This study makes use of monthly surface air temperature taken from the long control runs of thirteen coupled atmosphere/ocean general circulation models as well as from the record of observational surface temperature measurements. We examine the mean seasonal cycle as well as the anomaly statistics.

The statistics of the variance of global-mean, two hemispheric-mean, land-mean and ocean-mean surface air temperature first show remarkable differences in our study. The errors are not simply in the magnitude of the variances but even in the phase of the annual harmonic. In some cases a semi-annual harmonic is prominent.

A simple index is defined as a measure of the amplitude of the variance seasonal cycle as indicated by the ratio of January (or February depending on which is larger) variance to July (or August depending on which is smaller) variance. As the different AOGCM control solutions are compared we find that there are considerable differences among the models with regard to this seasonal cycle of variance.

In addition, the model-to-model comparison shows very large qualitative differences in the lag correlation structures.