Multidecadal climate oscillations during the past millennium driven by volcanic forcing

Past research argues for an internal multidecadal (40- to 60-year) oscillation distinct from climate noise. Recent studies have claimed that this so-termed Atlantic Multidecadal Oscillation 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 preindustrial era. By comparing control and forced Last Millennium simulations, we show that these apparent multidecadal oscillations are an artifact of pulses of volcanic activity during the preindustrial era that project markedly onto the multidecadal (50- to 70-year) frequency band. We conclude that there is no compelling evidence for internal multidecadal oscillations in the climate system.

Automated summary

Research suggests that the Atlantic Multidecadal Oscillation may actually be influenced by competing effects of anthropogenic greenhouse gases and sulfate aerosols, rather than being an internal climate oscillation. By comparing climate model simulations and paleoclimate data, it is concluded that the apparent multidecadal oscillations are likely artifacts of volcanic activity during the preindustrial era, projecting onto the 50- to 70-year frequency band. Thus, there is currently no compelling evidence for internal multidecadal oscillations in the climate system.