The climate of the Earth, including the CO2 concentration of the atmosphere, has undergone a large variety of changes of great magnitudes due to differing natural causes over different time scales in its very long past.
However, human existence let alone thriving in humanity's current numbers is predicated on a pretty narrow set of conditions. It is not the Earth and life on it themselves we should be worrying about particularly over geological timescales. It is the rapidity of change brought about by the impact of our civilization - on ourselves - that should concern us.