Volcano plume may have silently broken methane

methane destruction – Satellite observations of the 2022 Hunga Tonga–Hunga Ha’apai eruption suggest chlorine-driven chemistry inside the ash-and-gas plume helped destroy methane for several days. Researchers say the event offers a rare way to test whether methane-removal ideas coul

On the morning the Hunga Tonga–Hunga Ha’apai volcano erupted. a plume rose 55 kilometers into the sky—ash. gas and seawater propelled upward by an explosion researchers describe as powerful as several atomic bombs. But the scientific shock came later. when satellites started tracking a chemical fingerprint that suggested something unexpected had happened inside that airborne mix.

In January 2022. the South Pacific eruption was followed by researchers now reporting that chemical reactions inside the plume may have partially cleaned up some of the volcano’s own pollution by breaking down methane. a potent greenhouse gas. Their results, published May 7 in Nature Communications, rely on satellite data that tracked methane destruction. The work points to a practical question for climate efforts: if scientists can measure methane breakdown during a natural event. they may be able to evaluate proposals to accelerate methane removal from the atmosphere.

Methane matters for climate largely because of how it behaves in the air. It’s responsible for roughly one-third of present-day global warming. Even though methane traps more heat than carbon dioxide. it has one key advantage for would-be removal strategies: it persists in the atmosphere for only about a decade. compared with the centuries CO2 can linger. That relatively short lifetime has made methane an attractive target for geoengineering schemes aimed at speeding up its breakdown.

The catch is measurement. A reliable way to judge whether a methane removal tactic is working is a prerequisite for trying it at all. said Maarten van Herpen. a physicist with Acacia Impact Innovation. a consulting firm in Heesch. Netherlands. The eruption offered him and colleagues a rare opportunity to test whether methane destruction could be quantified from space. “If we can see it in the volcano, we would also see it in a hypothetical intervention,” van Herpen said.

The chemistry they investigated is built around chlorine atoms—highly reactive fragments that can help strip methane molecules apart. Earlier work by van Herpen and colleagues suggested that chlorine atoms can form when iron-rich dust blown from the Sahara Desert mixes with salt-rich sea spray over the Atlantic Ocean. Sunlight drives reactions between the iron and the salt, freeing chlorine in a highly reactive atomic form.

This time, the researchers suspected that volcanic ash might set off similar reactions. The 2022 eruption, they say, created unusually favorable conditions for the test.

To look for evidence of this kind of chlorine-driven methane loss. the team turned to the European Space Agency’s Tropospheric Monitoring Instrument. a satellite-based tool that monitors air pollution and greenhouse gases globally. Measuring methane directly over the ocean is difficult, the researchers note, because water absorbs light at similar wavelengths. Instead, they watched for formaldehyde as a proxy for reactive chlorine.

Formaldehyde isn’t emitted by volcanoes. It forms as methane degrades. And the satellite data showed that formaldehyde remained detectable in the volcanic plume for several days—even though it normally breaks down within hours. That timing mismatch, researchers say, suggests formaldehyde was being continuously produced by ongoing chemical reactions.

“It is quite surprising that these formaldehyde levels were observed,” said Folkert Boersma, an atmospheric scientist at Wageningen University & Research in the Netherlands who was not involved in the study. “That points to something that I did not know myself.”

The eruption’s setting helped make the chemistry plausible on a massive scale. Chlorine is not usually a major component of volcanic eruptions, but this explosion occurred 150 meters below sea level. The researchers estimate it lofted more than a hundred million metric tons of salty water into the atmosphere. With that seawater added to the mix of ash and emissions. van Herpen’s team estimates that chlorine-driven reactions destroyed roughly 900 tons of methane per day after the eruption. The figure is modest compared with the eruption’s estimated total methane emission of 300. 000 tons—but it still indicates methane breakdown occurring inside the plume itself.

Not everyone is convinced that the lesson should be applied directly to geoengineering. Pete Edwards. an atmospheric chemist at the University of York in England. argued against “injection” approaches that would put chlorine into the upper atmosphere. “I don’t think we should go anywhere near injecting chlorine into the stratosphere. We’ve done that before. and it didn’t go well. ” Edwards said. pointing to chlorofluorocarbons—chlorinated chemicals that leaked into the atmosphere from sources including refrigerants and aerosol sprays. Those compounds drove severe ozone depletion and contributed to the Antarctic ozone hole.

Edwards’ concern is chemical timing and chemistry location. In his view. chlorine is far more likely to react with the atmosphere’s more abundant molecules. such as ozone. than with methane. which is relatively scarce. “That’s especially true in the cold stratosphere. where chlorine reacts with ozone about 380 times faster than it does with methane. ” he said. “Chlorine in the stratosphere is a bad thing.”.

Boersma, too, urged caution about what should come first. Before moving forward with any such schemes, he said, the priority should be emitting less methane and CO2. “We all know what to do,” he said. “It’s not shooting chlorine into the stratosphere, it’s just making sure that we reduce emissions.”

For now, the central takeaway is narrower and more technical than the policy debate around geoengineering. The Hunga Tonga–Hunga Ha’apai eruption—captured in part by an astronaut on the International Space Station. who photographed the plume on Jan. 16, 2022 shortly after the eruption—has given researchers a natural stress test for how to spot methane destruction from orbit. And if satellites can detect that breakdown inside a volcanic plume. those same tools may help scientists quantify whether future methane-removal proposals can deliver measurable climate benefits.

Whether that promise leads to new interventions—or simply strengthens the case for cutting emissions—turns on a single question that the chemistry can’t answer: where, and how safely, should humans try to replicate it?

Hunga Tonga Hunga Ha'apai methane destruction chlorine atoms formaldehyde Tropospheric Monitoring Instrument geoengineering Nature Communications climate change