On January 15, 2022, the underwater volcano Hunga Tonga-Hunga Ha‘apai erupted violently in the South Pacific. It injected an unprecedented amount of water vapor directly into the stratosphere — roughly 146 to 160 million metric tons (teragrams), boosting total stratospheric water vapor levels by about 10%.
Hunga Tonga is still affecting the atmosphere.
— Electroverse (@Electroversenet) June 23, 2026
On Jan 15, 2022, the underwater volcano erupted in the South Pacific. It blasted roughly 160 million metric tons of water vapor into the stratosphere, increasing levels by an unprecedented 10%.
Most major eruptions cool the planet… pic.twitter.com/hjjrq5DYVZ
This was no ordinary volcanic event. Most major eruptions, like Mount Pinatubo in 1991, cool the planet by lofting sulfur dioxide that forms reflective sulfate aerosols, which scatter sunlight back to space. Hunga Tonga, being submarine, punched seawater high into the atmosphere instead. The result was a massive plume of water vapor with comparatively little cooling aerosol.
Water vapor is Earth’s dominant greenhouse gas — responsible for the majority of the natural greenhouse effect. NASA scientists noted immediately that the eruption “could end up temporarily warming Earth’s surface” because the added water vapor traps heat.
The 2023-2024 Temperature Spike
Global temperatures rose sharply in 2023 and reached record levels in 2024. Mainstream narratives attributed this almost entirely to accelerating CO₂-driven warming, often downplaying or dismissing any role for the Hunga Tonga eruption.
Yet the timing aligned precisely with the volcanic injection. Satellite data from NASA’s Aura Microwave Limb Sounder (MLS) showed the stratospheric water vapor burden jump dramatically after January 2022 and remain elevated for years. This extra water vapor acted as a potent, temporary greenhouse forcing in the upper atmosphere.
Independent temperature records, including lower-troposphere satellite data, captured the spike clearly. The anomaly climbed notably through 2023–2024 before showing signs of reversal.
The Reversal Is Now Underway
The key test has arrived. Stratospheric water vapor does not stay elevated indefinitely. Satellite observations document a substantial decline in the excess Hunga water vapor beginning in 2024 and continuing into 2025 — the largest drop recorded since the eruption.
The excess is decaying with an e-folding time of roughly three years. Projections based on current trends indicate stratospheric water vapor will return toward pre-eruption background levels around 2030.
As the excess water vapor diminishes, so too does its warming influence. Global temperatures have responded accordingly:
- 2025 was cooler than both 2023 and the 2024 peak across multiple datasets.
- Berkeley Earth reported 2025 as the third-warmest year on record but noted clear cooling relative to the prior two years.
- January 2026 ran 0.28°C cooler than the record-warm January of 2025 (Copernicus ERA5).
- Satellite lower-troposphere records show the post-2023/2024 peak decline continuing into early 2026.
This is exactly the behavior expected from a temporary atmospheric pulse of water vapor rather than a permanent acceleration driven by steadily rising CO₂. The “accelerating crisis” narrative predicted relentless upward pressure; instead, we see a natural spike that is now fading on schedule.
Natural Drivers Dominate Short-Term Climate Signals
Hunga Tonga provides a real-world experiment in atmospheric physics. A single natural event injected the dominant greenhouse gas into the stratosphere at record levels. Global temperatures responded with a clear spike. As that injection dissipates, temperatures are moderating.
This does not deny longer-term trends or the role of CO₂. It demonstrates that natural forcings — volcanic water vapor in this case — can produce significant, observable short-term excursions that must be properly accounted for before attributing every wiggle exclusively to human emissions.
The data from NASA’s own instruments, MLS water vapor records, and multiple independent temperature series back the core claim: the recent temperature spike had a major natural component from Hunga Tonga, and that component is now waning as the excess stratospheric water vapor declines.
Earth’s climate continues to show the fingerprints of natural variability alongside any anthropogenic influence. The Hunga Tonga pulse is fading — precisely as the physics of a temporary water vapor injection predicted.