Modelling atmospheric CO2 changes at geological time scales

By trapping infrared radiation, atmospheric CO2 contributes significantly to the greenhouse warming of the planetary surface. Hence, it is thought to have played a key role in the evolution of the Earth's climate over geological time. The history of atmospheric CO2 is available only for the last few hundred thousand years from the analysis of the air trapped in cores of ice. Therefore, data regarding Pre-Pleistocene atmospheric CO2 must be derived from proxies. These provide indirect estimates of atmospheric CO2 and are much less reliable than ice-core data. The main proxies used to reconstruct atmospheric CO2 are: the 13C isotopic fractionation of marine organisms, the paleo-pH recorded in the boron isotopic composition of ancient carbonates, the stomatal density of fossil leaves and the 13C isotopic composition of paleosols.