claim: The killer proof that CO2 does not drive climate is to be found during the Ordovician- Silurian and the Jurassic-Cretaceous periods when CO2 levels were greater than 4000 ppmv ( parts per million by volume ) and about 2000 ppmv respectively.
evidence: The Devonian (  / dɪˈvoʊn.i.ən, də-, dɛ- /  dih-VOH-nee-ən, də-, deh- ) is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago ( Mya ), to the beginning of the Carboniferous, 358.9 Mya.