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.
What was done
The authors 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.
What was learned
In all three of the most recent glacial terminations, the earth warmed well before there was any increase in the air's CO2 content. In the words of the authors, "the time lag of the rise in CO2 concentrations with respect to temperature change is on the order of 400 to 1000 years during all three glacial-interglacial transitions." During the penultimate (next to last) warm period, there is also 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.
What it means
One of the reasons for conducting studies of this type is to see what can be learned about the ability of increases in atmospheric CO2 to enhance earth's natural greenhouse effect and induce global warming. As is readily evident from the work described here, however, the relationship between temperature and CO2 appears to be just the reverse 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. Or, CO2 remains essentially unchanged while temperatures drop. Or, CO2 drops while air temperature remains unchanged or actually rises. Nothing even comes close to resembling what we are continually being warned about by state-of-the-art global climate models.
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.
Reviewed 15 April 1999