Shrinking dairy’s carbon hoofprint

After 10,500 years of farming them, does climate change mean we humans must limit our reliance on cows, or just change how we treat them? Image copyright fishhawk, used via Flickr Creative Commons licence.

After 10,500 years of farming them, does climate change mean we humans must limit our reliance on cows, or just change how we treat them? Image copyright fishhawk, used via Flickr Creative Commons licence.

Whenever I come across cows here in the southwest of the UK, usually placidly munching on a mouthful of grass, they always seem too lovable to be villains. But as we face growing twin challenges of feeding the world and fighting climate change, they’re increasingly getting a bad reputation.

Some scientists highlight reducing how much beef we eat, in particular, as an important step towards future sustainability. They say only about three or four parts in 100 of the energy in livestock feed becomes our food, while the rest is lost as manure, heat, digestive gases and slaughter by-products. Switching to more intensively farmed chicken or pork and plant-based food would be more efficient, the argument goes. It also gives a greater chance to trap carbon from waste material, which might otherwise become planet-warming greenhouse gases, as biochar that can help improve soil fertility.

A couple of years back I put this to Peter and Henri Greig who run my favourite local butchers, Pipers Farm. As they showed us round their farm Peter explained how their Red Ruby cattle can graze Devon moorland that can’t be used for crops, before moving on to pasture. While I still don’t eat a lot of beef for both environmental and health reasons, that seems a good reason for not demonising cows entirely. In fact, a paper in the June 2014 issue of the Journal of Dairy Science highlights previous research that found more grazing land exists, unusable for human food, than cropping land.

We can’t ignore what that promises for feeding the world in the future, but we can’t ignore cows’ greenhouse gas emissions either. However, rather than beef cattle, the new paper’s authors focussed on reducing levels of the potent greenhouse gas methane coming out of the digestive systems of dairy cattle. Joanne Knapp, a consultant who has researched nutrition in ruminant animals like cattle, told me her team’s interest comes in part thanks to its backers: Innovation Center for US Dairy.

Exhaustive research

Given that the Innovation Center’s stated aim starts ‘To increase demand for dairy products and ingredients globally’, the team’s motivation isn’t a surprise. “There’s a lot of emphasis on the burden from ruminant animals in terms of methane,” Joanne says. “The proportion of impact from dairy cattle and expectations on what can be done to mitigate that are sometimes overblown. However, we’ve shown that there are lots of different avenues to reducing emissions that already exist and can be combined.”

Around 22% of greenhouse gases resulting from human activity are linked to farming. But Joanne’s team emphasises that land use change, for example where forests are turned to farmland, is the largest part, responsible for around 15% of all human-caused emissions. The researchers also say dairy farming is responsible for little land use change, and that less than 2% of all human-caused emissions are thought to come from dairy animals.

(a) Estimated proportion of global methane emissions from natural and human-driven sources. The gas coming from cows and other ruminants is the segment labelled 'enteric fermentation'. (b) Global greenhouse gas (GHG) anthropogenic emissions by sector, with methane (CH4) and nitrous oxide (N2O) shown converted to volumes of CO2 that would give the equivalent 'global warming potential' (CO2e). (c) The 5 countries and regions with the largest livestock-associated enteric methane emissions on a million-metric-tonne (Mt)-of-CO2e basis. In the United States, 95% of enteric methane arises from ruminant livestock; this proportion can be assumed for other countries, although the contributions from beef versus dairy operations will vary. Manure methane is emitted by storage systems where anaerobic fermentation occurs. Manure methane and nitrous oxide can be from either ruminant or nonruminant livestock operations. EU 27 = European Union countries. Image copyright Elsevier, used with permission, see journal reference below.

(a) Estimated proportion of global methane emissions from natural and human-driven sources. The gas coming from cows and other ruminants is the segment labelled ‘enteric fermentation’. (b) Global greenhouse gas (GHG) anthropogenic emissions by sector, with methane (CH4) and nitrous oxide (N2O) shown converted to volumes of CO2 that would give the equivalent ‘global warming potential’ (CO2e). (c) The 5 countries and regions with the largest livestock-associated enteric methane emissions on a million-metric-tonne (Mt)-of-CO2e basis. In the United States, 95% of enteric methane arises from ruminant livestock; this proportion can be assumed for other countries, although the contributions from beef versus dairy operations will vary. Manure methane is emitted by storage systems where anaerobic fermentation occurs. Manure methane and nitrous oxide can be from either ruminant or nonruminant livestock operations. EU 27 = European Union countries. Image copyright Elsevier, used with permission, see journal reference below.

Although I was attracted to Joanne’s team’s research partly because of the opportunity for fart jokes, the methane cows produce is mostly not from farting. More of it comes out of their mouth, but even that’s not strictly burping, she stressed. Instead, thanks to how their four-stomached digestive system works, they simply breathe it out. Yet the impact of this natural process is no joke. Gas from the guts of livestock is responsible for 17% of all ‘human-emitted’ methane, and 3.3% of our total greenhouse gas emissions.

Long-life dairy

Our understanding of cows’ digestion therefore played a key part in several of the existing approaches to cutting methane emissions that Joanne’s team reviewed. Methane is produced as a by-product as microbes help ferment and, therefore, quickly break down plant matter in cows’ stomachs. Giving carefully balanced amounts of conventional feeds can control this biochemical pathway, to minimise methane and maximise milk production.

Other strategies include adding ‘rumen modifier’ substances to feed that suppress methane production, or trying to reduce the number of these ‘methanogen’ microbes. However these approaches aren’t straightforward as they can slow fermentation, and there are always other microbes ready to adapt and fill any newly-vacated niches.

Joanne’s team also focussed on other ways to boost the amount of milk produced by each cow, either by breeding or better care. One of the most important aspects of this idea was working to get cows producing milk for longer, starting them earlier and improving their health. “Total [methane] emissions will be decreased if annual production of milk remains constant and fewer cows are needed to produce the same amount of milk,” they wrote. In the UK, around a quarter of the methane produced by dairy cattle herds comes from replacement livestock.

Researchers in Argentina are trying to capture and reuse methane breathed out by cows. Credit: BBC

Yet they didn’t consider one method for reducing methane emissions that has attracted media attention – inflatable backpacks attached to cows that collect their digestive gases. Though Joanne acknowledged the Argentinian scientists who’d developed them have made useful research findings, she’s sceptical about their broader usefulness. “Equipment like that to collect methane from animals will be more expensive to make and maintain than what you’d make in return,” she said. “In the US there are nine million dairy cattle, nine million replacement heifers, and ninety million beef cows. Who’s going to maintain the equipment? Argentina’s much the same.”

Overall, Joanne’s team’s review makes the conservative estimate that combining these strategies can cut methane released per kilogram of milk by 15-30%. Europe and North America already exploit their potential, with intensive farming giving around five times as much milk for the amount of methane produced than more extensive approaches. “In India a cow produces 700kg of milk per year,” Joanne explained. “In Europe and North America, it produces 10,000kg. That’s where a lot of the environmental difference is. You can significantly decrease the impact of these animals when they’re more productive.”

Not cowed by limited support

Joanne Knapp's review of measures used to reduce dairy cattle methane emissions in practice highlights the importance of measures that also provide productivity and profitability benefits. Image copyright: Fox Hollow Consulting LLC

Joanne Knapp’s review of measures used to reduce dairy cattle methane emissions in practice highlights the importance of measures that also provide productivity and profitability benefits. Image copyright: Fox Hollow Consulting LLC

The direct financial benefit from better productivity is the main reason for farmers taking these steps, Joanne stressed, as other support for cutting emissions is scarce. “I’ve been working in this area for 25 years,” she recalled. “When I started out of university a lot of work was with the US Environmental Protection Agency, and I asked why they didn’t put money into it. There are now funds for capturing methane from manure, as the systems needed for that cost $80,000-$100,000.”

However carbon trading schemes in the US are beginning to help, Joanne added. “I’ve seen the annual budgets for some operations where they’re collecting methane from waste and manure,” she revealed. “If it were not for the carbon trading income those operations wouldn’t be financially solvent. Dairy farmers who do implement measures to reduce methane are getting credit for it. It hasn’t been an overwhelming burden.”

Yet we shouldn’t become complacent, as the Food and Agriculture Organization of the United Nations expects global dairy demand to be 58% higher by 2050 than it was in 2011. A quick calculation suggests that in that case methane produced per kilogram of milk would have to fall by 47% for overall dairy emissions to stay the same. That’s clearly more than Joanne’s team’s conservative estimate for possible reductions with existing methods. However, the consultant asserted that estimates they’ve worked on elsewhere show that a ‘very feasible’ 75% increase in milk production per cow could meet the 2050 target. It would do so with 11% fewer cows and the same methane emissions, manure excretion, and water usage as in 2010, she added.

Humans have farmed cows for around 10,500 years, long enough for the two species to shape each other’s development. To me, our society’s dependence on cows is comparable to its dependence on fossil fuels, and therefore changing our relationship with them could be similarly difficult. And while Joanne’s confident that the dairy industry can already make significant emissions cuts, she stressed that governments must ultimately ensure any actions are adequate. “A comprehensive review like ours will guide policy,” she underlined. “The industry is already implementing many approaches to reducing its environmental impact. Agriculture has been an easy target because there are benefits to profitability and productivity. It looks like a win-win-win and policies should be directed to that.”

Estimated maximum impact of various approaches to reducing methane emissions in intensive dairy production that have already been demonstrated to be effective in practice. The approaches are not expected to be fully additive, which is why the total maximum reduction is just 30%. Image copyright Elsevier, used with permission, see journal reference below.

Estimated maximum impact of various approaches to reducing methane emissions in intensive dairy production that have already been demonstrated to be effective in practice. The approaches are not expected to be fully additive, which is why the total maximum reduction is just 30%. Image copyright Elsevier, used with permission, see journal reference below.

Journal reference:
Knapp, J., Laur, G., Vadas, P., Weiss, W., & Tricarico, J. (2014). Invited review: Enteric methane in dairy cattle production: Quantifying the opportunities and impact of reducing emissions Journal of Dairy Science, 97 (6), 3231-3261 DOI: 10.3168/jds.2013-7234

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2 Responses to “Shrinking dairy’s carbon hoofprint”

  1. Jim in IA Says:

    Cows are an inefficient energy converter, it seems. The backpack methane capture system would require enormous cost and attention. I can’t imagine it ever being a workable product. I do see its importance as a research tool to better understand the role of the cow in methane production.

  2. Paul Price Says:

    Although it is good to see there is potential for improvement in agricultural emissions efficiency this discussion and apparently the research too omits mention of some critical points that I’ll try to make.

    Globally and for the long term, which are what matter for climate and for humanity’s future, the only measure that matters is ‘cumulative total emissions’ (CTE) as in IPCC WG1 SPM p27: “Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond (see Figure SPM.10).” In other words, the sum total of past, present and future emissions directly and linearly (within a confidence interval of course) determine the level of surface temperature increase.

    Emissions efficiency is ‘a good thing’ but only provided the savings in emissions and in costs made through ‘efficiency gains’ are never, ever ‘spent’ on more emissions somewhere, by someone, at sometime. To date this has never been the case: global wealth and annual emissions continue to increase exponentially, energy and emissions ‘savings’ are always spent on more consumption or on investing in aims of increasing consumption. Globally rebound is over 100%.

    The only way that all-time emissions-saving can be guaranteed is by an enforced, binding international agreement to constrain global CTE to a defined future limit. It is sad but true that bottom-up national, local or sectoral efforts are useless otherwise for the global and long term. Given the thousand year plus irreversibility of warming due to human-caused carbon emissions, emissions control really means that the whole point of efficiency is to buy time to enable global emissions to go to net zero as soon as possible, sources must balance sinks.

    The remaining CTE for all of humanity for the next thousand plus years is less than 1000 GtCO2 (still with a 1 in 3 chance of failing to limit warming to 2ºC). Currently annual global emissions are about 36 GtCO2 or 49 GtCO2eq. so the only realistic way of limiting warming is to get to zero net carbon globally as soon as possible while still feeding everyone sustainably into the future. Right now every year is stealing from the ability of all future generations to emit CO2 and other GHGs even for there food. Already the level of total system and behavioural change required to achieve a good chance of 2ºC is very high.

    It is important, I think, that any and every discussion of emissions efficiency makes the global and long-term ‘sufficiency’ context very clear up front, every time. This is because any discussion of individual national or sectoral policy has to happen within the context of a limited global atmospheric commons (as per WG3 TS p5). It is irrelevant whether a nation or a sector has a “low” share of global emissions (as above “less than 2%” of global emissions are from dairy). The question is: within the global CTE – for example for 2ºC, 66% chance – what is the least possible, equitable, necessary emissions from the nation or sector and how soon can they possibly achieve that given their current level of wealth and emissions?

    Every nation or sector has to state how they fit into a global plan to meet a CTE target in line with a stated chance of limiting warming to a stated and related temperature limit otherwise we are failing to plan and planning to fail. What share of the global CTE does their future likely emissions path imply? What share of the effort are they willing or able to take? And if unwilling or unable then what other sector has to take up the slack to provide a reduction or a sink to cover the sector’s excess emissions?

    For dairy the prominent claim is most often that increased emissions produced per litre of milk are a panacea as if that means we don’t have to multiply by the number of litres and then also by the number of all future years of emissions to assess the commitment to future warming due to dairy emissions. And then they actually have to meet the total emissions reduction claimed.

    Most importantly, loud claims of improving efficiency (past or future) are meaningless unless they actually do help humanity limit final CTE commitments to dangerous warming. We have to ask exactly how is it an ethical food emissions policy to commit to an increased beef and dairy sectoral CTE that will thereby produce an increased contribution to likely future food shortages due to heat stress and drought, especially in Africa, tropical Asia and around the Mediterranean? Witness, Syria and Iraq, already experiencing destabilising droughts that are exactly of the type and in places predicted to occur more frequently due to climate change resulting from human-caused emissions.

    One other point on agricultural emissions specifically, both the methane emitted and the fossil fuels used: ‘Feeding the world’s poor’ does not require more beef and dairy as the industry often claims, the main intended additional markets for increased anticipated production are wealthy consumers especially in new markets in rapidly developing countries like China. The fact is though that globally we cannot afford more meat and dairy either in energy input or in emissions output.

    We humans need food of course, but, given the CTE implications for climate damage and if there is any commitment at all to equity, as nations and sectors say they have, it is therefore critical to radically decrease emissions relative to total global nutritional need. It is very hard to see how that can be possible without massive waste reduction and a dietary shift away from dairy and animal meat consumption difficult though this is (see WG3 TS draft p 71).

    Are the beef and dairy researchers framing their research within this context? Is the dairy industry demanding a binding global agreement to limit CTE to 2ºC (or whatever temperature target is specified) to prevent carbon leakage and to push themselves and all sectors around the world to jointly achieve zero net carbon as soon as possible? Do they want to be part of a global or EU agri-ETS? If they are not answering these questions up front then we should be asking ourselves and them: Why not?

    IPCC WG1 SPM p17 spells it out:
    “Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.” This is a statement of the physical reality of the Earth’s climate system, not a negotiable policy point that can be ducked by individual nations or sectors claiming diminished responsibility on grounds of wishful thinking. The implication of the IPCC statement is simple: united we stand, divided we fall, effective action to limit future total is required.

    Somehow, collectively, among all nations and peoples, as they have already agreed at IPCC and in treaty declarations, we have to radically and urgently cut global emissions and maintain equity. Unless they show their emissions path in relation to the CTE and ºC limits for the decades ahead it is difficult to see how the beef and dairy industry’s plans for a very likely increase in their total emissions or global meat and dairy based diets fit into reality.

    Paul Price @swimsure


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