Multidecadal Variability of Northern Hemisphere Land Monsoon Precipitation Dominated by Explosive Volcanic Eruptions over the Last Millennium

Volcanic eruptions are among the most profound sources of natural external radiative forcing of the climate system, imparting significant impacts on global and regional climate. Previous studies have established that explosive volcanic forcing induced substantial multidecadal (∼50–70-year timescale) variability in global mean temperature during the last millennium. The consequences for other climate subsystems remain largely unexplored. In this study, volcanic forcing-induced multidecadal variability of the Northern Hemisphere land monsoon (NHLM) and sub-monsoon precipitation is examined through comparison between climate model simulations and speleothem δ18O climate proxy records. We find that volcanic forcing plays a long-term role in modulating the NHLM system and associated precipitation on multidecadal timescales. This variability, however, is consistently found in both proxy records and model simulations, to be intermittent. Volcanic-induced multidecadal variability is observed in the North African monsoon region between 1150 and 1300, while the South Asian monsoon is strongly influenced between 1750 and 1850. In contrast, the East Asian monsoon precipitation exhibits multidecadal variability not directly caused by volcanic eruptions, and the America monsoon region shows no clear volcanic response. These differences can be attributed to the nonlinear, threshold-based responses of sub-monsoon systems to volcanically induced radiative forcing, with responses to weaker forcing indistinguishable from internal variability. Our findings highlight the important, but somewhat complex, linkage between natural volcanic radiative forcing and the response of certain subsystems, such as the NHLM and associated precipitation, to that forcing.