In this paper we examine in detail the ''spinup'' of a general circulation model of the atmosphere, initialized with isothermal, dry, calm conditions with a constant surface pressure. The speed at which the spinup occurs depends on the atmospheric parameter and geographical location being examined. What is made clear here are the different thermodynamic and dynamic time scales associated with the problem, these ranging from a few to hundreds of days. A simple analysis suggests the spinup of the atmosphere may not be too different from the atmospheric response to a small perturbation, particularly in tropical regions. The times required for a simple model to readjust to ''small'' changes can be of the order of 6 months or more, in agreement with observational studies. Such long atmospheric time scales may be of considerable importance in explaining interannual variability.