Javier Vinós on the Hunga Tonga Eruption and its extraordinary Climate Effects

The Hunga Tonga eruption was unprecedented in modern observation. Located about 150 meters below sea level in the South Pacific, it injected an estimated 150 million tons of water vapor into the stratosphere, increasing stratospheric water vapor concentrations by roughly 10%. Unlike typical major volcanic eruptions, which primarily emit sulfur aerosols that cool the Earth’s surface, this eruption’s dominant effect was the injection of water vapor—a greenhouse gas—into the stratosphere. Vinós notes that previous research has shown that a 10% reduction in stratospheric water vapor can reduce the rate of global surface warming by 25%. By analogy, a 10% increase could produce significant warming.

Volcanic effects on climate are typically categorized as chemical (ozone-destroying reactions involving sulfur and chlorine), radiative (cooling from sulfate aerosols reflecting sunlight), and dynamic (changes in atmospheric circulation). While chemical and radiative effects are relatively well understood and included in climate models, dynamic effects—particularly changes to stratospheric circulation and their transmission to the troposphere—are less understood and poorly represented in models. Vinós argues that these dynamic mechanisms are central to explaining the recent climate anomalies.

Beginning in late 2022 and intensifying through 2023 and 2024, a series of extreme and statistically rare climate anomalies occurred worldwide. Berkeley Earth characterized the period as an exceptional warming spike from 2023 to 2025. Climate models reportedly estimate the probability of such an event at only 0.2%, suggesting that internal variability and incremental CO₂ increases alone are insufficient explanations.

Anomalies

The anomalies were global and diverse. Antarctic sea ice reached record low extents in 2022 and broke further records in 2023. The Amazon River basin experienced its lowest water levels in 120 years. California recorded a historically wet and unusually cold season, with record atmospheric rivers and its snowiest winter in over seven decades. In contrast, New York City experienced its least snowy season on record. Cyclone Freddy in the Indian Ocean set a duration record, and in 2024 the Intertropical Convergence Zone shifted more than two degrees north of its normal position, bringing unusual rainfall to the Sahara. The first half of the 2024 hurricane season was unexpectedly quiet, defying forecasts.

Globally, 42% of the Earth’s surface recorded temperatures above two standard deviations from the expected value in 2023, and 2024 followed with additional records—an unusual pattern given that record-warm years are typically followed by cooler ones. The winter of 2023–2024 saw three Southern Hemisphere stratospheric warming events, a frequency that models suggest occurs only once every 250 years. Low cloud cover anomalies were also the most negative ever recorded.

Vinós rejects several alternative explanations for the climate event. He argues that the 2023 El Niño was only moderate in strength and began after the initial anomalies appeared in late 2022. The warming pattern did not follow the typical El Niño sequence, in which tropical warming follows changes in the Niño region. He also dismisses the idea that three consecutive La Niña events from 2020 to 2022 were responsible, noting that similar sequences have occurred before without producing such global effects. Likewise, he considers the reduction in sulfur emissions from shipping regulations since 2020 too small and too gradual to account for the magnitude and temporary nature of the event.

Occam’s Razor

Instead, Vinós applies Occam’s Razor and identifies the Hunga Tonga eruption as the most plausible single cause. He emphasizes that stratospheric circulation changes unfold slowly; water vapor injected in early 2022 would take about a year to reach the Northern Hemisphere and influence the polar vortex, aligning with the timing of the 2023 anomalies.

He compares Hunga Tonga to the 1815 eruption of Mount Tambora. In Tambora’s case, the most severe climatic impacts, including the ‘Year Without a Summer’ in 1816, occurred more than a year after the eruption. Vinós argues that climate models have difficulty accurately simulating Tambora’s effects, particularly dynamic atmospheric responses, and therefore may also be unreliable in assessing Hunga Tonga’s impact.

By 2024, significant global cooling had begun. According to satellite temperature records, the cooling period starting in March 2024 ranks among the largest in 46 years. Unlike previous cooling episodes, which were associated with La Niña events or the 1991 Pinatubo eruption, this cooling lacks a clearly defined conventional cause. Vinós suggests that this, too, is part of this volcanic-driven climate event.

Finally, he critiques the official scientific and political response. He argues that institutions have attributed the 2023 warming primarily to human greenhouse gas emissions and have downplayed or dismissed the potential role of Hunga Tonga, focusing only on radiative effects while ignoring dynamic mechanisms. A consensus report, he claims, concluded prematurely that the eruption could not explain the event, discouraging alternative interpretations.

Vinós concludes that the convergence of numerous rare global anomalies, their timing, and historical parallels strongly support the Hunga Tonga eruption as the principal cause of the 2023–2024 climate event. He contends that the inability of current models and consensus frameworks to explain these developments reveals significant gaps in climate science understanding.

Watch the lecture by Dr. Vinós below: