The climatic effects of increased atmospheric CO2 are discussed in the context of the effect upon two basic components of the climate sytem, namely, (1) latitudinal and seasonal radiative heating of the surface-troposphere system and (2) the enhancement of latitudinal and seasonal surface temperatures. Radiative transfer model calculations show that the radiative heating of the surface-troposphere system (caused by increased CO2) undergoes substantial latitudinal and seasonal variations. The seasonal variations are most pronounced at high latitudes. The increased CO2 heating of the surface and troposphere is significantly different for clear sky and overcast sky conditions. These CO2 heating calculations were then incorporated within a seasonal energy balance climate model for the northern hemisphere. Despite the significant seasonal variations in surface-troposphere heating due to increased CO2, the seasonal model results, when annually averaged over all latitudes, yield essentially the same CO2-induced increase in hemispherical mean surface temperature as does an annual energy balance model. The seasonal model, however, shows a strong seasonal variation at high latitudes for the increase in zonal surface temperature due to increased atmospheric CO2. For example, the CO2-induced enhancement in the zonal surface temperature for 80 ¿--90 ¿N is more than 3 times as great in the summer as in the winter.