If the climate change is caused by humans, that is more likely due to deforestation and destruction to nature.
CO2 is used by plants, and plants produce oxygen. If you kill more plants and build concrete cities over where they were...you could get your global warming.
Deforestation and destruction of nature could change CO2 levels, but they don't change the isotope mix of the carbon in atmospheric CO2. We know the increase is mostly coming from something whose carbon has a different isotope mix.
CO2 is used by plants, and plants produce oxygen. If you kill more plants and build concrete cities over where they were...you could get your global warming.