Seasonal and interannual variations of the clear-sky greenhouse effect (G) are analysed for 10 general circulation models (GCMs) participating in the atmospheric model intercomparison project (AMIP). Results are compared to ERBE observations between 1985 and 1988. In order to trace the source of G variability, we also study modelled variability of the precipitable water content (W) and compare the results to ISCCP/TOVS and SSM/I estimates. For a subset of models, the variability of temperature and water vapor profiles are also examined and compared to ECMWF analyses and NCEP/NCAR reanalyses for the year 1988. Large differences between models and a bias relative to observations are pointed out for annual mean values of W and G as well as for their seasonal and interannual variabilities. The model discrepancies are larger in the tropics. In these regions, there is a dry bias in all the GCMs considered relative to both ISCCP/TOVS and SSM/I and factors of 2 or 3 are found in the variability of G and W compared to observations. The GCMs considered tend to overestimate the seasonal variation of G in middle latitudes and to underestimate it in the tropics. The opposite is found for interannual variations. Inspection of vertical temperature and relative humidity profiles reveals that the origin of the clear-sky greenhouse effect variability can be very different from one model to another.