Volcano Plume Reveals a New Way to Track Methane Loss

On 15 January 2022, a submarine volcano in the South Pacific unleashed the most violent eruption of the 21st century. While the world watched walls of water and heard sonic booms halfway around the globe, something equally remarkable was unfolding 30 kilometres above the ocean — invisible to the naked eye. A satellite named TROPOMI caught an extraordinary chemical signal inside the ash cloud: a massive spike in formaldehyde, a gas that forms only when methane is being destroyed. What scientists found there is now rewriting how we could track — and even verify — the removal of one of Earth's most dangerous greenhouse gases.

The Discovery That Upended Our View of the Eruption

Methane is the atmosphere's second most powerful greenhouse gas, currently responsible for about 0.5°C of the warming we are already living with. Unlike CO₂, it breaks down naturally within roughly 10 years — converting into CO₂ and water through a process called methane oxidation. That breakdown is what keeps methane from doing even more damage, but scientists have never had a reliable way to watch it happen from space, particularly over oceans.

The Hunga Tonga-Hunga Ha'apai (HTHH) eruption changed that. The blast was so extreme it drove volcanic material to record-breaking heights of up to 55 kilometres — deep into the stratosphere. It also injected an astonishing 146 teragrams of water vapour, roughly 10% of the entire stratospheric water burden. That chemically-charged environment, scientists now realise, became an accidental laboratory for atmospheric methane oxidation on a scale never previously observed.

Why Satellites Couldn't See This Before

The standard approach to tracking methane from space relies on reflected shortwave infrared light — but that method fails completely over dark ocean surfaces. Low reflectance means no signal, which creates a vast blind spot: the ocean covers 71% of Earth's surface, and it's precisely where much of the natural methane oxidation occurs and where proposed climate-intervention approaches would likely operate.

This new research, published in Nature Communications by van Herpen and colleagues, sidesteps that limitation entirely. Instead of tracking methane directly, it tracks formaldehyde — a proxy that reveals where methane is being broken down. TROPOMI detects HCHO using ultraviolet wavelengths, which work equally well over land and ocean alike. Think of it less like watching the fire and more like following the smoke.

A key finding that clinched this approach: HCHO has a midday photolysis lifetime of just 2.5 hours. Any formaldehyde released by the eruption itself would have been 95% gone by the first TROPOMI overpass, and 99.95% gone by the second. The fact that the signal was still enormous on day two — and persisted for over ten days — meant only one thing: something inside the plume was actively manufacturing it, continuously. That something was methane being destroyed.

How Did a Volcano Become a Methane-Removal Lab?

The numbers are staggering. TROPOMI recorded a formaldehyde concentration of 12 ppb (±10%) inside the stratospheric plume — more than 100 times higher than any HCHO level previously measured in the stratosphere. Previous records linked to biomass burning had topped out at under 0.1 ppb at 20 km altitude. This signal was in a different league entirely.

By dividing the HCHO enhancement by its known 2.5-hour photolysis lifetime, the team calculated a total methane oxidation rate of 900 ± 220 Mg (megagrams, or tonnes) per day inside the volcanic cloud. Peak local oxidation reached 60 ppb of methane per day on January 16, tapering to around 8 ppb per day by January 20–21 as the plume dispersed. The HCHO signal correlated tightly with aerosol optical depth and sulfate aerosol markers — but not with bromine monoxide (BrO), which is the usual suspect for chlorine activation in volcanic plumes. Something else was driving the chemistry.

That something appears to be chlorine radicals, produced at an estimated rate of 2–5 gigagrams per day. Chlorine is a far more aggressive oxidiser of methane than the hydroxyl (OH) radical that normally dominates — and the amounts required here far exceed what known volcanic chemistry can explain. This is where the story gets genuinely surprising.

What This Means for Fighting Climate Change

Here is where science collides with something genuinely urgent. Atmospheric methane concentrations are rising at their fastest pace in over 40 years, with record annual increases recorded in 2020 and 2021. Even if every technological option to cut methane emissions were deployed simultaneously, experts estimate emissions could only be reduced by about 50%. The rest — from wetlands, permafrost, and other natural sources — will keep warming the planet regardless.

That is why a new field called atmospheric methane removal is gaining serious scientific attention. One leading approach involves releasing iron-based particles into the atmosphere to catalytically generate chlorine radicals that oxidise methane. Another uses ocean-based electrolysis to produce chlorine from seawater. Both are theoretically viable — but until now, we've had no way to confirm they're working. Satellites that track methane directly can't see over the ocean. Ground monitors lack the coverage. The HCHO method described here fills that gap precisely.

Researchers have modelled large-scale methane removal scenarios involving 25 Gg of chlorine per hour removing over 3 Gg of CH₄ per hour. The HTHH plume, by contrast, was removing just 75 Mg per hour — yet it was clearly and confidently detectable from orbit. That margin of sensitivity means TROPOMI-style observations could verify real-world methane removal interventions, providing the independent monitoring that climate governance urgently needs. The National Academies of Sciences had flagged the absence of exactly such a verification tool as a critical gap — this paper is a direct answer to that call.

The Questions That Still Need Answering

This is a proof-of-concept study, and the authors are refreshingly honest about where it still falls short. The HCHO method struggles wherever competing formaldehyde sources exist — biomass burning smoke from Australia muddied the signal for several clouds in the study, making full quantification impossible. The method also cannot directly measure methane; it infers methane oxidation from HCHO chemistry. And the iron-chloride mechanism, while plausible and well-supported by the numbers, remains unconfirmed — dedicated plume-resolving models and laboratory experiments are needed to close that loop.

There is also a deeper mystery the paper flags but cannot yet resolve: the sheer volume of chlorine production — up to 5 Gg per day — appears unexplained by any mechanism currently written into atmospheric chemistry models. That gap is not a weakness of the study; it's an invitation. The full paper in Nature Communications lays out the evidence transparently and calls for the modelling and observational work needed to answer it. In the meantime, this technique is ready to be applied to the next large volcanic eruption — or, more consequentially, to the first deliberate methane removal experiment conducted at scale.

• Formaldehyde as a methane tracer — Tracking HCHO from orbit gives scientists an ocean-compatible, real-time window into where and how fast methane is being chemically destroyed — something no existing satellite tool could do.
• A volcanic natural experiment — The Hunga Tonga eruption accidentally demonstrated, at planetary scale, what enhanced methane oxidation looks like from orbit, providing the first proof-of-concept for this detection methodology.
• The verification problem may be solvable — Future climate interventions that deliberately accelerate methane breakdown could now be independently monitored and verified using TROPOMI-class satellite observations, a requirement for responsible governance of any such programme.

"The sensitivity of our methodology can be sufficient for quantification in hypothetical future enhanced atmospheric methane oxidation approaches to help address future global warming." — van Herpen et al., Nature Communications, 2026.