Concentrações de CO2 atmosférico durante os climas tipo efeito estufa antigos foram semelhantes aos preditos para o ano 2100

terça-feira, dezembro 29, 2009

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

D. O. Breecker1,2, Z. D. Sharp and L. D. McFadden
- Author Affiliations

MSC03-2040, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131

↵1 Present address: Department of Geological Sciences, University of Texas, Austin, TX 78712

Edited by Thure E. Cerling, University of Utah, Salt Lake City, UT, and approved October 22, 2009 (received for review March 5, 2009)


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.

paleosol barometer carbon isotopes pedogenic carbonate Phanerozoic climate sensitivity


2To whom correspondence should be addressed. E-mail:

Author contributions: D.O.B., Z.D.S., and L.D.M. designed research; D.O.B. performed research; D.O.B. and Z.D.S. analyzed data; and D.O.B. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

* , 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 ) is typically assumed; 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); is either calculated from (e.g. 12) or taken to equal the δ13C value of well-preserved organic material (e.g. 8).


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