Supplementary data, code, and information for ‘Multidecadal climate oscillations during the past millennium driven by volcanic forcing’ (Science, Mann et al. 2021)

Past research argues for an internal multidecadal (40-60 year) oscillation distinct from climate noise. Recent studies have argued this so-termed Atlantic Multidecadal Oscillation (“AMO”) is instead a manifestation of competing time-varying effects of anthropogenic greenhouse gases and sulfate aerosols. That conclusion is bolstered by the absence of robust multidecadal climate oscillations in control simulations of current-generation models. Paleoclimate data, however, do demonstrate multidecadal oscillatory behavior during the pre-industrial era. Comparing control and forced “last millennium” simulations, we show that these apparent multidecadal oscillations are an artifact of pulses of volcanic activity during the pre-industrial era that project significantly onto the multidecadal (50-70 year) frequency band. We conclude that there is no compelling evidence for internal multidecadal oscillations in the climate system.