Global climate disruption and regional climate shelters after the Toba supereruption

Significance The Younger Toba Tuff is the largest volcanic eruption of the past 2 million years, but its climatic consequences have been strongly debated. Resolving this debate is important for understanding environmental changes during a key interval in human evolution. This work uses a large ensemble of global climate model simulations to demonstrate that the climate response to Toba was likely to be pronounced in Europe, North America, and central Asia but muted in the Southern Hemisphere. Our results reconcile the simulated distribution of climate impacts from the eruption with paleoclimate and archaeological records. This probabilistic view of climate disruption from Earth’s most recent supereruption underscores the uneven expected distribution of societal and environmental impacts from future very large explosive eruptions. The Toba eruption ∼74,000 y ago was the largest volcanic eruption since the start of the Pleistocene and represents an important test case for understanding the effects of large explosive eruptions on climate and ecosystems. However, the magnitude and repercussions of climatic changes driven by the eruption are strongly debated. High-resolution paleoclimate and archaeological records from Africa find little evidence for the disruption of climate or human activity in the wake of the eruption in contrast with a controversial link with a bottleneck in human evolution and climate model simulations predicting strong volcanic cooling for up to a decade after a Toba-scale eruption. Here, we use a large ensemble of high-resolution Community Earth System Model (CESM1.3) simulations to reconcile climate model predictions with paleoclimate records, accounting for uncertainties in the magnitude of Toba sulfur emissions with high and low emission scenarios. We find a near-zero probability of annual mean surface temperature anomalies exceeding 4 °C in most of Africa in contrast with near 100% probabilities of cooling this severe in Asia and North America for the high sulfur emission case. The likelihood of strong decreases in precipitation is low in most of Africa. Therefore, even Toba sulfur release at the upper range of plausible estimates remains consistent with the muted response in Africa indicated by paleoclimate proxies. Our results provide a probabilistic view of the uneven patterns of volcanic climate disruption during a crucial interval in human evolution, with implications for understanding the range of environmental impacts from past and future supereruptions.