The eruption of the Hunga Tonga-Hunga Ha’apai (Hunga Tonga) volcano on January 15, 2022, has had far-reaching climatic consequences, according to a recent study published in the Journal of Climate.
The underwater volcanic eruption in the Pacific Kingdom of Tonga created a tsunami that prompted warnings across the Pacific basin and sent sound waves around the globe multiple times.
The study suggests that the Hunga Tonga eruption can explain the unusually large ozone hole observed last year and the unexpectedly wet summer of 2024.
Furthermore, it could have lingering effects on winter weather for years to come.
Unusual volcanic effects
Typically, volcanic eruptions release sulphur dioxide, which forms sulphate aerosols in the atmosphere.
These aerosols reflect sunlight back into space, causing a temporary cooling of the Earth's surface.
However, the Hunga Tonga eruption was different. Being an underwater volcano, it produced minimal smoke but released a significant amount of water vapour—between 100 to 150 million tonnes, equivalent to 60,000 Olympic swimming pools.
The intense heat of the eruption turned vast quantities of seawater into steam, which was propelled high into the atmosphere.
This water vapour reached the stratosphere, a layer between 15 and 40 kilometers above the Earth's surface that is typically too dry for cloud formation or rain.
Water vapour in the stratosphere has two main effects: it facilitates chemical reactions that destroy the ozone layer and acts as a potent greenhouse gas.
The unprecedented amount of water vapour from the eruption presents a unique scenario for climate scientists, as there has been no similar volcanic event in the satellite observation era, which began in 1979.
Tracking the vapour
Scientists specialising in stratospheric studies began analyzing satellite data from the eruption's outset.
Various studies examined traditional volcanic effects, such as sulphate aerosol evolution, as well as the impacts of water vapour.
However, the behavior of the water vapour in the stratosphere and its climatic implications remained uncertain.
To address this, researchers turned to climate models. They conducted two simulations: one without the eruption and one with the added water vapour.
By comparing these simulations, they isolated the effects of the water vapour.
The study found that the large ozone hole observed from August to December 2023 was partly due to the Hunga Tonga eruption.
The model predicted this anomaly nearly two years in advance.
However, the impact on the ozone hole is expected to be a one-time occurrence, as the water vapour will dissipate over time.
Unexpected weather patterns
The extended ozone hole caused a positive phase of the Southern Annular Mode during the summer of 2024, leading to a wetter-than-expected summer in Australia despite the presence of El Niño conditions.
The model had accurately predicted this weather pattern two years earlier.
In terms of global mean temperatures, the Hunga Tonga eruption's impact is minimal, estimated at only about 0.015 degrees Celsius.
This finding aligns with another independent study, indicating that the recent high global temperatures are not attributable to the eruption.
Long-term regional effects
The study also predicts surprising, lasting impacts on regional climates. For northern Australia, colder and wetter winters are expected until around 2029.
In contrast, North America might experience warmer winters, while Scandinavia could face colder winters. These changes are attributed to the alteration in atmospheric wave patterns caused by the eruption.
The study highlights the complexity of predicting climate impacts from such an unprecedented event.
It is a call to the scientific community to further investigate the implications of large amounts of water vapour in the stratosphere.
The researchers acknowledge the limitations of their model, including the exclusion of factors like the El Niño–La Niña cycle.
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