Toward predicting volcanically-forced decadal climate variability

Abstract

Volcanic forcing and climate Strong volcanic eruptions inject into the stratosphere massive amounts of chemically and microphysically active gases that lead to the formation of aerosol particles, affecting the Earth's radiative balance and climate (Robock, 2000; Timmreck, 2012; LeGrande et al., 2016). Sulfate aerosol particles scatter solar radiation back to space, which results in global surface cooling and slowdown of the global hydrological cycle. The particles also absorb radiation in the infrared and near-infrared bands, causing local warming of the lower stratosphere. Both direct radiative forcing effects are temporary, their time scale being set by the persistence of the volcanic aerosol cloud in the lower stratosphere. This amounts

Evidence for a volcanic underpinning of the Atlantic multidecadal oscillation

“…Our synthesis of historical SST, reanalysis, and aerosol optical depth data is in agreement with coupled atmosphere-ocean GCM studies [19][20][21] linking multi-decade SST variability in the North Atlantic to explosive volcanic activity and changes in atmospheric circulation. We find that cool SST anomalies form across the basin in association with NAO+ atmospheric patterns that tend to develop in response to volcanic aerosol loading in the stratosphere.…”

“…The persistence of surface cooling years after a major eruption (or series of eruptions) implies that ocean-atmosphere feedbacks through mixed layer processes are important for maintaining a perturbed climate state. 20,26,28,30 It has been suggested recently that SST declines across the subpolar gyre are symptomatic of an unprecedented AMOC weakening over the past century effected by Arctic melting. 14,31 However, the reported ocean circulation decline occurs mostly over the interval we call VCI-2 (1960s-1990s), which encapsulates the effects of several major volcanic eruptions.…”

“…Other coupled GCM studies indicate that North Atlantic SST variability develops in large part from volcanic aerosol forcing (and to lesser extent solar variability), as explosive eruptions project onto the NAO and elicit ocean response from changes in atmospheric circulation and the distribution of surface winds. 19,20 Coupled GCMs that incorporate robust aerosol-cloud interactions also show that anthropogenic aerosol emissions may have significant impact on SSTs. 21 The volcanic-aerosol framework shares an intuitive basis with studies linking the AMO to the NAO and other wind-related mechanisms.…”

Last Millennium volcanism impact on the South Atlantic Ocean

“…The response of the South Atlantic Ocean, including the Weddell Sea, to volcanic eruptions was evaluated using simulation results from the Last Millennium Ensemble experiment of the Community Earth System Model (CESM-LME). Despite the uncertainties related to complex earth system models (Zanchettin et al, 2017), the use of 15 ensembles and 7 eruptions (a total of 105 events) allowed a solid description of air-sea major impacts and to separate the forced climate response from internal variability (Fasullo et al, 2017). In this sense, this study emphasize the importance of ensemble experiments to reproduce the internal dynamics of the coupled climate system for interpretation of simulated regional past climates (Zanchettin et al, 2012).…”