Using different coupled ocean-atmosphere general circulation models, we study the synoptic variability changes relative to the pre-industrial climate for the cold climatic context of the Last Glacial Maximum (LGM, 21kyrs ago) and for the warm climate associated with CO2 concentration four times higher than for the pre-industrial era. We show that the synoptic variability changes simulated by different models using the same boundary conditions can be very different, but that in all cases, the major changes can be related to the baroclinic conversion term. This term includes the mean horizontal gradient of temperature, but also the ability of the eddies themselves to convert this mean flow energy into eddy energy. The latent heat changes associated with less (more) humidity content in the air under cold (warm) conditions only play a secondary role in terms of their direct effect in the eddy energy budget, but are able to modify the mean temperature gradient and the eddy properties, and hence have an indirect effect on the baroclinic conversion term. The conclusion will include a discussion on different possible future studies.