Graph showing CO2 level parking at 1600 ppm 51 million years ago and gradually decreasing, with a bump of 480 ppm 16 million years ago, to around 270 ppm for the last 2 million years or so.
https://sfo3.digitaloceanspaces.com/cdn.mastodon.energy/media_attachments/files/111/543/386/748/307/298/original/1a30612603dbd7f3.jpg