Three basic problems of paleoclimatic modeling: a personal perspective and review

The development of a theory of the evolution of the climate of the earth over millions of years can be subdivided into three fundamental, nested, problems: Firstly, to establish by equilibrium climate models (e.g., general circulation models) the diagnostic relations, valid at any time, between the fast-response climate variables (i.e., the weather statistics) and both the prescribed external radiative forcing and the prescribed distribution of the slow-response variables (e.g., the ice sheets and shelves, the deep ocean state, and the atmospheric CO₂ concentration). Secondly, to construct, by an essentially inductive process, a model of the time-dependent evolution of the slow-response climatic variables over time scales longer than the damping times of these variables but shorter than the time scale of ultra-slow tectonic and astronomical changes in the boundary conditions (e.g., altered geography and elevation of the continents, slow outgassing and weathering and and solar radiative output). Thirdly, to determine the nature of these ultra-slow processes and their effects on the evolution of the equilibrium state of the climatic system about which the previously mentioned time-dependent variations occur. In this review we discuss the basis for this resolution, and give a broad overview of the contributions that have been made thus far in each area, emphasizing the work of the Yale climate group.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil