The massive 2022 eruption of the Hunga Tonga Hunga Ha’apai volcano appears to have triggered a previously unrecognized chemical process that destroyed methane in the atmosphere according to a study published in Nature Communications.
Researchers detected unusually high concentrations of formaldehyde in the volcanic plume using satellite observations. Because formaldehyde is produced during the atmospheric breakdown of methane and remains present for only a few hours, its sustained presence provided evidence that methane oxidation continued inside the plume for more than a week.
The Hunga Tonga Hunga Ha’apai volcano erupted beneath the South Pacific on January 15, 2022 sending a huge mixture of volcanic material and seawater into the atmosphere. Researchers estimate that the eruption released about 300 gigagrams of methane.
At the same time the volcanic plume removed an estimated 900 megagrams of methane per day, according to the study. The researchers said this amount is comparable to the daily methane emissions of around two million cows.
The process appears to have involved an unusual combination of volcanic ash, seawater and sunlight. Earlier research had shown that mineral dust and sea salt can form iron salt aerosols, which release highly reactive chlorine atoms when exposed to sunlight.
Chlorine can react with methane molecules and accelerate their breakdown. The researchers propose that a similar process occurred in the Hunga Tonga plume, where seawater and volcanic ash were injected into the stratosphere.
“What is new and completely surprising is that the same mechanism appears to occur in a volcanic plume high up in the stratosphere,” said University of Copenhagen chemistry professor Matthew Johnson, one of the researchers.
The discovery is significant because methane is a major contributor to global warming. Although it is present in much smaller quantities than carbon dioxide methane has a much stronger warming effect over shorter time periods and remains in the atmosphere for roughly a decade.
Its relatively short atmospheric lifetime means that reducing methane concentrations can potentially produce climate benefits much faster than reducing carbon dioxide alone. The researchers therefore say understanding natural processes that remove methane could improve estimates of the global methane budget and inform future research into atmospheric methane removal.
The study also highlights the potential role of atmospheric dust and volcanic material in methane chemistry. The researchers said such processes have not been fully incorporated into existing calculations of how much methane enters and leaves the atmosphere.
The team used observations from the European Space Agency Sentinel-5P satellite and its TROPOMI instrument to track the formaldehyde signal in the volcanic plume. Detecting the gas at such high altitudes required adjustments to account for the unusual conditions and interference from high concentrations of sulphur dioxide.
The researchers said the satellite observations could also provide a way to monitor methane destruction in the atmosphere. This could be important if scientists eventually develop technologies intended to accelerate methane removal.
However, the study does not demonstrate that the volcanic process can be safely or economically replicated as a climate intervention. Any deliberate attempt to alter atmospheric chemistry would require extensive research into potential environmental effects.
The findings instead provide a natural example of methane destruction on a large scale and suggest that volcanic and mineral aerosols may play a previously underestimated role in regulating atmospheric methane levels.