When Hunga Tonga-Hunga Ha’apai erupted beneath the South Pacific in January 2022, the explosion ranked among the most powerful volcanic events of the modern era. But researchers have now uncovered an unexpected consequence of that eruption: the enormous volcanic cloud appears to have helped destroy some of the methane pollution produced by the volcano itself.
The finding could have implications far beyond a single eruption. Scientists are increasingly interested in ways to reduce methane in the atmosphere because the gas is a major contributor to global warming and disappears much faster than carbon dioxide. Understanding how nature can accelerate that process could eventually help researchers develop new strategies for slowing near-term warming.
A Strange Signal in the Volcano Cloud
Researchers made the discovery using satellite observations of the huge plume created by the eruption. They detected exceptionally high levels of formaldehyde, a chemical that provided an important clue about what was happening inside the cloud.
Formaldehyde is produced briefly during the chemical reactions that break methane apart in the atmosphere. Because it survives for only a short time, unusually large amounts of formaldehyde can act as a chemical fingerprint showing that methane destruction is actively taking place.
“When we analyzed the satellite images, we were surprised to see a cloud with a record-high concentration of formaldehyde. We were able to track the cloud for 10 days, all the way to South America. Because formaldehyde only exists for a few hours, this showed that the cloud must have been destroying methane continuously for more than a week,” explains Dr. Maarten van Herpen from Acacia Impact Innovation BV, first author of the study, which was published in Nature Communications.
“It is known that volcanoes emit methane during eruptions, but until now it was not known that volcanic ash is also capable of partially cleaning up this pollution,” he adds.
Daily Emissions From 2 Million Cows
According to the researchers’ calculations, the volcano released around 300 gigagrams (Gg) of methane during the eruption. That is roughly equivalent to the annual methane emissions of more than two million cows.
At the same time, the plume removed approximately 900 megagrams (Mg) of methane per day, an amount comparable to the daily emissions of two million cows.
Salt, Sunlight and Unexpected Chemistry
The researchers believe the explanation involves an unusual combination of volcanic ash, seawater and sunlight. The basic chemistry was first identified by scientists in 2023, although in a very different environment.
In that earlier research, scientists found that Saharan dust carried across the Atlantic Ocean can mix with sea salt released by breaking waves. Together, these materials form tiny airborne particles called iron salt aerosols. Aerosols are microscopic particles suspended in the atmosphere.
When sunlight strikes those particles, chemical reactions can release chlorine atoms. Chlorine is highly reactive, allowing it to attack methane molecules and help break them apart. The discovery added a previously underappreciated process to scientists’ understanding of chemistry in the troposphere, the lowest major layer of Earth’s atmosphere where most weather occurs.
“What is new — and completely surprising — is that the same mechanism appears to occur in a volcanic plume high up in the stratosphere, where the physical conditions are entirely different,” says Professor Matthew Johnson from the Department of Chemistry at the University of Copenhagen, one of the researchers behind both discoveries.
The Hunga Tonga eruption created unusually favorable conditions for this chemistry. Because the volcano erupted beneath the ocean, it blasted enormous quantities of salty seawater upward along with volcanic ash. Some of that material reached the stratosphere, the atmospheric layer above the troposphere.
Researchers propose that sunlight striking this mixture produced highly reactive chlorine. Those chlorine atoms then reacted with methane in the plume, helping destroy some of the methane released during the eruption. The extraordinary amounts of formaldehyde detected from space provided evidence that this process was taking place.
Why Destroying Methane Matters
Methane currently accounts for about one third of global warming. Although it is far less abundant than carbon dioxide, methane traps heat extremely efficiently. Over a 20-year period, methane is about 80 times as potent as CO2.
There is also an important difference between the two greenhouse gases. Methane typically remains in the atmosphere for about 10 years before chemical reactions remove it, while a portion of carbon dioxide can influence the climate for far longer.
That relatively short atmospheric lifetime makes methane an especially attractive target for rapid climate action. Cutting methane emissions today could begin producing a noticeable climate benefit within about a decade.
For that reason, researchers sometimes describe methane reduction as an “emergency brake” on climate change, because rapidly lowering methane levels could help reduce warming during the coming decades and potentially lower the risk of crossing dangerous climate tipping points.
Reducing methane, however, is not a substitute for reducing carbon dioxide. Long-term temperature stabilization still requires major reductions in CO2 emissions.
Could Scientists Copy What the Volcano Did?
The discovery could also provide inspiration for researchers and companies investigating ways to accelerate methane destruction deliberately.
One emerging area of climate research focuses on atmospheric methane removal. Instead of only preventing new methane emissions, scientists are exploring whether chemical processes could safely increase the rate at which methane already in the atmosphere is broken down.
Hunga Tonga may have provided a dramatic natural demonstration of one possible mechanism.
A major challenge, however, is proving that any proposed technology actually removes methane. Atmospheric methane is spread across enormous areas, making relatively small changes difficult to measure with confidence.
“How do you prove that methane has been removed from the atmosphere? How do you know your method works? It’s very difficult. But here we address that problem by showing that methane breakdown can in fact be observed using satellites,” says Dr. Jos de Laat from the Royal Netherlands Meteorological Institute, senior author of the study.
Changing the Methane Budget
The findings may also force scientists to reconsider calculations of the global methane budget.
The methane budget is essentially an accounting system for the gas. Scientists estimate how much methane enters the atmosphere from sources such as wetlands, agriculture, fossil fuels and geological activity, then compare that with the amount removed through atmospheric chemistry and other processes.
According to the researchers, atmospheric dust has not previously been fully incorporated into those calculations. If volcanic ash and other forms of mineral dust can accelerate methane destruction, estimates of how methane moves through the atmosphere may need to be adjusted.
“We now know that atmospheric dust — for example from a volcanic eruption — impacts the methane budget, meaning the budget of how much methane is added to the atmosphere and how much is removed. Because dust has not previously been taken into account, it is important that we correct the data on which these estimates are based,” says Matthew Johnson.
Satellites Watched the Chemistry Unfold
The researchers used measurements from TROPOMI, an advanced instrument aboard the European Space Agency’s Sentinel-5P satellite. TROPOMI scans Earth’s atmosphere every day, monitoring gases associated with air pollution and climate change.
Detecting formaldehyde inside a volcanic plume in the stratosphere, however, pushed the instrument well beyond the conditions for which its standard measurements are normally designed.
“Retrieving formaldehyde from TROPOMI in a stratospheric volcanic plume is far outside the instrument’s standard operating conditions — we had to carefully correct the satellite’s sensitivity for the unusual altitude of the signal and account for interference from the high sulfur dioxide concentrations. Getting these corrections right was essential to confirm that what we were seeing was real,” said Dr. Isabelle De Smedt, Royal Belgian Institute for Space Aeronomy.
Those corrections allowed the researchers to conclude that the unusually strong formaldehyde signal was genuine and could be used to track methane destruction within the volcanic cloud.
A Possible Blueprint From Nature
The team believes the discovery could encourage engineers to investigate whether the natural chemistry observed after Hunga Tonga can be reproduced safely and effectively.
“It’s an obvious idea for industry to try to replicate this natural phenomenon — but only if it can be proven to be safe and effective. Our satellite method could offer a way to help figure out how humans might slow global warming,” concludes Matthew Johnson.
Any attempt to manipulate atmospheric chemistry would require careful study to understand potential unintended effects. But Hunga Tonga provides researchers with an unusual real-world example of methane destruction occurring on a huge scale, along with a possible way to monitor the process from space.
About the Study
The scientific article was published in Nature Communications.
The researchers behind the study are Maarten van Herpen (Acacia Impact Innovation BV, Netherlands); Isabelle De Smedt (Royal Belgian Institute for Space Aeronomy, Belgium); Daphne Meidan and Alfonso Saiz-Lopez (CSIC, Spain); Matthew Johnson (University of Copenhagen, Denmark); Thomas Röckmann (Utrecht University, Netherlands); and Jos de Laat (Royal Netherlands Meteorological Institute, Netherlands).
The research was supported by Spark Climate Solutions.
