Volcanoes are both captivating and disastrous. Most are likely familiar with the common short-term dangers associated with them: explosive forces, lava, and even atmospheric particles disrupting air traffic. But researchers also explore longer-term impacts of eruptions, as their contributions to broader climate patterns are important, but not well understood. For example, it’s known that ejected material can reach high into the atmosphere and cause local or even global cooling to some degree. Assistant Professor Kanon Kino from the Department of Civil Engineering at the University of Tokyo and her international team are now able to connect past tropical volcanic eruptions with historical large-scale droughts across parts of Asia documented over the last millennium.

“A visiting Ph.D. student, Wenzheng Nie, was working on reconstructing Earth's past hydroclimate by using preserved tree-ring patterns,” said Kino. “As tree ring patterns reflect local variations in hydroclimate, we combined existing tree-ring derived data and climate model simulation datasets to reconstruct large-scale hydroclimate variability and atmospheric circulation patterns in the past. When you do this, you can reconstruct atmospheric circulation variability, including remote simultaneous patterns called teleconnections, such as the circumglobal teleconnection (CGT), which is a large-scale atmospheric wave pattern that modulates rainfall across Eurasia. In particular, its negative phase is associated with reduced precipitation over northern East and South Asia. But what surprised us is that drought-causing negative phases of the CGT repeatedly occurred after large tropical volcanic eruptions.”

This relationship does not arise simply from the transport of cooler or drier air. Instead, the key mechanism lies in how volcanic cooling alters atmospheric heating. Large eruptions inject sulfate aerosols into the stratosphere, reducing incoming solar radiation and cooling the surface. This cooling suppresses monsoon convection over South Asia, weakening the release of latent heat into the atmosphere. The reduction in this heating triggers a large-scale atmospheric pattern resembling the negative phase of the CGT. After particularly large eruptions, and depending on other atmospheric conditions, a drought in Asia might occur during the first boreal summer following the eruption. This response is strongest in the first year following a large eruption. This mechanism appears to arise directly from volcanic effects, rather than depending on other climate fluctuations.

“The last negative CGT following a volcanic eruption seemed to take place in the 1960s. And while it could happen again, we now know that the atmospheric response typically peaks in the first boreal summer following a major eruption, it ought to give affected regions time to prepare when it does,” said Kino. “Reconstructing past extreme weather events and understanding the mechanisms is challenging, but climate proxies, such as tree rings, help tackle these problems. I would like to reconstruct more past extreme weather events from even deeper in Earth’s history. I think doing so can help us better understand our changing climate.”