A new study shows that the eruption of the Tonga volcano could cause unusual weather for the rest of the decade

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 several times around the world.

A new study published in Journal of Climate examines the climatic effects of this eruption.

Our findings show that the volcano may explain last year’s exceptionally large ozone hole, as well as the much wetter summer of 2024 than expected.

The eruption could have lingering effects on our winter weather for years to come.

A cooling cloud of smoke

Volcanic smoke—and especially the sulfur dioxide contained in the smoke plume—usually ends up cooling the Earth’s surface for a short period of time.

This is because sulfur dioxide is converted into sulfate aerosols, which send sunlight back into space before it reaches the surface. This shielding effect means that the surface cools for a while until the sulfate falls back to the surface or rains.

That didn’t happen for Hung Tong.

Being an underwater volcano, Hunga Tonga produced little smoke but a lot of steam: 100-150 million tonnes, 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 this water ended up in the stratosphere: a layer of the atmosphere about 15 to 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 chemical reactions that destroy the ozone layer, and second, it is a very strong 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. The only way to measure water vapor in the entire stratosphere is with satellites. These have only been around since 1979 and there hasn’t been a Hung Tonga-like eruption in that time.

Follow the couple

Stratospheric science experts 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 water vapor, and some included both.

But nobody really knew how water vapor in the stratosphere would behave. How long will it stay in the stratosphere? where will it go? And most importantly, what does it mean for the climate if water vapor is still there?

These were exactly the questions we set out to answer.

We wanted to inform ourselves about the future, and unfortunately that cannot be measured. That’s why we turned to climate models that are specifically built to look into the future.

We performed two simulations with the same climate model. In one, we assumed that no volcano had erupted, while in the other, we manually added 60,000 Olympic-size pools 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 was at least partially caused by Hung Tonga. Our simulations predicted the ozone hole almost two years in advance.

Notably, this was the only year we would expect any effect of a volcanic eruption on the ozone hole. By then, water vapor has had just enough time to reach the polar stratosphere over Antarctica, and in later years there won’t be enough water vapor left to increase the ozone hole.

As the ozone hole lasted until the end of December, with it came a positive phase of the southern annular mode during the summer of 2024. This meant a higher chance of a wet summer for Australia, which was exactly the opposite of what most people expected with the declared El. Nino. Again, our model predicted this two years ahead.

In terms of average global temperatures, which are a measure of how much climate change we are experiencing, Hung Tong’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’ve been measuring for about a year now cannot be attributed to the Hung Tong eruption.

Disruption for the rest of the decade

However, there are surprising, lasting impacts in some areas of the planet.

For the northern half of Australia, our model predicts colder and wetter-than-normal winters until 2029. For North America, it predicts warmer-than-normal winters, while Scandinavia 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 ups and downs that directly affect our weather.

It is important to clarify here that this is only one study and one specific way to investigate what impact the Hung Tong eruption could have on our weather and climate. Like any other climate model, ours is not perfect.

We also did not include any other effects such as the El Niño–La Niña cycle. However, we hope that our study will stimulate scientific interest to try to understand what such an amount of water vapor in the stratosphere could mean for our climate.

Whether this is to confirm or refute our findings remains to be seen – we welcome both results.