We used a three-dimensional atmospheric transport model to investigate several aspects of column CO2 that are important for the design of new satellite-based observation systems and for the interpretation of observations collected by Sun-viewing spectrometers. These aspects included the amplitude of the diurnal cycle and how it is related to surface fluxes, the amplitude and phase of the seasonal cycle, and the magnitude of the north-south hemispheric gradient. In our simulation, we found that column CO2 had less variability than surface CO2 on all scales. The annual mean column CO2 north-south gradient and seasonal cycle amplitude were approximately one half of their surface counterparts and the column CO2 diurnal amplitude rarely exceeded 1 ppm. A 1 Gt C yr-1 Northern Hemisphere carbon sink decreased the north-south column CO2 gradient by ~0.4 ppm.