This paper describes a simple global climate model useful in a freshman or sophomore level course in climatology. There are three parts to the paper. The first part describes the model, which is a global model of surface air temperature averaged over latitude and longitude. Samples of the types of calculations performed in the model are provided. The second part of the paper discusses the computer code. The model is coded in Fortran-77 and requires about 45K bytes of storage in executable form. It can, therefore, be run on almost any machine. Part three discusses how the model can be used to illustrate several features of the global energy balance. Students might be asked to invent a scenario and investigate the climatic consequences. Or the model can illustrate concepts such as equilibrium, relaxation time and thermal inertia, positive and negative feedbacks, and stability. Among the virtues of this model are its small size, its robustness to user abuse, and its ability to illustrate at least qualitatively a large number of features of global climate. (RM)