New study reveals how volcanic eruptions and internal climate cycles jointly shape Asian monsoon rainfall

Institute of Atmospheric Physics, Chinese Academy of Sciences

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Major volcanic eruptions inject aerosols into the stratosphere, triggering sea surface temperature changes that can mimic natural climate cycles and reshape monsoon rainfall patterns across Asia.

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Credit: Wenmin Man

From the rice paddies of South Asia to the wheat fields of northern China, summer monsoon rains sustain the livelihoods of billions. Yet these vital rains fluctuate dramatically from decade to decade—a variability that has long puzzled climate scientists.

Now, a study led by Dr. Wenmin Man at the Institute of Atmospheric Physics, Chinese Academy of Sciences, offers new insight into what drives these swings. The research reveals that volcanic eruptions can trigger rainfall patterns remarkably similar to those produced by natural climate variability—effectively "projecting" their influence onto the ocean-driven cycles that scientists have long studied.

Published in Geophysical Research Letters, the findings help untangle a longstanding question: when Asian monsoon rainfall shifts from one decade to the next, are those changes driven by forces outside the climate system—like volcanic aerosols—or by natural oscillations within it?

The answer, it turns out, is both—and the interplay is more complex than previously understood.

Using paleoclimate reconstructions and model simulations covering the past millennium, the research team identified a distinct "tripolar" pattern of summer rainfall variability across Asia. In this pattern, when South Asia gets wetter, Southeast Asia tends to get drier, while northern East Asia's rainfall aligns with South Asia's.

This large-scale pattern, the study confirms, is primarily driven by a natural climate phenomenon known as the Interdecadal Pacific Oscillation (IPO)—a long-lived cousin of El Niño that shuffles heat and moisture across the Pacific Ocean, with ripple effects reaching far into Asia.

But the story doesn't end there. When the team analyzed periods following major volcanic eruptions, they found strikingly similar rainfall patterns emerging. Volcanic aerosols injected into the stratosphere can trigger sea surface temperature changes that resemble an IPO-like pattern, effectively tricking the climate system into producing the same tripolar rainfall response.

"Volcanic forcing can 'project' onto the internal variability mode that naturally drives these precipitation patterns," explains Dr. Man. "This means that even when the IPO itself isn't active, large eruptions can create conditions that mimic its influence on Asian rainfall."

Despite these similarities, the researchers found that volcanic-driven and IPO-driven patterns remain distinguishable—with important implications for both past climate understanding and future planning.

The key difference lies in symmetry. IPO-related temperature anomalies tend to be roughly symmetric around the equator. Volcanic forcing, by contrast, produces a distinctly asymmetric pattern, with cooling more pronounced in one hemisphere depending on the eruption's location and timing.

These subtle but systematic differences provide scientists with a way to tease apart how much of any given decadal shift in Asian rainfall comes from internal variability versus external forcing.

The findings carry particular relevance as scientists explore "climate intervention" strategies—deliberate attempts to cool the planet by injecting aerosols into the stratosphere, mimicking the effects of volcanic eruptions.

"If we're considering stratospheric aerosol injection as a potential tool, we need to understand exactly how such interventions might affect regional rainfall patterns," says Dr. Man. "Our research suggests they wouldn't simply counteract warming uniformly—they'd interact with the climate system in complex ways, potentially amplifying or modifying the natural variability that billions of people depend on for their water supply."

The study was supported by the National Natural Science Foundation of China (Grant No. 42588201).

 

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Journal

Geophysical Research Letters

DOI

10.1029/2025GL118463