Global energy balance models of the martian atmosphere predict that, for a range of total CO2 inventories, the CO2 atmosphere may condense until a state with a permanent polar cap is reached. This process, which is commonly referred to as atmospheric collapse, may limit the time available for physical and chemical weathering. The global energy balance models that predict atmospheric collapse represent the climate using simplified parameterizations for atmospheric processes such as radiative transfer and atmospheric heat transport. However, a more detailed representation of these atmospheric processes is critical when the atmosphere is near a transition, such as the threshold for collapse. Therefore, we use the Mars Weather Research and Forecasting (MarsWRF) general circulation model (GCM) to investigate how the explicit representation of meridional heat transport and more detailed radiative transfer affects the onset of atmospheric collapse. Using MarsWRF, we find that previous energy balance modeling underestimates the range of CO2 inventories for which the atmosphere collapses and that the obliquity of Mars determines the range of CO2 inventories that can collapse. For a much larger range of CO2 inven- tories than expected, atmospheric heat transport is insufficient to prevent the atmospheric collapse. We show that the condensation of CO2 onto Olympus Mons and adjacent mountains generates a condensa- tion flow. This condensation flow syphons energy that would otherwise be transported poleward, which helps explain the large range of CO2 inventories for which the atmosphere collapses.