[throwaway15908]

>Why are 200ppm sustainable?

The higher CO2 levels of long gone times where probably not even remotely a problem for those critters around, because evolution had plenty of time to do its thing. Your whole point of "but what about back then" is comparing apples with oranges.

Looking at the steep graph today, the increasing weather extremes and how brittle our supply chains are, i think its very appropriate to call it a climate catastrophe, we are heading for.

Btw. I was using the ideal of perfect recycling and applied it to CO2, no absolute or relative ppm value is relevant for this.