Carbon dioxide in our atmosphere may soar to levels not seen in 56 million years
...That era, known by scientists as the Paleocene-Eocene Thermal Maximum (PETM), was Earth's warmest period since the extinction of the dinosaurs 66 million years ago. According to the study, during that period, the poles were ice-free, and the Arctic was home to palm trees and crocodiles.
That warmth caused a major extinction of organisms in the deep ocean that are a key link in the marine food web...
https://www.yahoo.com/news/carbon-dioxide-atmosphere-may-soar-130003384.html