Shifts in Asian Rainfall Tied to Major Volcanic Eruptions

Over the past 800 years, large volcanic eruptions have led to significant shifts in Asian monsoons, altering rainfall patterns in ways that were the opposite of what many climate models have predicted, according to a study by Columbia University scientists. Using tree ring data from 300 sites across Asia to measure the effects of 54 eruptions over the last 800 years, the researchers found that large eruptions actually led to increased rainfall in Southeast Asian countries including Vietnam, Laos, Cambodia, Thailand, and Myanmar. Climate models had predicted that sulfate aerosols from volcanic eruptions would deflect solar radiation and cool the Earth, leading to less surface water evaporation and lower rainfall. And that was indeed the case in large parts of Central Asia, southern China and Mongolia, according to tree ring data. But the exact opposite happened in Southeast Asia, where the years immediately after large eruptions saw increased rainfall, according to the study, published in Geophysical Research Letters. The researchers at Columbia’s Lamont-Doherty Earth Observatory said it is still unclear why this is so, although one possible reason is the impact of strong El Nino weather cycles that might counteract the effects of the eruptions.