Saturation in Forcing Efficiency and Temperature Response of Large Volcanic Eruptions

Volcanic eruptions cause climate cooling due to the reflection of solar radiation by emitted and subsequently produced aerosols. The climate effect of an eruption may last for about a decade and is nonlinearly tied to the amount of injected ${\text{SO}}_2$ from the eruption. We investigate the climatic effects of volcanic eruptions, ranging from Mt. Pinatubo-sized events to supereruptions. The study is based on ensemble simulations in the Community Earth System Model Version 2 (CESM2) climate model applying the Whole Atmosphere Community Climate Model Version 6 (WACCM6) atmosphere model, using a coupled ocean and fixed sea surface temperature setting. Our analysis focuses on the impact of different levels of ${\text{SO}}_2$ injections on stratospheric aerosol optical depth (SAOD), effective radiative forcing (ERF), and global mean surface temperature (GMST) anomalies. We uncover a notable time-dependent decrease in aerosol forcing efficiency (ERF normalized by SAOD) for all eruption ${\text{SO}}_2$ levels during the first posteruption year. In addition, it is revealed that the largest eruptions investigated in this study, including several previous supereruption simulations, provide peak ERF anomalies bounded at $-65W{m}^{-2}$. Further, a close linear relationship between peak GMST and ERF effectively bounds the GMST anomaly to, at most, approximately $-10K$. This is consistent across several previous studies using different climate models.