One Curious Thing

No. 034 MON 02 NOV 2026

No. 034 MON 02 NOV 2026

Hunga Tonga cooled one sky layer, warmed the next.

Hunga Tonga eruption — Tonga

A May 20, 2025 study found that the 2022 Hunga Tonga blast sent so much water high up that it pulled the middle sky a few degrees cooler for over a year. The same water sped the growth of large sulfate particles that drifted downward and delivered over half of a slight, one‑to‑two‑degree warming in the layer below. Independent assessments report the extra stratospheric water was still present in 2025.

Why it’s interesting

Fig. 034 Upper waves show strong cooling from added water; the lower ring and black wedge mark that large particles accounted for over half of the slight warming below.

Why it’s interesting

It shows that a water‑rich volcano can tug the stratosphere in opposite directions at once—cooling high above while nudging warmth into the layer below—and leave a fingerprint that lingers. It also reframes eruptions: water can matter as much as sulfur.

ISS view of the Hunga Tonga eruption plume over the South Pacific, January 2022.

Hunga Tonga–Hunga Ha’apai’s massive eruption plume seen from the International Space Station in January 2022—an illustrative view of material injected into the stratosphere that scientists link to lingering water vapor and aerosol changes.

Photo: NASA Earth Observatory · Public domain. Cropped in social posts.

The longer version

On May 20, 2025, researchers reported that the January 2022 Hunga Tonga eruption lofted so much water into the stratosphere that it split the temperature response by height. High in that region, the added water radiated heat to space and drove a marked chill—up to about four degrees—lasting well over a year, while aerosol heating there was small.

The same water accelerated sulfur chemistry and gas‑to‑particle growth, creating unusually large sulfate droplets that drifted downward. There, their sunlight absorption explained more than half of a gentle one‑to‑two‑degree warming that emerged by mid‑2022. An international 2025 assessment, echoed by NOAA, found that the global stratosphere still held roughly a tenth more water than usual through 2025, matching the observed cooling patterns.

Edition
No. 034
Date
Monday 2 November 2026
Subject
Hunga Tonga eruption
Locality
Tonga
Period
2022–2025
Field
earth
Evidence
4 sources, 2 primary

See how we got here

Found after 35 research paths · Selected from 6 candidates

  1. 01 Volcanoes and climate Big blasts can alter sunlight and heat high above us.
  2. 02 Stratospheric water Hunga Tonga sent an unprecedented pulse of water aloft.
  3. 03 Radiative cooling aloft The water‑rich layer ran a few degrees cooler for over a year.
  4. 04 Sulfate particle growth Water sped gas‑to‑particle conversion, making unusually large droplets.
  5. 05 Layered temperature response Warmth appeared lower down as big particles absorbed sunlight.
  6. 06 Hunga Tonga 2022 signal Independent reports saw the extra water lingering into 2025.
  7. → Hunga Tonga cooled one sky layer, warmed the next.

Sources

Nothing publishes without independent sources. How we verify →

  1. 1
    Impact of water vapor on stratospheric temperature after the 2022 Hunga Tonga eruption: direct radiative cooling versus indirect warming by facilitating large particle formation

    Nature Portfolio (npj Climate and Atmospheric Science) · 2025 · peer reviewed Primary

    Quantifies −4 K mid‑stratospheric cooling; ~1–2 K lower‑stratospheric warming; >60% WV contribution to mid‑stratospheric ΔT; >50% aerosol contribution to lower‑stratospheric ΔT; WV‑enabled rapid sulfate particle growth via gas‑to‑particle conversion.

    nature.com

  2. 2
    Impact of Water Vapor on Stratospheric Temperature After the 2022 Hunga Tonga Eruption: Direct Radiative Cooling Versus Indirect Warming By Facilitating Large Particle Formation (accepted manuscript record)

    NASA Technical Reports Server (NTRS) · 2025 · government Primary

    States that condensation and nucleation processes facilitated by abundant WV accounted for ~90% of observed particle radius growth; mid‑stratospheric cooling up to −4 K with >60% attributed to WV; ~50% of the 1–2 K lower‑stratospheric warming attributed to heating by large particles.

    ntrs.nasa.gov

  3. 3
    International Report on the Global Atmospheric Impacts of the 2022 Hunga Volcano Eruption (press summary)

    World Climate Research Programme (WCRP) · 2025 · scientific organization

    Reports ~10% increase in global stratospheric water vapor still present in 2025; documents stratospheric cooling patterns consistent with water‑rich Hunga forcing.

    wcrp-climate.org

  4. 4
    International Report Unveils the Global Atmospheric Impacts of the 2022 Hunga Volcano Eruption

    NOAA Chemical Sciences Laboratory · 2025 · government

    Independent summary confirming that much of the ~10% SWV increase remained through 2025 and describing associated stratospheric cooling magnitudes.

    csl.noaa.gov

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