Response and Fluctuations in Climate Science

The climate is a complex, chaotic, non-equilibrium system featuring a limited horizon of predictability and variability on a vast range of temporal and spatial scales. We show how the Ruelle response theory allows for predicting climate change –  global averages and spatial patterns - using Green functions constructed for comprehensive global climate models. We show how a breakdown of the Ruelle formulas occurs near climatic critical transitions. We find evidence of a clear violation of the fluctuation-dissipation theorem and clarify its theoretical reasons and practical relevance. Finally, we address the problem of climate multistability resulting from the ice-albedo feedback, and find the Melancholia state, i.e. the edge state between the two attractors corresponding to the co-existing warm and snowball climate states. The Melancholia state is the gate for the noise-inducted transitions between the two stable states.