2000 Articles

Solving problems with GCMs: General circulation models and their role in the climate modeling hierarchy

Robertson, Andrew W.; Ghil, Michael

We outline the familiar concept of a hierarchy of models for solving problems in climate dynamics. General circulation models (GCMs) occupy a special position at the apex of this hierarchy, and provide the main link between basic concepts—best captured by very simple, "toy" models—and the incomplete and inaccurate observations of climate variability in space and time. We illustrate this role of GCMs in addressing the problems of climate variability on three time scales: intraseasonal, seasonal-to-interannual, and interdecadal. The problems involved require the use of atmospheric, oceanic, and coupled ocean-atmosphere GCMs. We emphasize the role of dynamical systems theory in communicating between the rungs of the modeling hierarchy—toy models, intermediate ones, and GCMs—and between modeling results and observations.