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Abstract

The most complex climate models are general circulation models (GCMs) of the atmosphere and the ocean. The structure of the state-of-art GCMs is described. The complexity of a GCM originates, to a large extent, from the representation of the forcing terms in the underlying equations. These terms involve small-scale or even molecular-scale processes. It is shown that fluctuations produced by these processes supply the slow climate components with energy through non-linear processes. As a consequence, the variability behavior in an integration with a complex model that represents these small-scale processes is generally different from that in an integration with a simple model that neglects these processes.