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) Sioux Center, IA 51250
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