A brief discussion of the history, strengths and limitations of conceptual climate models for pre-Quaternary time

Although it has been recognized at least since the time of Darwin and Agassiz that climate has varied significantly over geologic time, the study of global palaeoclimate did not come into its own until the theory of continental drift became ascendant. Initial studies in the early 1960s used climate models to test the reconstructions of continental positions. These studies, many collected in a pair of symposium volumes edited by A. E. M. Nairn, used a zonal model of climate or simple modifications thereof to predict how certain palaeoclimatic indicators - principally evaporites, coals, carbonates, red beds, and eolian sandstones - should be distributed on the continents through time if the continental reconstructions were correct. Even at that early stage in the development of continental reconstructions, past patterns of sedimentation were more clearly explained than had previously been the case. Continental reconstructions eventually began to stabilize, at least with respect to the major plates, in the late 1970s. Most of the information for positioning the continents came from paleomagnetic and structural data, but some elements of continental reconstructions relied heavily on climatic data - and the zonal climate model - for positioning. Nevertheless, it was at this time that studies of global palaeoclimate, independent of the concerns about the positions of the continents, could begin in earnest. A primary need was independence of the continental reconstructions from palaeoclimatic data, an ideal even now fully realized only for the late Mesozoic and Cenozoic. The term ‘conceptual climate model’ was coined by J . E. Kutzbach in reference to models published in the early 1980s. Like numerical models, conceptual climate models are based on the fundamentals of atmospheric circulation as determined from studies of the modern climate system, without explicitly treating atmospheric dynamics. They are reproducible and useful for developing an understanding of major changes in climate patterns driven by the changing positions of the continents. Despite their simplicity and non-explicit treatment of atmospheric dynamics, conceptual climate models have proved to be surprisingly robust in that the patterns predicted by explicitly dynamical models are similar for any given geologic period.