evidence: The geochemistry here is quite involved, and I’m not qualified to assess how well this has been done, but it’s sufficient to take this as perfectly valid for the points I’ll make here. There are often somewhat heroic assumptions made in deriving paleo atmospheric CO2 from molecular markers, but the overall results (see left hand figure) – that CO2 went from 650 ppm 15 Million years ago (Ma) to 280 ppm in the most recent data point (close to the long term pre-industrial average), is not dramatically different from other recent compilations (such as CenCO2PIP (2023)) (right hand figure). The novelty here is (I think) that this change is calculated in a single core over the whole 15 Ma interval (albeit at a roughly 500,000 yr sampling interval).