The AD time series of DELTAcarbon-14, deltacarbon-13, and cosmic ray fluxes, Q, were analyzed for similarities. Two cases of significant correlation between Q and tree-ring deltacarbon-13 were encountered, for which up to 25 percent of the variance can be attributed to changes in the tree's isotope fractionation that related to solar induced climatic changes. It is possible that the demonstrated correlation is fortuitous because actual climate proxy records generally do not correlate significantly with the Q record. The history of carbon-13/carbon-12 and carbon-14/carbon-12 ratios in atmospheric carbon dioxide can be obtained from tree-ring cellulose because the carbon of the ring's cell walls is derived from the atmospheric carbon dioxide source. Isotope fractionation in the photosynthetic process adds another signal, and the measured carbon isotopic record in tree rings gives the sum-total of the isotope variation in atmospheric carbon dioxide (which can be of global and local origin), and the variability in isotope fractionation of the plant. By normalizing on a constant carbon-13/carbon-12 ratio, a carbon-14/carbon-12 record can be derived independently of the tree's variability in isotope fractionation. The derivation of a carbon-13/carbon-12 record solely reflecting atmospheric change is more difficult because here the factors influencing the plant's isotope fractionation have to be known in detail. -- AATA