Comments on the BLAG model; Factors affecting atmospheric CO 2 and temperature over the past 100 million years

Abstract

Since publication of the BLAG model, several new items have appeared that bear on the question of paleo-atmospheric CO ~2~ levels. First, there is a problem between recent estimates in the literature of Cretaceous sea-floor spreading rates being similar to today and many reports of much more abundant Cretaceous volcanism. Second, the temperature dependence of weathering assumed in the BLAG model is in agreement with present data on the relation between temperature and average riverine silica concentrations. Third, increased worldwide organic carbon burial rates and increased land volcanism during the Cretaceous can be used to infer increased CO ~2~ uptake via rock weathering at that time. Finally, new model calculations show that the simple extrapolations of the BLAG model give a paleotemperature-versus-CO ~2~ relation that is in agreement with the new model results within the probable error of paleotemperature estimates.\--Modified journal abstract.