Tonga’s Eruption Punched Into the Edge of Space. The Stratosphere Cooled, and It Still Has Not Recovered

Hunga Tonga eruption

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Summary: ‘Scientists spent three years figuring out why this volcano did the opposite of everything they predicted.’ — Stratospheric cooling is usually linked in climate theory to atmospheric warming, but this eruption had its own characteristics, one being longer-lasting effects than other volcanoes.
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On January 15, 2022, a volcano on the floor of the South Pacific exploded with enough force to punch a plume 35 miles into the sky, says the Daily Galaxy.

Scientists expected the usual aftermath: sulfur aerosols drifting upward, the stratosphere warming slightly, surface temperatures dipping for a year or two.

Instead, the atmosphere cooled in a layer where it was supposed to warm, and three years of international research were needed to explain why.

A new scientific assessment confirmed that the Hunga Tonga-Hunga Haʻapai eruption chilled the stratosphere rather than heated it, left no measurable fingerprint on the record global temperatures of 2023 and 2024, and drove more water into the upper atmosphere than any eruption scientists have been able to measure.

The figure at the center of the story is 146 teragrams, the mass of water vapor the eruption delivered to the stratosphere. That equals 10 percent of all the moisture already sitting in that atmospheric layer.

According to a study led by atmospheric scientist Luis Millán at NASA’s Jet Propulsion Laboratory, published in Geophysical Research Letters, the total was nearly four times the water contribution of the 1991 Mount Pinatubo eruption, which had been the modern benchmark for volcanic atmospheric disruption.

Why the Caldera’s Depth Changed Everything
Nearly every unusual feature of this eruption traces to one fact: the Hunga caldera sat 490 feet below the ocean surface. That depth placed it in a narrow physical window. Deep enough for erupting magma to superheat vast volumes of seawater into vapor. Shallow enough that ocean pressure could not muffle the explosion. A few hundred feet in either direction and the eruption likely unfolds as an ordinary event.
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Water Vapor Radiates Heat Out. It Does Not Hold It In.
This is the core of why the eruption defied expectations. Sulfate aerosols act like a lid, trapping solar energy inside the stratosphere and raising its temperature. Water vapor behaves the opposite way: at high altitude it emits heat back toward space, pulling energy out of the layer rather than concentrating it.

The result was stratospheric cooling of 0.5 to 1 degree Celsius across broad regions of the upper atmosphere, according to the assessment. Researchers at the University of Colorado Boulder described this as behavior with no clear parallel in the modern eruption record. At ground level, the effect was barely detectable, a surface temperature shift of around 0.05 degrees Celsius. Pinatubo, by comparison, cooled the surface by 0.25 to 0.5 degrees.
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Three Years Later, the Signal Is Still There
As of late 2025, stratospheric water vapor levels from the eruption remain above normal. Dr. Sandip Dhomse of the University of Leeds said the elevated moisture is expected to linger for several more years, a longer atmospheric footprint than sulfate-driven eruptions typically leave. Across parts of the Southern Hemisphere, short-term ozone losses were detected in the months after the eruption, linked to shifts in air circulation rather than direct chemical breakdown of ozone molecules.

Full article here.
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Image: Hunga Tonga eruption