Interannual oscillations and sudden shifts in observed and modeled climate

Abstract

It has been proposed that time-dependent synchronization of regional climate oscillations with interannual timescales could create multidecadal climate variability. Tsonis et al. (GRL) modeled the global climate as a coarse-grained network with four nodes: El Niño Southern Oscillation, North Atlantic Oscillation, North Pacific Oscillation, and Pacific Decadal Oscillation, all but the last with significant spectral power at interannual timescales (∼2–7 years). This network seems to synchronize during turning points or “shifts” of multidecadal climate variability in the early 1910s and 1940s and late 1970s and 1990s. This article dissects those results and shows that while the synchronization idea is promising, the original implementation suffers from some issues and requires further modification. We present novel findings of striking irregularity in interannual variability. In climate model simulations, the rising and falling components between local minima and maxima of global annual mean temperature are normally highly correlated, but exhibit significant anticorrelation every 50–80 years. The new results are a step forward in understanding key features of internal climate variability.