Steady states and bifurcation diagram for the Permian-Triassic paleogeography

The climate relaxes toward a steady state under a permanent inhomogeneous forcing from solar radiation and dissipative mechanisms. As a highly nonlinear system, the Earth’s climate can exhibit multiple steady states at a given forcing. Multistability has been observed in numerical models of different complexities, including fully coupled general circulation models with an aquaplanet configuration (Ragon et al. 2022), and we show here multistability also applies for the Earth in deep time.

We use the MIT general circulation model in a coupled atmosphere-ocean-sea ice-land configuration to perform simulations at a constant forcing i.e., fixed solar constant and atmospheric partial pressure of CO2. We let the system relax for thousands of years, which is the typical timescale of ocean dynamics. Considering the paleogeography of the Permian-Triassic reconstructed after PANALESIS (Vérard 2015), we find multiple competing steady states, representing alternative potential climates for that period.

Then, we construct the corresponding bifurcation diagram by varying the atmospheric CO2 content. This allows us to identify the stability range of each steady state, the position of tipping points and the required conditions for the system to shift from one state to another, which may help to understand the climatic oscillations observed, e.g., during the Early Triassic.

References

Ragon C., Lembo V., Lucarini V., Vérard C., Kasparian J. & Brunetti M., Robustness of competing climatic states. Journal of Climate, 35, 2769-2784. (2022)

Vérard C., PANALESIS: Towards global synthetic palæogeographies using integration and coupling of manifold models. Geological Magazine, 156, 320-330. (2015)