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Massive Volcanic Eruption Impacted Climate, Leaving Humans Unaffected

Research led by Rutgers University reveals that a massive volcanic eruption that occurred in Indonesia around 74,000 years ago was the reason for serious climatic disruptions worldwide; however, early human populations remained unaffected by the terrible effects.

The Rutgers-led researchers examined explosive ash deposits that are tens of meters thick about 35 km north of the Toba caldera in Indonesia. Image Credit: Steve Self, UC Berkeley.

The research findings have been published in the PNAS journal.

Toba volcanic eruption was the biggest volcanic eruption in the past two million years. However, the effects of the eruption on human evolution and climate have been obscure ever since. To understand the environmental changes during the crucial period of human evolution, this controversy has to be resolved.

We were able to use a large number of climate model simulations to resolve what seemed like a paradox. We know this eruption happened and that past climate modeling has suggested the climate consequences could have been severe, but archaeological and paleoclimate records from Africa don’t show such a dramatic response.

Benjamin Black, Study Lead Author and Assistant Professor, Department of Earth and Planetary Sciences, Rutgers University

Our results suggest that we might not have been looking in the right place to see the climate response. Africa and India are relatively sheltered, whereas North America, Europe and Asia bear the brunt of the cooling. One intriguing aspect of this is that Neanderthals and Denisovans were living in Europe and Asia at this time, so our paper suggests evaluating the effects of the Toba eruption on those populations could merit future investigation,” added Black.

The scientists examined 42 global climate model simulations, wherein they assorted time of year of the eruption, magnitude of sulfur emissions, sulfur injection altitude, and background climate state to create a probabilistic assessment of the range of climate disruptions the Toba eruption might have caused. The above approach helped the researchers come out with a few of the unknowns connected to the eruption.

By using a probabilistic approach, we aim at understanding the likelihood that some regions were less impacted by Toba, considering the wide range of estimates of its size and timing, in addition to our lack of knowledge of the underlying climate state.

Benjamin Black, Study Lead Author and Assistant Professor, Department of Earth and Planetary Sciences, Rutgers University

The findings indicated substantial regional variation in climate impacts. The simulations forecast at least 4 °C of cooling in the Northern Hemisphere, while the regional cooling could be as high as 10 °C based on the model parameters.

However, even under the most severe eruption conditions, cooling in the Southern Hemisphere—inclusive of regions inhabited by early humans—was unlikely to surpass 4 °C. But the regions of India and southern Africa could have witnessed reduced precipitation at the highest sulfur emission level.

The findings elucidate independent archaeological evidence that indicates the Toba eruption had moderate effects on the advancement of hominid species in Africa. The ensemble simulation approach put forth by the researchers can be applied to gain better insights into other past and future explosive eruptions.

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 super-eruption underscores the uneven expected distribution of societal and environmental impacts from future very large explosive eruptions,” implies the research.

Journal Reference:

Black, B. A., et al., (2021) Global climate disruption and regional climate shelters after the Toba supereruption. Proceedings of the National Academy of Sciences.


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