Climate Variability Across Scales: from centuries to millennia (CVAS)

"Weather is what you get, climate is what you expect". Is it, really? Consider a series of measurements of temperature along the time axis (Fig. 1A). If successive fluctuations tend to cancel each other (Fig. 1B), then averaging over longer and longer intervals smooths the signal; the averages converge more and more to an (apparently) well-defined mean value. However, if slow processes are forcing the system for example changing the albedo or CO2 the system changes constantly, so that this apparently convergent mean slowly varies, and choosing longer and longer periods to estimate it will be of no help. such systems "wander"; they do not "relax" (Fig. 1C). Whether the system is relaxing or wandering is a matter of timescales: at weather scales or at the multi-millennium (climate) scales, it wanders. Predicting the future thus requires knowledge of the entire history of the evolution of the system.