Centennial Variability

Centennial variability is climate variation on timescales of roughly a century, longer than decadal modes such as the PDO but shorter than the orbital pacing of glacial cycles. It arises from slow ocean-circulation adjustments, integrated stochastic atmospheric forcing, and external forcing from volcanic aerosols and solar output. The Atlantic overturning circulation carries memory on these timescales, so subpolar North Atlantic SST shows century-scale swings. Centennial signals are hard to separate from forced trends in the short instrumental record, so paleoclimate proxies (corals, sediment cores, ice cores) supply the long context.