A Case for a New Step in the Model Hierarchy: The Impact of Convective Parameterization on the Circulation Response to Global Warming in a Model of an Idealized Moist Atmosphere (MiMA)

The accurate projection of regional-scale changes in temperatures and precipitation is essential for estimating the potential cost of climate change. Comprehensive climate models struggle to robustly project the regional responses of these quantities to anthropogenic forcing, especially over land. There is considerable spread across models, even if one accounts for differences in their climate sensitivity. The key difficulty is that regional-scale weather is highly sensitive to changes in the large-scale circulation of the atmosphere, which is in turn sensitive to the representation of unresolved (parameterized) processes.

Here, a new intermediate-complexity atmospheric model is developed to allow for the exploration of the interaction between resolved and parameterized convection with the large scale circulation. The chief simplification is to exclude cloud-radiation feedbacks. While this limits the complexity (and so realism) of the model, it allows for a more systematic exploration of the role of convective parameterization in the response to global warming. In particular, by controlling for the impact of convective parameterization on the climatological state of the model, we can more effectively isolate its role in the expansion of the Hadley Cell and poleward shifts of the extratropical jet streams in response to CO2.