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 Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago ( Mya ) to the start of the Silurian Period 443.8 Mya.