Constructing a climate model

Construction of a climate model is a task whose principles are easily understood but which in practice involves mastery of a multitude of technical details. In this chapter we thus present the generalities in this first section, while an introduction to the more quantitative aspects is given in subsequent sections. A reader who is interested primarily in the output of climate models or in an overview of their construction can thus restrict their attention to section 5.1, skipping the more detailed material of sections 5.2 through 5.4. Section 5.5, which introduces issues of model climate equilibration and errors, is useful background for Chapter 7, and section 5.6 provides a sense of how well models simulate current climate.

The climate models discussed in section 5.1 are the general circulation models (GCMs). Other types of climate models are summarized in section 5.4, along with models that are relevant to climate studies such as weather prediction models, atmospheric regional models and cloud resolving models. Many of the principles used are the same as for the GCMs, each type of model having a particular aim that leads to variations within the same overall modeling approach.

For computational representation, the continuous fields of temperature, pressure, velocity, etc. in the atmosphere and ocean must be approximated by a finite number of discrete values. The most intuitive approach to this discretization is to divide the fluid up into a number of grid cells and approximate the continuous field by the average value across the grid cell or the value at the center of the grid cell.