In the world of climate and energy, “emissions” is often shorthand for carbon dioxide, the most abundant anthropogenic greenhouse gas in the world. Similarly, talk of emissions capture and removal usually centers on the growing swath of technologies that either prevent CO2 from entering the atmosphere or pull it back out after the fact.
Discussions and frameworks for reducing methane, which is magnitudes more potent than CO2 in the short-term, have been far less common — but the potential impact could be huge.
“If you can accelerate the decrease of methane in the atmosphere, you actually could have a much more significant climate impact, much faster than with CO2,” Gabrielle Dreyfus, chief scientist at the Institute for Governance & Sustainable Development, told me. “People often talk about gigatons of CO2 removal. But because of the potency of methane, for a similar level of temperature impact, you’re talking about megatons.”
Over the past year or so, this conversation has finally started to gain traction. Last October, the National Academies of Sciences, Engineering, and Medicine released a report on atmospheric methane removal, recommending that the U.S. develop a research agenda for methane removal technologies and establish methodologies to assess their impacts. Dreyfus chaired the committee that authored the report.
And one startup, at least — Denmark-based Ambient Carbon — is trying to commercialize its methane-zapping tech. Last week, the company announced that it had successfully trialed its “methane eradication photochemical system” at a dairy barn in Denmark, eliminating the majority of methane from the barn’s air. It’s also aiming to deploy a prototype in the U.S., at a farm in Indiana, by year’s end.
The way the company’s process works is more akin to point source carbon capture, in which emissions are pulled from a smokestack, than it is to something like direct air capture, in which carbon dioxide is removed from ambient air. Inside a dairy barn, cows are continually belching methane, producing high concentrations of the gas that are typically vented into the atmosphere. Instead, Ambient Carbon captures this noxious air from the barn’s ventilation ducts and brings it into an enclosed reactor.
Inside the reactor, which uses electricity from the grid, UV light activates chlorine molecules, splitting their chemical bonds to form unstable radicals. These radicals then react with methane, breaking down the potent gas and converting it into CO2, water, and other byproducts. The whole process mimics the natural destruction of atmospheric methane, which would normally take a decade or more, while Ambient Carbon’s system does it in a matter of seconds. Much of the chlorine gets recycled back into the process, and the CO2 is released into the air.
That might sound less than ideal. Famously, carbon dioxide is bad. This molecule alone is responsible for two-thirds of all human-caused global warming. But because methane is over 80 times as potent as CO2 over a 20-year timeframe, and since it would eventually break down into carbon dioxide in the atmosphere anyway, accelerating that inevitable process turns out to be a net good for the climate.
“The amount of CO2 produced by methane when it oxidizes has about 50 times smaller climate effect than the methane that produced it,” Zeke Hausfather, a climate scientist and climate research lead at Stripe, told me. “So you get a 98% reduction in the warming effects by converting methane to CO2, which I think is a pretty good deal.”
As he sees it, preventing methane emissions in the first place or destroying the molecules before they’re released, as Ambient Carbon is doing, is far more impactful than pursuing after-the-fact atmospheric methane removal. Because while CO2 can linger in the air for centuries — making removal a necessity for near-term planetary cooling — when it comes to methane, “if you cut emissions, you cool the planet pretty quickly, because all that previous warming from methane goes away over the course of a decade or two.”
Agriculture represents 40% of global methane emissions, the largest single source, making the industry a ripe target for de-methane-ization. Ambient Carbon’s tech is only really effective when methane concentrations are relatively high, the company’s CSO, Matthew Johnson, told me — which still leaves a large addressable market given that in many parts of the world, cows are mostly kept in dairy barns, where methane accumulates.
In its trial, Ambient Carbon’s system eliminated up to 90% of dairy barn methane at concentrations ranging from 4.3 parts per million to 44 parts per million. But while the system can theoretically operate at the lower end of that range, Johnson told me it’s only truly energy efficient at 20 parts per million and above. “It’s a question of cost benefit, because we could remove 99% [of the methane from dairy barns] but if you do that, that marginal cost is more energy,” Johnson explained, telling me that the company’s system will likely aim to remove between 80% to 90% of barn methane.
One reason methane destruction and removal technology hasn’t gained much traction is that capturing methane — whether from the atmosphere, a smokestack, or a ventilation duct — is far more challenging than capturing CO2, given that it’s so much less prevalent in the atmosphere. Atmospheric methane is relatively diffuse, with an average concentration of just about 2 parts per million, compared with roughly 420 parts per million for CO2. “I heard the analogy used that if pulling carbon dioxide out of the atmosphere is finding a needle in a haystack, pulling methane out of the atmosphere is pulling dust off the needle in that haystack,” Dreyfus told me.
Because of methane’s relative chemical stability, removing it from the air also requires a strong oxidant, such as chlorine radicals, to break it down. CO2 on the other hand, can be separated from the air with sorbents or membranes, which is a technically simpler process.
Other nascent approaches to methane destruction and removal include introducing chlorine radicals into the open atmosphere and adding soil amendments to boost the effectiveness of natural methane sinks. Among these options, Ambient Carbon’s approach is the furthest along, most well-understood, and likely also lowest-risk. After its successful field trial, “there is not much uncertainty remaining about whether or not this does the claimed thing,” Sam Abernethy, a methane removal scientist at the nonprofit Spark Climate Solutions, told me. “The main questions remaining are whether they can be cost-effective at progressively lower concentrations, whether they can get more methane destroyed per energy input. And that’s something they’ve been improving every year since they started.”
Venture firms have yet to jump onboard though. Thus far, Ambient Carbon’s funding has come from agricultural partners such as Danone North America and Benton Group Dairies, which are working with the company to conduct its field trials. Additional collaboration and financial support comes from organizations such as the Hofmansgave Foundation, a Danish philanthropic group, and Innovation Fund Denmark. Johnson told me the startup also has a number of unnamed angel investors.
Whether or not this tech could ever become efficient enough to tackle more dilute methane emissions — and thus make true atmospheric methane removal feasible — remains highly uncertain. Questions also remain about how these technologies, if proven to be workable, would ultimately be able to scale. For instance, would methane destruction and removal depend more on government policies and regulations, or on market-based incentives?
In the short term, voluntary corporate commitments appear to be the main drivers of interest when it comes to methane destruction specifically. “A lot of food companies have made public pledges that they’re going to reduce their greenhouse gas emissions,” Johnson told me. As he noted, ubiquitous brands such as Kraft Heinz, General Mills, Danone, and Starbucks have all joined the Dairy Methane Action Alliance, which aims to “accelerate action and ambition to drive down methane emissions across dairy supply chains,” according to its website.
The way Ambient Carbon envisions this market working, its food industry partners would be the ones to encourage farms to buy the startup’s methane-destroying units, and would pay farmers a premium for producing low-emissions products. This would enable farmers to cover the system’s cost within five years, and eventually generate additional revenue. Whether the food companies would pass the green premium onto consumers, however, remains to be seen.
But as with the carbon dioxide removal sector, voluntary corporate commitments and carbon crediting schemes will likely only go so far. “Most of what’s going to drive methane elimination is going to be policy,” Hausfather told me. Denmark, where Ambient Carbon conducted its first trial, is set to become the first country in the world to implement a tax on agricultural emissions, starting in 2030. Europe also has a comprehensive greenhouse gas reduction framework, as do states such as California, Washington, and New York.
“It’s such a low-hanging fruit of climate impacts that it’s hard to imagine it’s not going to be regulated pretty substantially in the future,” Hausfather told me. But stringent regulatory requirements are often shaped by the technologies that have been established as effective. And in that sense, what Ambient Carbon is doing today could help pave the way for the ambitious methane targets of tomorrow.
“Moving from a lot of the voluntary pledges that we have towards more mandatory requirements I think is going to have a really important role to play,” Dreyfus told me. “But I think it’s going to be easier if we have more proven technologies to get there.”
