It is a well accepted rule not to interpret the results of a numerical model at space scales smaller than about four times the resolution of the numerical scheme. Therefore a global climate model with 200 km horizontal resolution can only give information at scales of about 1000 km. If climate change information at scales below 1000 km is sought regional models have to be nested into global models. As obvious from figure 3.9 even double nesting is used in recent years to project climate change to scales of about 10 km.
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