The amount of carbon on the planet is a constant due to the Law of the Conservation of Mass.  Carbon is a RARE life bearing element at only 0.08% mass of the planet, while human life requires 18% by mass carbon!  Oxygen is 49.2%, there is no way that CO2 can become dominant when Oxygen is a dominant molecule.  Humans are 18 to 23% carbon.  All life forms require carbon, our expelled breath CO2 or carbon dioxide plants need to breathe to survive.

TABLE 3.3 Distribution of elements in the Earth’s crust, oceans, and atmosphere