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Nonlinearity and Climate Group

Tipping points in the climate system

The first step in exploring the properties of dynamical systems like Earth's climate is to identify the different phase-space regions where trajectories asymptotically evolve, known as attractors or steady-states. Within a given system, multiple attractors can coexist under the influence of the same forcing. At the boundaries of their basins of attraction, the dynamics become highly nonlinear, with small perturbations leading to abrupt and potentially irreversible changes called tipping points, which mark the transition from one attractor to another.

In recent papers, we proved the existence of up to five attractors in an aquaplanet - a planet entirely covered by ocean [1, 2]. These attractors range from a snowball state to a hot state without sea ice. We also investigated three attractors in a more realistic configuration representing Earth's climate around the Permian-Triassic Boundary, approximately 250 million years ago [3]. Currently, we are applying the same approach to other simplified configurations, other geological periods [4, 5] and the present-day climate. In addition, we are developing biogeodynamical tools that make it feasible to run fully coupled climate simulations over multimillennial timescales with reasonable computational costs, enabling a more detailed exploration of Earth's phase diagram.

We are also interested in the question of tipping points and their underlying mechanisms, with a focus on how to characterize their behavior. Recently, we tested Early Warning Signals (EWSs) for detecting such critical points using climate networks [6]. Unlike traditional methods that rely solely on temporal information, these network-based EWSs incorporate both temporal and spatial information via correlation links. We are now planning to enhance these network indicators by considering causal links.

REFERENCES

[1] M. Brunetti, J. Kasparian, C. Vérard, Co-existing climate attractors in a coupled aquaplanet, Climate Dynamics 53, 6293 (2019), 

[2] C. Ragon, V. Lembo, V. Lucarini, C. Vérard, J. Kasparian, M. Brunetti, Robustness of competing climatic states,

[3] C. Ragon, C. Vérard, J. Kasparian, M. Brunetti, Alternative climatic steady states near the Permian-Triassic Boundary,

A poster related to this paper won a BEST POSTER AWARD at the WE-Heraeus Seminar in Templin, Nov. 2023:

[4] M. Brunetti, C. Vérard, P. O. Baumgartner, Modeling the Middle Jurassic ocean circulation,

 with two additional animations of the Jurassic surface currents

[5] M. Brunetti, C. Vérard, How to reduce long-term drift in present-day and deep-time simulations?, Climate Dynamics 50, 4425 (2018), 

[6] L. Moinat, J. Kasparian, M. Brunetti, Tipping detection using climate networks, Chaos 34, 123161 (2024)

A poster related to this paper won a BEST POSTER AWARD at the , April 2024