MODEL SIMULATIONS OF CRETACEOUS CLIMATES - THE ROLE OF GEOGRAPHY AND CARBON-DIOXIDE

A general circulation model (GENESIS) with seasonally varying solar insolation and a mixed layer ocean is applied to assess the role of continental geometry and increased levels of carbon dioxide to explain the warmth of the Cretaceous period. Model experiments suggest that the role of geography is negligible, in contrast to early model studies with mean annual solar insolation and a simple energy balance ocean. Higher atmospheric carbon dioxide (4 times present) resulted in a 5.5-degrees-C globally averaged surface temperature increase, close to the lower limit required to explain the geologic record. Mid-Cretaceous carbon dioxide concentrations of 4-6 times the present day concentrations are a reasonable explanation of Cretaceous warmth if the GENESIS model provides an accurate estimate of climate sensitivity to geography and carbon dioxide.