Twice the co2 and life was abundant. No problems at all.
.
No twice the oxygen levels,if I would have meant Co2 I would have written it.
As for life being abundant,well yes but there were very few mammals,mostly Dino’s and insects on land with plenty of fish in the sea….
Personally I doubt it,meaning climate change/weather will have any effect on me but that doesn’t stop me from worrying about the world we’ll leave behind for my grandson and his children.