Robustness of competing climatic states.

The climate is a non-equilibrium system undergoing the continuous action of forcing and dissipation. Under the effect of a spatially inhomogeneous absorption of solar energy, all the climate components dynamically respond by redistributing energy until an approximate steady state is reached. In order to improve the skill of climate models and correct their biases, it is essential to investigate how such dynamical balance is reached. In general, the climate system features multiple steady states for a given set of boundary conditions. Here, we apply the Thermodynamic Diagnostic Tool (TheDiaTo) to investigate the statistical properties of the five co-existing climates, ranging from a snowball to an ice-free aquaplanet, obtained in MITgcm coupled simulations under the same boundary conditions. The aim is to explore the multistability of the climate by highlighting differences in competing steady states and their characteristic signatures regarding the meridional transport of heat and water mass, the Lorenz energy cycle and the material entropy production. Alternative cloud parametrizations and descriptions of energy exchange are also used to investigate how robust such signatures are and, at the same time, how the statistical properties can be improved in the simulated climatic states. Thus we show how the diagnostic tool can help in identifying strengths and weaknesses of a model configuration.