Robustness of competing climatic states

TL;DR

This paper investigates the multistability of climate states using the Thermodynamic Diagnostic Tool, analyzing how different steady states vary in their thermodynamic properties and respond to model configuration changes.

Contribution

It applies a novel diagnostic tool to characterize multiple co-existing climate states and assesses the impact of model modifications on these states' thermodynamic signatures.

Findings

Multiple stable climate states can co-exist under the same forcing.

Model configuration changes alter state variables but not the overall attractor.

TheDiaTo effectively quantifies differences between competing climate states.

Abstract

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 until an approximate steady state (or attractor) is reached. However, multiple steady states can co-exist for a given forcing and with the same boundary conditions. Here, we apply the Thermodynamic Diagnostic Tool (TheDiaTo) to investigate the statistical properties of five co-existing climates, ranging from a snowball to an ice-free aquaplanet, obtained in MITgcm coupled simulations. The aim is to explore the multistability of the climate model setup 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. We also investigate how such attractors change when the model configuration is varied. We consider, in particular, the effect of changing the representation of the cloud albedo, and of implementing an improved closure of the energy budget. We find that, even if the dynamics remains on the same attractor, state variables are modified. The set of metrics in TheDiaTo quantifies such modifications and represents a valuable tool for model evaluation.