From Seaweed to Climate Solution: How Asparagopsis Reduces Methane in Livestock

It was in 2016 when a peer-reviewed article on an in vitro trial involving a species of red seaweed made waves in the global scientific community. The discovery that this naturally occurring algae could reduce methane emissions in ruminants by an almost unbelievable magnitude spread quickly, much like the seaweed itself.

Suddenly, Asparagopsis was being talked about as one of the most promising solutions to agricultural greenhouse gas emissions. Give a “certain amount” of this “magical” seaweed to cows, and methane emissions drop by 40%, 60%, 80%, even up to 99% in some controlled trials. The headlines spread fast, and where sensational claims appear, so do questions and critics.

Some studies raised concerns about animal health, feed safety, and potential trace compounds in milk. So where does that leave us?

In this article, we’re going to take a clear-eyed look at Asparagopsis: what makes it so special, what the science actually shows, what challenges remain, and why Seaweedland believes this 

seaweed can play a crucial role in building a more sustainable future.

Asparagopsis is a genus of red macroalgae consisting primarily of two species: Asparagopsis armata and Asparagopsis taxiformis. A. armata is most commonly found in cooler, temperate coastal waters, whereas A. taxiformis prefers warmer, subtropical and tropical environments. One of the features that makes Asparagopsis visually distinctive is its soft, wool-like external texture, which sets it apart from more leaf-like seaweeds such as Ulva and Dulse.

What truly makes this red seaweed remarkable, however, is a unique biochemical trait. Asparagopsis naturally produces halogenated methane analogues, the most notable of which is bromoform (CHBr₃). These compounds play a role in the seaweed’s defense against grazing marine organisms but, as research has shown, they also interact in a very specific way with the methane-producing microorganisms inside the stomachs of ruminants. This is where the story becomes particularly interesting for climate impact.

Bill Gates once said, “If cattle were a country, they would rank third in greenhouse gas emissions.” That statement remains painfully accurate. The reason lies in the chemistry of methane (CH₄). In the short term, methane is significantly more dangerous than CO₂: over a 20-year period it traps around 80 times more heat, making it one of the most potent drivers of rapid warming. Although methane breaks down faster than CO₂, this short lifespan actually creates an opportunity. Cutting methane emissions can deliver immediate climate benefits, slowing warming within decades rather than centuries, making it one of the most powerful levers we have to meet globally-set short-term climate targets.

As ruminants digest feed, fibre is broken down by microbes in the rumen (the first stomach). These microbes produce hydrogen (H₂) and carbon dioxide (CO₂), and a special group of microorganisms called methanogenic archaea convert these into methane (CH₄), which is then released mainly through belching.

Here’s where bromoform comes in. When cattle are fed even a small amount of Asparagopsis (typically 0.15–0.50% of their diet), bromoform disrupts the methane-forming pathway, and the hydrogen is redirected into alternative fermentation routes. As a result, methane production drops significantly.

Laboratory studies often show 80–95% reductions in methane emissions, while on-farm or feedlot trials generally report reductions in the 30–60% range. This difference exists because lab systems are controlled and stable, whereas the rumen is a dynamic ecosystem that constantly adapts to diet and microbial shifts. But the direction of the findings is remarkably consistent. Whether in the lab or in the field, Asparagopsis repeatedly demonstrates a substantial and meaningful reduction in methane emissions.

There is no scientific progress without critical voices. Some studies have raised concerns about trace levels of bromoform appearing in the milk of cows fed Asparagopsis. Bromoform breaks down quickly in the human body, but high amounts could affect the liver and thyroid, so the concern is understandable. The key point is that scale matters. The studies that detected bromoform used relatively high inclusion rates of Asparagopsis, far above what is needed for methane reduction. Most research shows that very small amounts (approximately 0.15–0.50% of the diet) are enough to achieve significant methane reductions without detectable bromoform in milk or meat.

When we zoom out and look at the bigger picture, the potential of Asparagopsis is gargantuan. With controlled and responsible use, it has the power to drastically reduce one of the leading causes of global warming, while requiring remarkably few resources: no freshwater and minimal arable land. But we have to stay realistic: Asparagopsis is not a one-stop solution. Methane hits the climate like a flash fire, while CO₂ fills the atmosphere like a slowly rising tide. Cutting methane emissions delivers immediate climate benefits within decades, whereas reducing CO₂ is essential for long-term stabilization. Ongoing critique and careful testing are what move the science forward, ensuring that this solution remains both effective and safe.

At Seaweedland, we believe strongly in the potential of Asparagopsis as a powerful climate solution, especially for rapidly reducing methane emissions. Through our Bromin project, supported by a Dutch government R&D subsidy, we are advancing the science behind methane-reducing Asparagopsis and developing cultivation methods that maximise quality and bromoform content in a safe, consistent way. Our land-based, fully controlled cultivation system enables stable, year-round yields with zero contamination risk, overcoming the limitations of ocean farming. And we’re not alone: more innovators worldwide are turning toward on-land cultivation of micro- and macroalgae. Together, we’re making waves toward a cleaner, more sustainable future.