Hunga Tonga-Hunga Ha’apai (Hunga Tonga for short) erupted on January 15, 2022 in the Pacific kingdom of Tonga. It caused a tsunami that triggered warnings throughout the Pacific basin and sent sound waves around the world several times.
A new study published in the Journal of climate examines the climate effects of this eruption.
Our findings show that the volcano can explain last year’s extraordinarily large ozone hole, as well as the much wetter-than-expected summer of 2024.
The eruption could have lingering effects on our winter weather for years to come.
A cooling cloud of smoke
Typically, the smoke from a volcano – and in particular the sulfur dioxide contained in the smoke cloud – eventually cools the Earth’s surface for a short period of time.
This is because the sulfur dioxide is converted into sulfate aerosols, which send sunlight back into space before it reaches the surface. This shadow effect cools the surface for a while until the sulphate falls back onto the surface or rains out.
This is not what happened before Hunga Tonga.
Because it was an underwater volcano, Hunga Tonga produced little smoke, but a lot of water vapor: 100 to 150 million tons, or the equivalent of 60,000 Olympic swimming pools. The enormous heat of the eruption transformed enormous amounts of seawater into steam, which then shot high into the atmosphere with the force of the eruption.
All that water ended up in the stratosphere: a layer of the atmosphere between about 15 to 40 kilometers above the surface, where clouds or rain do not form because it is too dry.
Water vapor in the stratosphere has two important effects. First, it aids in the chemical reactions that destroy the ozone layer, and second, it is a very potent greenhouse gas.
There is no precedent in our observations of volcanic eruptions to know what all that water would do to our climate, and for how long. This is because the only way to measure water vapor in the entire stratosphere is via satellites. These have only existed since 1979 and there has been no eruption comparable to that of Hunga Tonga in that time.
Follow the vapor
Experts in stratospheric science around the world began examining satellite observations from the first day of the eruption. Some studies focused on the more traditional effects of volcanic eruptions, such as the amount of sulfate aerosols and their evolution after the eruption, some focused on the possible effects of the water vapor, and some included both.
But no one really knew how the water vapor in the stratosphere would behave. How long will it stay in the stratosphere? Where will it go? And above all: what does this mean for the climate as long as the water vapor is still there?
Those were exactly the questions we were going to answer.
We wanted to find out more about the future, but unfortunately it is impossible to measure that. That’s why we turned to climate models, which are specially made to look into the future.
We did two simulations with the same climate model. In one case we assumed no volcano would erupt, while in the other we manually added 60,000 Olympic swimming pools’ worth of water vapor to the stratosphere. We then compared the two simulations, knowing that any differences had to be due to the added water vapor.
What have we discovered?
The large ozone hole from August to December 2023 was at least partly due to Hunga Tonga. Our simulations predicted that ozone hole almost two years in advance.
Notably, this was the only year in which we would expect to see any impact from the volcanic eruption on the ozone hole. By then, the water vapor had just enough time to reach the polar stratosphere above Antarctica, and in subsequent years there will not be enough water vapor left to expand the ozone hole.
Because the ozone hole lasted until the end of December, a positive phase of the Southern Annular Mode occurred in the summer of 2024. For Australia, this meant a higher chance of a wet summer, which was the exact opposite of what most people expected with the declared El Nino. Again, our model predicted this two years ahead.
In terms of global average temperatures, which are a measure of the magnitude of climate change we are experiencing, Hunga Tonga’s impact is very small, only about 0.015 degrees Celsius. (This was independently confirmed by another study.) This means that the incredibly high temperatures we have been measuring for about a year now cannot be attributed to the Hunga Tonga eruption.
Disruption for the rest of the decade
But there are some surprising, lasting consequences in some parts of the planet.
For the northern half of Australia, our model predicts colder and wetter winters than usual until about 2029. For North America it predicts warmer than usual winters, while for Scandinavia it predicts colder than usual winters again.
The volcano appears to change the way some waves travel through the atmosphere. And atmospheric waves are responsible for highs and lows, which directly affect our weather.
It is important to clarify here that this is just one study, and one specific way to investigate what impact the Hunga Tonga eruption could have on our weather and climate. Like any other climate model, ours is not perfect.
We also did not include other effects such as the El Niño-La Niña cycle. But we hope our study will spark scientific interest in trying to understand what such a large amount of water vapor in the stratosphere could mean for our climate.
Whether this confirms or contradicts our findings remains to be seen – we welcome both outcomes.
Martin JuckerLecturer in Atmospheric Dynamics, UNSW Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.