https://phys.org/news/2018-07-ever-increasing-co2-tropical-climate-paleogene.html

The early Paleogene is a period of great interest to climate change scientists as carbon dioxide levels (around 1,000 ppmv) are similar to those predicted for the end of this century.

Dr. David Naafs from the University of Bristol's School of Earth Sciences, led the research published today in the journal, Nature Geoscience. He said: "We know that the early Paleogene was characterised by a greenhouse climate with elevated carbon dioxide levels.