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A new model has been constructed for calculating the level of atmospheric COsub 2 over Phanerozoic time which is much simpler mathematically than the BLAG model, but more complex geologically and biologically. Results suggest that there has been a notable pattern of varying atmospheric COsub 2 level over the past 570 my with high levels during the Mesozoic and early Paleozoic and low levels during the Permo-Carboniferous and late Cenozoic. Sensitivity analysis shows that, within reasonable limits of the principal governing parameters, this qualitative trend of varying COsub 2 is relatively insensitive to the actual values chosen for these parameters. Causes of the COsub 2 variation are multiple, and no single geological or biological process can be called upon to explain all COsub 2 variation for all time. The calculated trend of COsub 2 over time agrees well with independent estimations of paleoclimates. Thus, the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study.
Robert A. Berner (1991) studied this question.