As detailed in Chapter 19, are viewed as comming from a hierarchy of atmospheric models: the simplest of which are datasets of varying complexity and the most complicated ones are the GCM's. The following is a summary of the various options relating to with further details being left to Chapter 19. One and only one option of the following options must be enabled: simple_sbc, time_mean_sbc_data, time_varying_sbc_data, or coupled.