Key points are not available for this paper at this time.
Quantifying atmospheric CO(2) concentrations (CO(2)(atm)) during Earth's ancient greenhouse episodes is essential for accurately predicting the response of future climate to elevated CO(2) levels. Empirical estimates of CO(2)(atm) during Paleozoic and Mesozoic greenhouse climates are based primarily on the carbon isotope composition of calcium carbonate in fossil soils. We report that greenhouse CO(2)(atm) have been significantly overestimated because previously assumed soil CO(2) concentrations during carbonate formation are too high. More accurate CO(2)(atm), resulting from better constraints on soil CO(2), indicate that large (1,000s of ppmV) fluctuations in CO(2)(atm) did not characterize ancient climates and that past greenhouse climates were accompanied by concentrations similar to those projected for A.D. 2100.
Breecker et al. (Mon,) studied this question.