecadal intervals, providing evidence that "ENSO may change in ways that we do not yet understand," but which are clearly not related to atmospheric CO2 concentration. In fact, they say data from corals suggest that "interannual ENSO variability, as we now know it, was substantially reduced, or perhaps even absent," during the middle of the Holocene, when atmospheric CO2 concentrations were not much different from what they were immediately before or after that period.
Moving slightly closer to the present, Rietti-Shati et al. (1998) derived a 3,000-year climatic history for a high-altitude region on Mount Kenya in East Africa for the period 4200-1200 years before present via oxygen isotope analysis of biogenic opal extracted from a sediment core retrieved from a shallow lake. Among numerous small temperature fluctuations, they detected a significant warming that occurred between 2,300 and 2,000 years ago, when temperatures rose approximately 4°C in just three centuries, consistent with other proxy temperature records of Mount Kenya's surroundings. Again, however, there were no dramatic fluctuations of atmospheric CO2 concentration associated with this event.
In China, Yafeng et al. (1999) analyzed high-resolution records of ð18O obtained from the Guliya ice cap of the Qinghai-Tibet Plateau to derive a 2000-year temperature history of that part of the world. Perhaps their most striking discovery was the identification of 33 abrupt climatic shifts on the order of 3°C that took place over the course of two or three decades, among which were "several large ones," including a 7°C decrease between 250 and 280 AD and a 7°C increase between 550 and 580 AD, when, of course, the air's CO2 concentration was low and unchanging.
Schuster et al. (2000) employed electrical conductivity measurements, scanning electron microscopy, energy dispersive analysis, and isotopic and chemical analyses to study a 160-meter ice core removed from Wyoming's Upper Fremont Glacier, finding, in their words, that "the termination of the Little Ice Age was abrupt with a major climatic shift to warmer temperatures around 1845 A.D." They also note that "a conservative estimate for the time taken to complete the Little Ice Age climatic shift to present-day climate is about 10 years," over which period the atmosphere's CO2 concentration rose by about 1 ppm.
Last of all, we note the study of Cronin et al. (2000), who studied the salinity gradient across sediment cores from Chesapeake Bay, which is the largest estuary in the United Sates, in an effort to examine, not temperature, but precipitation variability over the past thousand years. A high degree of decadal and multidecadal variability between wet and dry conditions was noted throughout the record, where regional precipitation totals fluctuated by 25 to 30%, often in extremely rapid shifts occurring over about a decade.
These several observations demonstrate that abrupt-and-rapid climate changes have occurred numerous times in the past, all without any help from changes in the air's CO2 content. In fact, there is no conclusive evidence that any such climate changes have ever been produced by either increases or decreases in atmospheric CO2 concentration such as are capable of being produced by the actions of man. Hence, to suggest we must ratify the Kyoto Protocol to protect the planet from another such abrupt-and-rapid climate change seems highly irrational.
References
Cronin, T., Willard, D., Karlsen, A., Ishman, S., Verardo, S., McGeehin, J., Kerhin, R., Holmes, C., Colman, S. and Zimmerman, A. 2000. Climatic variability in the eastern United States over the past millennium from Chesapeake Bay sediments. Geology 28: 3-6.
O'Neill, B.C. and Oppenheimer, M. 2002. Dangerous climate impacts and the Kyoto Protocol. Science 296: 1971-1972.
Overpeck, J. and Webb, R. 2000. Nonglacial rapid climate events: Past and future. Proceedings of the National Academy of Sciences USA 97: 1335-1338.
Rahmstorf, S. 2003. Timing of abrupt climate change: A precise clock. Geophysical Research Letters 30: 10.1029/2003GL017115.
Rietti-Shati, M., Shemesh, A. and Karlen, W. 1998. A 3000-year climatic record from biogenic silica oxygen isotopes in an equatorial high-altitude lake. Science 281: 980-982.
Schuster, P.F., White, D.E., Naftz, D.L. and Cecil, L.D. 2000. Chronological refinement of an ice core record at Upper Fremont Glacier in south central North America. Journal of Geophysical Research 105: 4657-4666.
Staufer, B., Blunier, T., Dallenbach, A., Indermuhle, A., Schwander, J., Stocker, T.F., Tschumi, J., Chappellaz, J., Raynaud, D., Hammer, C.U. and Clausen, H.B. 1998. Atmospheric CO2 concentration and millennial-scale climate change during the last glacial period. Nature 392: 59-62.
Yafeng, S., Tandong, Y. and Bao, Y. 1999. Decadal climatic variations recorded in Guliya ice core and comparison with the historical documentary data from East China during the last 2000 years. Science in China Series D-Earth Sciences 42 Supp.: 91-100.