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

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