Re: Another apologetical mess up--CO2 in atmosphere

From: James Mahaffy (mahaffy@mtcnet.net)
Date: Tue Mar 28 2000 - 07:29:40 EST

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    Folks,

    Just a few things on Glenn's post on CO2. Glenn's posting the data on
    carbon dioxide in the atmosphere could give the impression to the reader
    that we can directly measure the amount of carbon dioxide that was
    present at various times. Glenn did not imply we could, but citing the
    figures without indicating the method used to come up with them may give
    the reader the wrong impression. I have not read the article but am
    assuming it is the ratio of some isotopes (perhaps C) in rocks
    (?limestones). The indirect method may be a valid way of approximating
    Carbon dioxide [and it may be the only way we can do it] but I would
    like to know how it was calculated and what assumptions were made to
    come up with the calculation. Even the amount of error that results in
    direct measurements should be standard in citing data and I assume the
    error is potentially larger in indirect measurements like these. I know
    in the past assumptions about early atmosphere have changed quite a bit.
    That is not to say these figures may not be right but just to cite them
    gives them more strength than I would feel confident without
    understanding what they are based on.

    I would also caution that climatic modeling applied to the past should
    be taken with a lot of tentativeness. It is still interesting and may be
    right. I for instance was fascinated by modeling Crawley has done
    suggesting that coal formation occurred in a temperate everwet and not
    tropical environment. On the other hand my advisor (who is one of the
    leading paleobotanist studying Carboniferous coal - does not believe it
    - the modeling goes against the traditional assumption of tropical
    nature of those swamps) The reference is - Crowley, T.J., 1994 Pangean
    climates. In: Klein, G. D., (Editor), Pangea: Paleoclimate, Tectonics,
    and Sedimentation During Accretion, Zenith, and Breakup of a
    Supercontinent. Geol. Soc. Amer. Spec. Pap., 288:57-73. I have no idea
    if Crowley's modeling really fits with Raymo [since I have not read
    Raymo] who Glenn cites, but my initial feeling is it sounds different
    from Crowley who I do know, so the reader should be aware that some of
    the explanations are more tentative.

    All this is not to say that Glenn's criticism of Ross may not be
    correct, I am only concerned with not giving the wrong impression to the
    reader in what is know for sure about fossil carbon dioxide and
    paleozoic or earlier climates and what caused those changes. Sometimes
    we are more at the level of guesses than certainty.

    -- 
    James and Florence Mahaffy    712 722-0381 (Home)
    227 S. Main St.              712 722-6279 (Office)
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