Maybe you wish to have a look into one of the Keeling papers?
Have fun, Michael

> Hello All,
> I was told of a journal article discussing the isotope ratio of carbon in
> the atmosphere. Supposedly, the article links the increased atmospheric
> CO2 concentration to anthropogenic sources through this carbon isotope
> ratio.
> Unfortunately, after a couple of weeks of looking for this article, I have
> been unable to find it. Has anyone else come across such an article?
> Either my searching technique is really lacking, or it doesn't exist (the
> article).
> Thanks,
> -Tom Millican
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> University of Arkansas Stable Isotope Laboratory
> http://www.uark.edu/ua/isotope/
>