Two of this sheet's major points, with which we are in total agreement, state that "past natural climate changes offer vital insights into human-induced climate change," and "reconstructions of past climates can be used as a check on climate model projections."
In applying these principles to the temperature and CO2 history of the past 250,000 years, model projections of a future CO2-induced climate change appear to be ill conceived. Take for example the recent findings of Fischer et al. (1999), who examined contemporaneous records of atmospheric CO2 concentration and temperature derived from Antarctic ice cores that extended back in time through the last three glacial-interglacial transitions. They report that in all three of the most recent glacial terminations, the earth warmed well before there was any increase in the air's CO2 content, noting that "the time lag of the rise in CO2 concentrations with respect to temperature change is on the order of 400 to 1000 years." In addition, during the penultimate (next to last) warm period, their study indicates a 15,000-year time interval where distinct cooling does not elicit any change in atmospheric CO2; and when the air's CO2 content gradually drops over the next 20,000 years, air temperatures either rise or remain fairly constant.
The best defined of these relationships between temperature and CO2 appears to suggest just the opposite of what is assumed in all of the climate model studies that warn of dramatic warming in response to the ongoing rise in the air's CO2 content: temperature rises first, and then comes an increase in atmospheric CO2.
So what is one to believe? Theoretical predictions or historical fact? The choice of wisdom would appear to us to be history. It has an uncanny way of repeating itself.
Reference
Fischer, H., Wahlen, M., Smith, J., Mastroianni, D. and Deck B. 1999. Ice core records of atmospheric CO2 around the last three glacial terminations. Science 283: 1712-1714