3.2.2 Intermediate complexity models

Like EBMs, EMICs involve some simplifications, but they always include a representation of the Earth’s geography, i.e. they provide more than averages over the whole Earth or large boxes. Secondly, they include many more degrees of freedom than EBMs. As a consequence, the parameters of EMICs cannot easily be adjusted to reproduce the observed characteristics of the climate system, as can be done with some simpler models.

The level of approximation involved in the development of the model varies widely between different EMICs. Some models use a very simple representation of the geography, with a zonally averaged representation of the atmosphere and ocean. A distinction is always made between the Atlantic, Pacific and Indian basins (Fig. 3.4) because of the strong differences between them in the circulation (see section 1.3.2). As the atmospheric and oceanic circulations are fundamentally three-dimensional, some parameterisations of the meridional transport are required. Those developed for EMICs are generally more complex and physically based than the ones employed in 1-D one-dimensional EBMs.

On the other hand, some EMICs include components that are very similar to those developed for GCMs, although a coarser numerical grid is used so that the computations proceed fast enough to allow a large number of relatively long simulations to be run. Some other components are simplified, usually including the atmosphere because this is the component that is most depending on computer time in coupled climate models.

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