Estimating the role of natural variability in climate change using observations

Large ensembles of climate change simulations provide valuable insight into the role of natural variability in climate change. But they are invariably computationally expensive. In this work we develop a simple analytic expression for the role of natural variability in climate change. The results suggest that the signature of natural variability in future climate can be quantified with a high degree of accuracy from two simple statistics, both of which can be derived from either a control simulation or the observations: the autocorrelation and standard deviation of the unforced variability. The results suggest that the signature of natural variability in future climate can be deduced with a high degree of fidelity from the statistics of the observed climate.