Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100.
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
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DO
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA.
Sharp
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ZD
McFadden
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LD
D002119:Calcium Carbonate / Q000032:analysis; D002245:Carbon Dioxide / Q000032:analysis*; D003889:Desert Climate; D005544:Forecasting; D005580:Fossils; D017752:Greenhouse Effect; D009516:New Mexico; D010163:Paleontology; D006109:Poaceae; D012621:Seasons; D012987:Soil / Q000032:analysis; D013781:Texas
D012987:Soil; D002245:Carbon Dioxide; D002119:Calcium Carbonate