Nonlinear mechanism of climatic variability

At timescales greater than 10³ years, Earth's climate exhibits intermittent bursts of carbon dioxide and warming followed by periods of relative quiescence. Identifying what instigates and damps these disruptions remains enigmatic. At high frequencies, fluctuations exhibit a Laplacian (double-exponential) distribution, whereas at low frequencies the fluctuations are Gaussian. Here we show that a constant-rate, thermostatic feedback operating at a hierarchy of scales predicts this transition. Using our model, we derive a fluctuation-dissipation relation from which we extract damping constants and rates of observed fluctuations, including their distribution over time. From the latter, we successfully predict the shape of the observed power spectrum. These results show that a symmetric, saturating feedback suffices to explain quantitative and qualitative aspects of climatic variability. Even though the thermostatic feedback is negative, its operation at multiple scales acts to amplify external perturbations.