Hunga Tonga-Hunga Ha’apai (Hunga Tonga for short) erupted on January 15, 2022 in the Pacific Kingdom of Tonga. It created a tsunami that triggered warnings throughout the Pacific basin and sent sound waves around the globe repeatedly.
A new study published in the Journal of Climate investigates the climate impacts of this eruption.
Our findings suggest that the volcano could explain last year’s exceptionally large ozone hole, as well as the much wetter-than-expected summer of 2024.
The eruption could have lasting effects on our winter weather for years to come.
A cooling cloud of smoke
Normally, the smoke from a volcano – and in particular the sulfur dioxide contained in the smoke cloud – ends up cooling the Earth’s surface for a short period of time.
That’s because sulfur dioxide is transformed into sulfate aerosols, which send sunlight back into space before it reaches the surface. This shading effect means that the surface is cooled for a while until the sulfate falls back to the surface or it starts to rain.
This did not happen with Hunga Tonga.
Being an underwater volcano, Hunga Tonga produced little smoke but a lot of water vapor: 100–150 million tons, or the equivalent of 60,000 Olympic swimming pools. The immense heat of the eruption turned vast amounts of seawater into steam, which was then shot high into the atmosphere by the force of the eruption.
All that water ended up in the stratosphere: a layer of the atmosphere between about 15 and 40 kilometers above the surface that produces neither clouds nor rain because it is too dry.
Water vapor in the stratosphere has two main effects. First, it helps in the chemical reactions that destroy the ozone layer, and second, it is a very powerful greenhouse gas.
There is no precedent in our observations of volcanic eruptions to know what all this water will do to our climate and for how long. This is because the only way to measure water vapor throughout the stratosphere is through satellites. They have only been around since 1979 and in that time there has not been an eruption like Hunga Tonga.
Follow the steam
Experts in stratospheric science around the world began examining the 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 post-eruption evolution, some concentrated on the possible effects of water vapor, and some included both.
But no one knew how water vapor would behave in the stratosphere. How long will it stay in the stratosphere? Where will he go? And most importantly, what does this mean for the climate while the water vapor is still there?
These are exactly the questions we set out to answer.
We wanted to know about the future and unfortunately it is impossible to measure it. That’s why we turned to climate models that are specifically designed to look into the future.
We ran two simulations with the same climate model. In one we assumed no volcano had erupted, 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 must be due to the added water vapor.
What did we find out?
The Great Ozone Hole from August to December 2023 is at least partly due to Hunga Tonga. Our simulations predicted the ozone hole almost two years in advance.
It should be noted that this was the only year in which we would expect a volcanic eruption to have an impact on the ozone hole. By then, the water vapor has had enough time to reach the polar stratosphere over Antarctica, and in the coming years there will not be enough water vapor left to expand the ozone hole.
As the ozone hole lasted until the end of December, with it came a positive phase of the southern annular mode in the summer of 2024. For Australia, this meant a greater chance of a wet summer, which was the exact opposite of what most people expected with the announced El Nino. Again, our model predicts this two years ahead.
In terms of global average temperatures, which are a measure of how much climate change we are experiencing, the impact of Hunga Tonga 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 cannot be attributed to the Hunga Tonga eruption.
A hiatus for the rest of the decade
But there are some surprising, lasting impacts in some regions of the planet.
For the northern half of Australia, our model predicts colder and wetter than normal winters until about 2029. For North America, it predicts warmer than normal winters, while for Scandinavia it again predicts colder than normal winters.
The volcano appears to change the way some waves travel through the atmosphere. And atmospheric waves are responsible for the highs and lows that directly affect our weather.
It is important to clarify here that this is only one study and one particular way of investigating what impact the Hunga Tonga eruption may have on our weather and climate. Like any climate model, ours is not perfect.
We also did not include any other effects such as the El Niño–La Niña cycle. But we hope that our research will spark scientific interest in trying to understand what such a large amount of water vapor in the stratosphere might mean for our climate.
Whether it will confirm or refute our findings remains to be seen – we welcome both results.
Martin JuckerLecturer in Atmospheric Dynamics, UNSW Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.
