An aggressive reduction in methane emissions from beef and dairy herds is achievable, Professor Mitloehner argues, taking cattle farming beyond climate neutrality and setting it up to help offset emissions from other sectors.

Professor Frank Mitloehner, an air-quality specialist in the department of animal science at University of California, Davis, doesn’t much like it when critics accuse him of glossing over the greenhouse gas (GHG) emissions challenge that methane (CH₄) represents. He likes it even less when they accuse him of greenwashing, as he made clear at the ‘Methane Forum In Livestock’ event that packer and tanning group JBS and leather chemicals group Silvateam hosted in São Paulo in May, where he was one of the keynote speakers.

“I don’t want anyone to think I’m saying that methane doesn’t matter,” Professor Mitloehner insists. “It does matter. It is a potent greenhouse gas whose impact we are working hard to reduce.”

Blanket coverage

Going back to GHG basics, he explains that these gases form a blanket over the atmosphere and retain the heat that comes from the sun, heat that we need to make it possible to grow the food we eat and to live. “Without greenhouse gases, life on earth would not be possible,” he says. “But the problem is that human activity is putting out too many greenhouse gases and the blanket is becoming too thick, and that means too much heat from the sun is being retained.”

Most climate scientists accept that the most important greenhouse gas is carbon dioxide (CO₂), according to the professor. Even so, there are people (some of them quite loud) who are not keen on the livestock, meat and leather sectors and who want the climate-change debate to concentrate much more on methane instead. Comparisons can be tricky, made no less tricky by the matrix called GWP 100. The letters stand for ‘global warming potential’ and the number comes from the time period over which the matrix aims to measure the warming effect of different gases.

Devil in the detail

GWP 100, which was designed to help policy makers understand how different sectors compare, and has been in use for 30 years, tells us that methane is 28 times more powerful than CO₂ in trapping heat from the sun. “This is true,” Frank Mitloehner says, “but it leaves out a very important detail, one that helps us understand that methane acts differently. It isn’t as simple as saying that a farm that emits 10 tonnes of methane emits 280 tonnes of CO₂-equivalent. Methane is much more nuanced than other greenhouse gases.”

All sources of CH₄, globally, produce around 560 teragrams per year. One teragram is equal to 1 billion kilos. This, the professor insists, is where most reporting about methane stops, but it ought not to be. There are sinks for methane, the greatest of which is from chemical reactions that occur in the atmosphere. “There are so-called radicals,” he explains, “and when they meet methane, they destroy it.”

Another important carbon sink is soil carbon capture, which refers to plants pulling carbon from the atmosphere and storing most of it below ground, in their roots. Thanks to these two sinks, around 550 of the 560 teragrams of methane produced are destroyed. If you subtract one from the other, you end up with a net amount of 10 teragrams of methane. Frank Mitloehner calls this “still a number that we need aggressively to reduce”, but one that is grossly different from just looking at the volume of methane produced.

Destroyed, in this discussion, means that the methane is no longer methane; it becomes something else: CO₂ and water. How long does this take? About a decade, which means methane has a very different lifespan compared to CO₂. The professor talks in terms of half-life: 10 years for CH₄; 1,000 years for CO₂, illustrating clearly, he says that they are different types of gas. So different that CH₄ represents an opportunity to collect and use valuable energy, an opportunity, he points out, that dairy farmers in his home state, California, are already grabbing by the horns. More on this below.

No new carbon

Another constant theme in Frank Mitloehner’s narrative is that a constant cattle herd size will add no new carbon to the atmosphere. Ruminants recycle carbon. This starts with photosynthesis, which converts CO₂ from the atmosphere into carbohydrates in the form of cellulose or starch. The methane that the ruminants emit into the atmosphere is carbon that used to be in the atmosphere anyway in a different form; it was CO₂ and now, for ten years, it is CH₄. It is what he calls “a short-lived cycle”. If the herd size stays the same, this methane will cause no additional warming to the planet.

The same is not true of carbon from fossil fuels. “Practically all the fossil carbon,” the professor continues, “was underground until relatively recently, until human beings began to extract it and burn it. This is not a short-lived cycle; it’s a one-way street. What took thousands of millions of years to accumulate, we have taken out at record speed. That’s why we see increases in CO₂ levels, year after year. This matters because, once we put the CO₂ into the air, it’s there for 1,000 years.”

An analogy he likes centres on a person who lives 20 kilometres from work and travels to and from there by car. Every day, on every trip, throughout that person’s working life, new CO₂ goes into the atmosphere and stays there for a millennium. “The driver keeps adding to existing stock of carbon,” he explains. “That’s why CO₂ is called a stock gas. Currently, methane is treated as though it were a stock gas too, as if every time an animal belches it were adding new, additional carbon to the atmosphere, but it isn’t. CH₄ is not a stock gas. It is a flow gas because it’s not just produced, it’s also destroyed.”

Overflow

Another example he gives is of a fossil fuel-fired power-plant. If it runs with a constant output for 30 years, it will keep emitting CO₂ and keep causing additional warming. If, after 30 years, the power-plant is decommissioned, there will be no further emissions from it and no further additional warming, but the warming effect that the emissions from the facility built up over three decades will remain for a millennium; it will plateau, but it will not go down, unlike the warming effect caused by methane, which will last a decade.

Lastly, he likens GHGs to a bathtub. In the case of CO₂, the tap is running and the bathtub has no plughole to drain water away and, therefore, the volume can only increase. With CH₄, the tap is running, but there is a plughole to remove some of the water from the bathtub and for it to flow into the drain. If the water comes out of the tap at the same rate as it drains away, the volume in the tub will remain constant.

He says once more that this does not mean that CH₄ is “unimportant”. It is important, just different, the professor insists. But GWP 100 mischaracterises it, with the professor of geosystem science in the school of geography and the environment at the University of Oxford, Myles Allen, calculating that GWP 100 overblows methane’s impact by a factor of four, if the source of the methane is constant. Professor Allen, a lead author of reports for the United Nations’ Intergovernmental Panel on Climate Change (IPCC), has come up with his own matrix, GWP*, which takes the same values and interprets them in a different way to focus on “warming-equivalent emissions”.

Professor Mitloehner’s conclusion is that there is a keen need for measuring GHGs in a way that is fit for purpose, measurements that “do the job well”. He is in no doubt that GWP 100 fails to fulfil this criterion, and says, exasperatedly: “And yet it’s GWP 100 that people have been using for beef and for dairy for the last 30 years.”

Faster removal

To return to the bathtub analogy, he points out that there are, as mentioned above, moves afoot to remove methane at a quicker rate than a cattle herd of consistent size can emit the gas. In California, there is a new law, Assembly Bill 197, that mandates by 2030 a reduction of 40% in methane levels compared to 1990. “Farmers went wild at first,” the professor says, “but the legislators have made it clear that they want to help them find solutions too, which is to say provide funding for developments that will aggressively reduce methane levels.”

This is already bearing fruit, he explains. The solutions to have come to light so far focus on manure; solutions focusing on methane from enteric fermentation will follow. For manure, anaerobic digestors have allowed farmers to build up covered “carbon lagoons”, in which 60% of the gas is CH₄. The trapped gas is being converted into renewable natural gas that is being used as a partial replacement for diesel, with the farmers receiving rich rewards for this work. “Some of the farmers have said they are now making a half or a third of their income through this,” Frank Mitloehner says.

After only a couple of years, this has already led to a 25% reduction in methane emissions from the California dairy industry. When reductions in methane from enteric fermentation follow, the dairy industry will achieve the 40% target, Professor Mitloehner insists, adding that teams at the University of California, Davis, have already experimented with dozens of different feed additives too. He has been encouraged by the results so far: two-thirds of the feed additives have done nothing to alter methane levels from belching, but between five and ten of the additives tested by researchers at the university have resulted in reductions.

Climate neutrality and beyond

 All of this, he contends, will help the dairy industry achieve climate neutrality, reducing methane by an impressive enough level to achieve what climate scientists call ‘negative warming’, also known as cooling. And the professor says dairy farmers can go even further, providing offsets for the warming caused by other greenhouse gases. “After reaching climate neutrality, the farmers will be able to claim additional carbon credits that they can sell to other sectors, including the fossil fuel sector,” he continues. “This is already happening; I have seen Shell, BP, BMW and others buy credits from dairy farmers.”

He points out that food waste and food loss remain the biggest contributors to the wider food system’s overall carbon footprint, with a share of 40% of the total. But while it is not true that reducing methane will “save the world from climate catastrophe”, the beef and dairy sectors are correct to be as committed as they are to lowering methane emissions from cattle. He concludes: “I am very bullish about this. We can use the best science available and aggressively reduce methane. The fossil fuel industry cannot do what we can do.” 

Frank Mitloehner at the University of California, Davis.
Credit: UC Davis

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