Basically, when you look at different types of cells, such as fibroblasts, which form connective tissue, or epithelial cells, from saliva,
you see general correlations within a person.
I will try to get some more specific answers for you and either correct or fill out this article, but I think the main gist of the argument is that there are other factors at play and the simple lack of a perfect
correlation does not mean that CO2 is not the primary driver of the
general warming
seen since 1900.