Climate models have now reached a third generation of variants. They have, in the more than one century of iterations that have taken place, added a considerable level of sophistication to the original approaches. Models now attempt customarily to explain the entire global system instead of regional or partial attempts, owing to the greater level of understanding of the heterogeneity of interactions around the world.
Nevertheless, the basic approach remains the same, in that the atmosphere is divided both vertically and horizontally into sections. This entails dividing the surface of the earth into a series of two-dimensional squares that are then provided with a three-dimensional element of height. Early models posited a homogeneous surface cover that was a composite of land and water. Subsequently, grid squares have been accurately divided into those areas which are land and which are sea, together with possible layers of ice with an additional variable concerning land cover. Degrees of salinity and the exchange of salt between land and sea ice have also been integrated, as have up to several dozen vertical layers of the atmosphere. The models themselves are divided into three principal component areas; the land, the sea (and the ice), and the atmosphere. To make improvements more feasible, researchers will tend to work on one of these component areas individually, although this is not required.
Climate modelers create their own individual models, which are similar in basic approach but vary in the forcings, or weighting given to specific variables within the model. The different weightings, like variations within the initial conditions ascribed to the model, will produce often significant changes in predictions, especially over the long-term if variations become magnified with regular, perhaps annual, increases in the relevant variables concerned. Consequently, it is prudent to run a series of simulations with marginally different initial conditions and forcings to consider possible outlying results.
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