The role of geographic variables in explaining paleoclimates: Results from Cretaceous climate model sensitivity studies

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Abstract
Changes in geography (topography, continental positions and sea level) are one of the most frequently cited mechanisms of climatic change on geologic time scales. The role of geographic variables in paleoclimatology is investigated through a series of climate model sensitivity studies using a version of the National Center for Atmospheric Research spectral GCM and specified Cretaceous (≈ 100 million years ago) geography. The Cretaceous is investigated because it was both a large geographic and climatic contrast from the present day. The model simulations demonstrate that paleogeography was a substantial climatic forcing factor (4.8°K increase in globally averaged surface temperature compared with a present‐day control). However, the warming is insufficient to explain fully the paleoclimatic data. In addition, the model is insensitive to global sea level variations (related to tectonics and not ice volume) which are well correlated with paleoclimatic data. Additional climatic forcing factors, such as increased atmospheric CO2 correlated with these sea level variations, may be required to explain the Cretaceous climate.