Decadal Variability of Interacting Climate Subsystems in the Northern Hemisphere

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Improved understanding of Northern Hemisphere decadal climate variability is an issue of tremendous societal importance. The goal of this project is to document simulated decadal variability and to analyze the dynamics of decadal climate shifts in global climate model simulations. Using a novel hybrid dynamical/statistical modeling framework to study the dynamics of the decadal climate shifts and relate them to climate processes operating on shorter, intraseasonal-to-interannual time scales, this work will shed insights into how various components of the climate system interact. The researchers hypothesize that decadal climate shifts - defined as abrupt changes in the climates long-term state and variability that tend to happen with decadal frequency - arise as a result of collective behavior of climate subsystems due to interplay between occurrences of synchronized states and variable coupling strength within the climate network. This mechanism, which is consistent with the theory of synchronized chaos, appears to be a very robust mechanism operating in the climate system. It has been found in instrumental records, in forced and unforced climate simulations, as well as in proxy records spanning several centuries. The tendency for the climate subsystems to synchronize/couple their intra-seasonal 'beats' appears to be enhanced in certain phases of the slowly varying Meridional Overturning Circulation in the Atlantic (AMOC), which is dominated by the decadal time scales. This work will thus provide quantitative estimates of climate predictability in the Northern Hemisphere associated with the coupled climate subsystems simulated by comprehensive climate models.