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From: rparson@spot.Colorado.EDU (Robert Parson)
Newsgroups: sci.chem
Subject: Re: Global Warming Higher Than Expected
Date: 16 Jul 1999 16:57:49 GMT

In article <7mdmqv$odk$>,
Superdave the Wonderchemist <> wrote:
>Interesting...  So what is the 14-C dilution factor?  Fossil fuels contain
>almost no 14-C (since they've been underground for too many millions of
>years).  Therefore, C-14 dilution should be a wonderful way to determine
>anthropomorphicly induced atmospheric CO2 increases.

 Indeed it is - it even has a name, the "Suess Effect", after the
 geochemist who first detected it in the 1950's. The original reference
 is H. Suess, _Science_ _122_, 415 (1955); a more recent one is
 M. Stuiver and P. D. Quay, "Atmospheric C-14 changes resulting from
 fossil fuel CO2 release and cosmic ray flux variability", _Earth and
 Planetary Science Letters_, _53_, 349, 1981. Figure 2 of this paper has
 exactly what you're looking for, tree-ring derived atmospheric C-14
 from 1820 to 1954. There is a clear secular decline in Delta-C-14
 of about 25 per mil betweenm 1900 and 1950.

 As others have remarked, the nuclear tests of the 1950's, which doubled
 atmospheric C-14 over a period of a decade, throw a monkey wrench into
 this analysis. Since the cessation of the tests in ~1963 atmospheric
 C-14 has been rapidly declining, with Delta-C-14 dropping from nearly
 twice the pre-bomb level in 1965 to about 20 percent above the pre-
 bomb level in 1990. (R. Nydal and J. S. Gislefoss, _Radiocarbon_ _38_,
 389, 1996). This decline is due primarily to atmosphere-ocean exchange
 the effect of fossil-fuel dilution is in the noise by comparison. (In
 fact, the atmospheric C-14 decline is one of the primary methods for
 measuring the rate of carbon exchange between air and seawater, a very
 complicated problem involving nasty multiple ionic equilibria plus
 the effects of wind speed and ocean temperature. If you want somebody
 who _really_ understands ionic equilibria in aqueous solution, look for
 a chemical oceanographer.)

 See also _Tracers in the Sea_, by Broecker and Peng, and _Numerical
 Adventures in Geochemical Cycles_, by James Walker (Oxford 1991). The
 latter book teaches you how to calculate these things for yourself,
 and uses the Suess Effect as an example.


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