&gt; That means it has to treat the globe as a grid of 18 mile cubes<p>Although this is made somewhat easier in that the vertical component is done in pressure &quot;levels&quot;, somewhat simplifying the equations to be solved. However that shouldn&#x27;t underestimate the scale of the problem. IIRC a model with a surface resolution of 100km means solving for something of the order of 30 million variables for each time step.<p>Full scale climate models can get even harder, as you need to couple an ocean circulation model to a atmospheric circulation model - ocean circulation is less important for a weather model as its time scale is of the order of up to 1000 years.