How atmospheric CO₂ has changed over 60 million years

Pre-industrial global CO2 concentration from proxies in marine and terrestrial records

Earth's atmospheric CO₂ levels have risen and fallen naturally over millions of years. This chart reconstructs that history — from 60 million years ago to pre-industrial times — using chemical signals preserved in marine sediments and ancient plant material. Concentrations are shown in parts per million (ppm), the standard unit for measuring trace gases in the atmosphere. The onset of continental glaciation at ~34 Ma coincided with an atmospheric CO₂ concentration of ~720 ppm.
Chart: Thomas GernonSource: CENCO2PIPGet the dataCreated with Datawrapper