In January 2022, the Hunga Tonga-Hunga Ha'apai volcano erupted, releasing immense quantities of methane into the atmosphere. Yet satellite instruments observed a simultaneous destruction of this greenhouse gas. How is this possible? The answer lies in the volcanic plume, where record concentrations of formaldehyde were detected. This compound results from the breakdown of methane.
This phenomenon relies on a mechanism involving iron salt aerosols. During the eruption, volcanic ash and salty seawater were propelled into the stratosphere. Under the sun's influence, these particles release chlorine, a highly reactive element that breaks down methane. This process had already been observed above the Sahara, but never in the stratosphere. Matthew Johnson, from the University of Copenhagen, notes that this similarity is completely unexpected.
The eruption of the Hunga Tonga-Hunga Ha'apai volcano on January 15, 2022.
Credit: Tonga Geological Services Using the Sentinel-5P satellites equipped with the TROPOMI instrument, scientists tracked the formaldehyde cloud for ten days. Maarten van Herpen, lead author of the study, explains that formaldehyde only persists for a few hours, proving that methane destruction continued over a long period. The researchers had to correct the data to account for the unusual altitude and interference from sulfur dioxide, thereby confirming the reality of the phenomenon.
The eruption released about 300 gigagrams of methane, equivalent to the annual emissions of more than two million cows. At the same time, the volcanic plume was eliminating nearly 900 megagrams of methane per day. This dual effect shows that volcanoes can both pollute and cleanse the atmosphere, although the overall balance is not in favor of cleansing.
Methane is a powerful greenhouse gas, 80 times more effective than CO₂ at trapping heat over a 20-year period. However, it persists for a shorter time in the atmosphere, about a decade. Reducing methane emissions could therefore slow warming in the short term, acting as a climate emergency brake. Nevertheless, reducing CO₂ remains essential for long-term balance.
Satellite image from January 16, 2022 showing the formaldehyde cloud (in blue) measured by TROPOMI.
Credit: van Herpen et al. (2026)
This discovery could inspire technologies aimed at removing methane from the atmosphere. Current methods struggle to prove their effectiveness, but the study shows that satellites can directly measure its destruction. Jos de Laat, from the Royal Netherlands Meteorological Institute, explains that this approach makes it possible to verify whether the techniques work. The researchers hope to develop safe and effective solutions to combat warming.
Furthermore, these results require a revision of the overall methane budget. Until now, models ignored the effect of atmospheric dust, such as volcanic ash, on methane degradation. Matthew Johnson insists on the need to correct these estimates to better understand the methane cycle and its impact on climate.