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Thursday, December 31, 2009

D.O. Breecker et al., PNAS 2009, Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100

Proceedings of the National Academy of Sciences,

Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100

D. O. Breecker**, Z. D. Sharp and L. D. McFadden (MSC03-2040, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, U.S.A.)

Abstract

Quantifying atmospheric CO2 concentrations ([CO2]atm) during Earth’s ancient greenhouse episodes is essential for accurately predicting the response of future climate to elevated CO2 levels. Empirical estimates of [CO2]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 [CO2]atm have been significantly overestimated because previously assumed soil CO2 concentrations during carbonate formation are too high. More accurate [CO2]atm, resulting from better constraints on soil CO2, indicate that large (1,000s of ppmV) fluctuations in [CO2]atm did not characterize ancient climates and that past greenhouse climates were accompanied by concentrations similar to those projected for A.D. 2100.

**Correspondence e-mail: breecker@jsg.utexas.edu.
  • * Graphic, where R equals 13C/12C and the subscripts “sam” and “std” refer to the unknown sample and a standard (Pee Dee Belemnite, PDB), respectively.
  • Soil temperature (needed to calculate Graphic) is typically assumed; Graphic is either held constant (10) or is estimated from the δ13C value of contemporaneous marine carbonates (e.g., 12) or well-preserved organic material (e.g., 8); Graphic is either calculated from Graphic (e.g., 12) or taken to equal the δ13C value of well-preserved organic material (e.g., 8).
Link:  http://www.pnas.org/content/early/2009/12/24/0902323106.abstract

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