Intermittent multidecadal‐to‐centennial fluctuations dominate global temperature evolution over the last millennium

[1] Observed climate time series covering several centuries are often characterized by fluctuations on multidecadal‐to‐ centennial timescales. These are not homogeneously distributed in time: Instead, they appear within irregularly intermittent temporal intervals, whose irregular duration varies, in general, with the signal fluctuation frequency. A similar irregularly intermittent, frequency‐dependent appearance of energetic fluctuations is found in long‐term Earth system model integrations, consisting of a multi‐ millennia control experiment (i.e., an unforced simulation) and forced simulations covering the last millennium. Here, for the first time, we investigate the long‐term relative importance of internal and externally‐driven variability and their possible interferences on Global Surface Temperature (GST). Multidecadal GST fluctuations are mostly associated to internal variability. Externally‐forced perturbations acting predominantly on centennial timescales tend to overwhelm such variability and to enhance O(∼200 years) GST fluctuations. Externally‐forced perturbations tend also to correspond to major changes in the coherency among internal climate processes, and among them and GST. Citation: Zanchettin, D., A. Rubino, and J. H. Jungclaus (2010), Intermittent multidecadal‐to‐centennial fluctuations dominate global temperature evolution over the last millennium, Geophys. Res. Lett., 37, L14702, doi:10.1029/2010GL043717.