When Stabilizing Feedbacks Wreak Havoc in Habitable Planets: Chaos at the Freezing Point in a Four-Feedback Climate Model

Abstract

The long-term habitability of Earth-like planets is governed by the balance of positive and negative climate feedbacks that regulate surface temperature and atmospheric composition. While some feedbacks, such as ice-albedo and silicate weathering, are thought to operate on many terrestrial planets, the number and strength of additional climate feedbacks may vary substantially from world to world. An important open question is whether and how the introduction of an additional climate feedback influences long-term climate evolution and complexity. To investigate this question, we extended a low-order climate model including outgoing longwave radiation, ice--albedo, and carbonate--silicate weathering, with an additional generalized feedback. Across 35,864 simulations, we characterized dynamical behavior using the largest Lyapunov exponent (LLE). While 10.4% of explored parameter combinations exhibited positive LLEs, indicating chaos, the fraction rose to 25.6% within the stabilizing, near-freezing regime. This suggests that chaotic behavior is preferentially concentrated where a strong stabilizing feedback operates in the same temperature regime as a strong destabilizing feedback, contrary to the expectation that additional negative feedbacks should increase climate stability. Increasing normalized volcanic outgassing shifts the chaotic regime toward lower stellar flux and partially suppresses chaos at high instellation.