> But there have been way higher atmospheric carbon dioxide levels historically

Historically? In written human history?

If we're talking the state of the planet throughout the past 4 billion odd years of existence, it once had no breathable atmosphere and had a stretch with a largely molten surface, and got smacked up hard when the moon was spun off.

None of these things are relevant to the planets near future as a direct result of human induced changes of the past century and a half.