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The depletion of ¹⁴C due to the emission of radiocarbon-free fossil fuels (¹⁴C Suess effect) might lead to similar values in future and past radiocarbon signatures potentially introducing ambiguity in dating. I here test if a similar impact on the stable carbon isotope via the ¹³C Suess effect might help to distinguish between ancient and future carbon sources. To analyze a wide range of possibilities, I add to future emission scenarios carbon dioxide reduction (CDR) mechanisms, which partly enhance the depletion of atmospheric already caused by the ¹⁴C Suess effect. The ¹³C Suess effect leads to unprecedented depletion in shifting the carbon cycle to a phase space in , in which the system has not been during the last 50 000 years and therefore the similarity in past and future (the ambiguity in ¹⁴C dating) induced by fossil fuels can in most cases be overcome by analyzing ¹³C. Only for slow changing reservoirs (e.g. deep Indo-Pacific Ocean) or when CDR scenarios are dominated by bioenergy with capture and storage the effect of anthropogenic activities on ¹³C does not unequivocally identify between past and future carbon cycle changes.