Rothman, D.H. 2002. Atmospheric carbon dioxide levels for the last 500 million years. Proceedings of the National Academy of Sciences USA 99: 4167-4171.
What was done
Based on considerations related to the chemical weathering of rocks, volcanic and metamorphic degassing, and the burial of organic carbon, along with considerations related to the isotopic content of organic carbon and strontium in marine sedimentary rocks, the author derived a 500-million-year history of the air's CO2 content.
What was learned
Over the bulk of the record, earth's atmospheric CO2 concentration fluctuates between values that are two to four times greater than that of today at a dominant period on the order of 100 million years. For the last 175 million years, however, there has been a rather steady long-term decline in the air's CO2 content.
What it means
The author states that it is "interesting to ask what, if any, correspondence exists between ancient climate and the [newly derived CO2] estimate." Indeed, it is very interesting to ask that question; for the political future of the entire world rests on the validity or invalidity of the climate-alarmist supposition that changes in the air's CO2 content are major determinants of changes in climate. So what do the new results show?
Rothman reports that the CO2 history he derived "exhibits no systematic correspondence with the geologic record of climatic variations at tectonic time scales." In another place he writes that "comparison with the geologic record of climatic variations reveals no obvious correspondence." And in yet another place he says that although the most recent cool period corresponds to the relatively low CO2 levels of the present, "no correspondence between atmospheric CO2 concentration and climate is evident in the remainder of the record."
If the truth be told, however, a simple visual examination of the author's plot of CO2 and climate vs. time clearly indicates that the three most striking peaks in the atmospheric CO2 record occur either totally or partially within periods of time when earth's climate was relatively cool. Hence, not only is there no proof for the climate-alarmist contention that higher CO2 concentrations tend to warm the planet, there is evidence in this study to suggest that just the opposite may be true.
Reviewed 8 May 2002