One idea is likely to be in farmers’ climate toolbox sooner than either inhibitors or vaccines. Selective breeding with low-emitting bulls could reduce the methane outputs of the country’s dairy herd, which currently accounts for almost one-fifth of all of New Zealand’s emissions.

“We’re seeing 15 to 20% differences between low emitters and the average,” says McNaughton. “So I’m feeling quietly optimistic.”

Leahy agrees that the results appear promising, but notes there’s a lot more research and time needed to gather data. “There’s still a good bit of work to be done to verify the trait and make sure there are no adverse effects for breeding a low-emitting cow, for example on fertility,” she says.

Evidence from a US dairy cow herd suggests that low-methane cows might be smaller in stature with different gut bugs, but that their milk production and composition won’t be affected. Similarly, Irish cows that emit 15% less methane produce just as much milk for the same amount of feed, according to a study published this week.

At LIC, a similar investigation is underway with a new generation of daughters sired by the low-emitting bulls identified so far. The cows will be closely monitored for any adverse effects, such as reduced milk production.

By 2026, if no curveballs emerge, McNaughton expects that LIC and its competitor CRV will have a methane index for the bulls that sire 90% of New Zealand’s dairy herd through artificial insemination. This will mean that farmers can select bulls with lower methane profiles, among other desirable traits.

Selective breeding of low-methane dairy cattle rests on a foundation of sheep. While sheep emit, on average, 13kg of methane every year, compared to 98kg for a dairy cow, starting with sheep was a logistical choice. “Sheep are much easier to handle,” says Suzanne Rowe, senior scientist at AgResearch, “and their gestation period is much shorter.” Fourteen years ago, Rowe and a team of AgResearch scientists wondered whether a sheep’s methane emission levels could be passed from one generation to the next. They gathered 1,000 sheep from across New Zealand and began to measure their gas outputs over 48 hours using a respiration chamber.

“It took years to get through the 1,000 animals,” says Rowe, explaining the painstaking process to refine measurement down to just one hour instead of 48. The “huge challenge” yielded three incredibly useful things: a flock of low-emitting sheep, a flock of high-emitting sheep, and a portable unit for fast methane measurement.

The two flocks were relocated to the same farm in the South Island. High emitters bred with other high emitters, and lows with lows. Every year, Rowe and her team measured the methane outputs of the new lambs. And every year, the low emitters got lower by about 1%. Today the difference between the high and low flocks is, on average, 18%. Plus, the reduction doesn’t appear to come at the cost of other desirable traits – in fact, changes that have emerged so far are positive. “[Low-emitter] sheep had more wool,” says Rowe. “We also found that they have a slightly different fatty acid profile in their milk and meat, and were leaner.”

Meanwhile, the portable methane chamber has enabled farmers across New Zealand to identify the low emitters in their own flocks as part of a ‘Cool Sheep’ programme. “We’ve been driving up and down the countryside, measuring sheep from different farms,” says Rowe, estimating that they have now measured 30,000 individuals. “The plan is to enable farmers to choose the low emitters within their own flocks,” Rowe explains. “That’s really important because it means that the animals they choose are already adjusted to that environment.”

What impact will selective breeding have on New Zealand’s methane emissions? For sheep, Rowe estimates a decrease in methane emissions of around 0.5 to 1% per year. “Over time, that quickly becomes substantial,” she says. “The other benefit is that, other than the actual measurement of the animal, it’s low cost. And it’s permanent.” But the impact of selective breeding is also slow to emerge, as genes filter through a population over time rather than acting instantaneously.

In Canada, low-methane bull semen became commercially available earlier this year. Semex, the company behind the genetics, says adoption of the low-methane trait could reduce Canada’s dairy herd emissions 20–30% by 2050.

New Zealand’s numbers are more conservative. In 2021, modelling by the country’s Climate Change Commission suggested that low-methane breeding for sheep and beef cows would produce 4.5–7.5% reductions by 2050. For the dairy cattle herd, breeding is predicted to come online from 2030 and yield a 7.5–13.5% methane reduction by 2050.

Behind the incremental march of scientific efforts, the spectre of a price on agricultural emissions looms large. New Zealand’s first attempt at introducing an agricultural emissions levy dates back to 2003, when a ‘fart tax’ furore erupted. ‘Fart tax’ is a misnomer, says Leahy, as most gases are expelled out the front end: “about 75:25 nostrils to mouth”.

The proposed levy would have raised NZ$8.4m (£3.1m or US$4.9m) per year for research. Vehement opposition to the idea saw one MP drive a tractor up the steps of parliament, and another lead two cows around parliament grounds, with one depositing a steaming cowpat in front of the parliament.

Since then, the agriculture sector has lobbied hard to avoid being roped into New Zealand’s emissions trading scheme, making it an outlier industry that doesn’t pay a price for its climate pollution.

In 2017, Jacinda Ardern, who had campaigned on a promise to bring farming into the ETS, unexpectedly became prime minister. The farming sector secured a deal with the government to co-design a separate pricing scheme in a partnership called ‘He waka eke noa‘ (named after a Māori proverb, meaning “we’re all in this together”). In advice delivered during the design process, New Zealand’s Climate Change Commission said that “a farm-level pricing system, supported by well-designed, well-thought-through policy” is an important tool for achieving the country’s climate targets.

In the final plan, announced in December 2022, the government would set different five-year prices for methane, nitrous oxide and carbon dioxide, with input from farming representatives and the Climate Change Commission. The scheme was meant to come into effect in 2025, but by mid-2023 the plan had fallen over. A new centre-right coalition is likely to see any potential pricing of cow burps pushed back to 2030.

Suzi Kerr, a New Zealand economist with expertise in emissions pricing policy, says the delay is “going to be really damaging when they have to hurry to catch up later.

“Hurrying to catch up is costly, it’s difficult,” she says.

According to Kerr, an agricultural pricing scheme wouldn’t just benefit the climate, it would also help New Zealand farmers by providing consistent market signals and a mechanism to reward them for their climate action.

“Farmers are in this invidious position of knowing what they should be doing from a global point of view, but facing really strong economic signals that are saying ‘produce more’ and don’t focus on mitigation. Pricing levels that playing field,” says Kerr.

Without a pricing scheme, will New Zealand be able to reach its methane reduction targets? “New Zealand’s history would suggest no,” says Kerr.

In 2021, emissions from the agriculture sector dipped by 1.5%, in part due to fewer sheep and cattle. But it’s a tiny blip after almost a decade of a stubborn plateau, and not necessarily enough to indicate a new trend, says Kerr. “Improvements in lowering emissions have been offset by increased levels of production,” she says. “Even if they’re beginning to fall in some places, they’re not falling nearly fast enough.”

In advice released this week, the Climate Change Commission warned that New Zealand is not on track to meet its overall emissions reduction targets. For methane, the commission writes: “Existing policies alone… would not result in adequate biogenic methane reductions to meet the 2030 target.”

In order to achieve a 10% methane reduction by 2030 and reach the longer-term 2050 target, the commission emphasised that agricultural emissions pricing from 2025 will be “key” and a “necessary tool”. New tech, diversifying land use, and increasing on-farm efficiency will also play a role in the 2030 target, according to the commission.

Breeding low-methane animals, along with the development of methane inhibitors and vaccines, will help New Zealand meet its long-term climate goals, the commission notes.

The analysis was conducted in October 2023, before the election resulted in a change of government and new policy direction. While the new climate change minister welcomed the advice and has affirmed the government is “steadfast” in its commitment to the Paris Agreement, several keystone climate policies are set to be discarded or delayed – like the agricultural pricing scheme. The shift has attracted criticism from environmentalists for relying on technological works-in-progress, rather than proven interventions to reduce agricultural emissions. It will be up to the new government whether they heed the commission’s advice.

If the country fails to meet its agreed emissions reduction targets under the Paris Agreement, it may need to spend billions of dollars on overseas carbon credits to offset its climate pollution, including the methane-laced breath of farm animals.

Leahy says reducing methane in line with the official targets will be “challenging”. But she remains optimistic. She used to give presentations and tell the audience that she wasn’t even sure it would be possible to reduce the methane brewed in an animal’s gut. “Fast forward to today, and yes, there is sheep breeding, yes, there are inhibitors, yes, there are some feeds. These are all coming. And hopefully more,” she says.