Food Chain Emissions


Friends of the Earth have sent our household a postcard. It says «The meat and dairy industry produces more climate-changing emissions than all the planes, cars and lorries on the planet.» They don’t quote a study, or any other source. Just a bold assertion which, on the face it, seems implausible. Even if you eat a gargantuan 250 g of meat a day (in other words, the typical US diet; Europeans eat about half that), does that really compare to all that driving round? It also seems a little bit mean to exclude trains and ships on the “transport” side. Is the balance between transport and food really so close that those 2 modes make all the difference? In the UK, rail and water account for about 4% of the total transport energy budget, so I would hope that the question isn’t so close that adding them back in tips the scales the other way. For one thing, any reasonable quantification of errors is bound to swamp that.

I think the FoE statement is false, here’s my homework.

David MacKay stacks up the UK’s energy consumption (Sustainable Energy – Without the Hot Air, Chapter 18, page 103), he has (per person): car 40 kWh/d, plane 30 kWh/d, food 15 kWh/d. So with 70 kWh/d (82 if we add the other transport modes) on the side of transport, and 15 kWh/d on the side of food then it does indeed seem implausible that food chain emissions would be higher. Note that we have all food production on one side, I can’t be bothered separating out meat from the rest, clearly meat forms the bulk of the energy consumption anyway. But wait…

As well as emissions related to the energy required to maintain the animals, they produce carbon-dioxide and methane all by themselves. In other words the food industry has emissions not related to its energy inputs (even if all the energy was produced sustainably, there would still be emissions). Non-energy related emissions show a weakness in David MacKay’s book; he neglects them completely. That’s okay, because his focus is Sustainable Energy, but be aware that it’s not the whole picture. Food, concrete, deforestation all have non-energy emissions. For animals I think we can neglect the CO2 emissions because the carbon originally came from the atmosphere anyway (respiration forms part of a close carbon cycle). Methane however is not negligible.

I reckon 1 kg of lamb produced between 60 g and 180 g of methane when it was walking about in the Peak District. That’s equivalent to about 2.4 kg of CO2. Let’s say I eat 100g of lamb a day. That’s (methane emissions equivalent to) emissions of 240g CO2, or about 1kWh of diesel. That’s roughly 0.1 litres; if you fill up 40 litres (about the size of my small car’s tank) every two weeks then that’s 3 litres a day. How often do you fill up? From a personal perspective, It looks like food-related methane emissions are not even close (to transport emissions).

Okay. So much for the ovine. What about the bovine, porcine, and, er, chickens? Well, I’m no veterinarian so this will take a lot of piecemeal research. Bugger that, lets go to a (competent?) summary: The UK’s Fourth National
Communication under the United Nations Framework Convention On Climate Change
. In 2004 UK agriculture (note: not just meat and dairy) emitted 13.8 MtC (megatonnes of carbon equivalent); transport emitted 37.4 MtC. Just what are these Friends of the Earth smoking that makes them think they can claim “The meat and dairy industry produces more climate-changing emissions than all the planes, cars and lorries on the planet” when it is so out of line with the UNFCCC GHG inventory. Is the UK really so atypical?

I suspect that what’s really happening is that the FoE are doing some clever accounting. There’s probably a little bit of double accounting (example, counting transport of feed on both sides), and I suspect some land use change. Perhaps they include chopping down ancient forest to grow soya beans for animal feed as an emission on the food change? I just don’t know, because they don’t show their homework. But I have a couple of points to make anyway. The first is that it’s not at all clear that the beef industry is too blame. If there was less demand for beef (and hence soya beans to feed the cows), then I think it’s likely that the same companies would have chopped down the same forest to grow something else. Miscanthus perhaps. The second is that while this land use change will be an emission (the UNFCCC recognises land use and land use change as a carbon source / sink), this emission occurs only once. Once the forest is cleared to grow soya, there will be no land use change emissions. So the emissions from the single land use change should be amortised over all future soya bean seasons. I think.

So FoE, how do you make the sums add up?

Appendix for the pedantic

«250g of meat a day … the typical US diet»

A quote from USDA Agriculture Factbook 2001-2002, Chapter 2, “Profiling Food Consumption in America”, :

“In 2000, total meat consumption … reached 195 pounds … per person”. That’s 242 g per person per day (2000 was a leap year).

«rail and water account for about 4% of the total transport energy budget»

Department for Transport, TSGB Chapter 3:

«1kg of lamb produced between 60g and 180g of methane»:

One 60 kg ewe produces about 20 litres methane a day (see below). Boned and trimmed meat is about 2/3 of the animal’s weight, so 0.5 litres / kg (boned). Lamb is generally defined as less than 12 month’s old or less than 18 month’s old for export. 360 days × 0.5 litres = 180 litres. × (the density of methane gas) 0.717 g/l = 129 g. 60 g to 180 g gives a range around this (to account for younger and older lambs, for one thing).

«one 60 kg ewe produces about 20 litres methane a day»

See Proceedings of the Nutrition Society, Volume 41, page 9A, meeting of 1981-07-17, “Methane production in lambs fed high- and low-roughage diets”. It depends on their diet: about 23 litres for high roughage; about 9 litres for low roughage. Two things: 1) when did you last see sheep being fed lucerne hay? 2) using 20 litres per day favours the FoE case anyway.

«equivalent to about 2.4 kg of CO2»

In terms of greenhouse gas warming potential, per kilo, methane is 20 times more potent than CO2. So 120 g methane equivalent to 2.4 kg CO2.

11 Responses to “Food Chain Emissions”

  1. Nick Barnes Says:

    If one removed food animals from the landscape, how would methane emissions change? Methane is produced by various processes of plant decay. It’s a detour in the carbon cycle: the carbon spends some percentage of the time as CO2 in the air, some percentage as cellulose in plants, some percentage as soil carbon, and some percentage as CH4 in the air. I have wondered before what these percentages are for various land uses (e.g. old-growth tropical rainforest, old-growth temperate forest, savannah, etc). How farm animals affect these percentages is an interesting and important question, but I don’t think it has an easy answer.
    [gagging at the thought of 250g of meat per day]

  2. David MacKay Says:

    “Methane is produced by plant decay anyway.”
    I wondered about this, and asked a plant / atmosphere expert at the Univ of Cambridge: does a conventional English garden (for example) emit methane because of decaying material, for example in compost heaps? Her answer was “No, negligible amounts. Methane-producing decay is possible, but only happens in unusual situations, eg when oxygen is excluded.”

  3. Gareth Rees Says:

    Friends of the Earth make this claim as part of their “Fix the Food Chain” campaign, where they say “The meat and dairy industry produces more climate-changing emissions than every plane, train and car on the planet – 18% of the global total.” and source the claim to “UN Food and Agriculture Organization”. They very unhelpfully give no link or detail of where their source was published.

    However, searching around on the FAO’s website finds this 2006 press release: “Livestock a major threat to environment” which says, “According to a new report published by the United Nations Food and Agriculture Organization, the livestock sector generates more greenhouse gas emissions as measured in CO2 equivalent – 18 percent – than transport.” The full report is supposedly available by FTP but when I downloaded it I only got the executive summary, not the detailed analysis. (Let me know if you find a full copy of the report anywhere, I’d like to read it.)

    Anyway, the summary of the FAO report makes it clear that it’s global livestock and global transport emissions that are being compared. Since I can’t read the full report I can’t do a sanity check of the calculations, but the FAO is a credible organization and I think it would be worth taking them seriously.

  4. Gareth Rees Says: comes to the rescue with the full text of “Livestock’s long shadow

  5. Clive Says:

    I don’t have any figures to hand, but it’s intuitively obvious to me that the UK is deeply atypical: we have such a high population density in the UK that we do very little livestock farming per head of population compared with, for example, Australia.

    And then there are less developed nations. What about China and India?

    Presumably the emissions cost for livestock has to include the energy involved in moving them around the countryside from farm to farm and farm to abbatoir, as well as the energy used in making and transporting their feed. Their figures don’t seem implausible to me.

  6. Gareth Rees Says:

    In the FAO report “Livestock’s long shadow”, the greenhouse gas analysis takes up pages 79–114. There’s a summary table on page 113. The analysis looks pretty solid to me (for example, the report notes that “Respiration by livestock is not a net source of CO2”).

    According to the FAO analysis, the largest single contribution that the rearing of livestock makes to climate change is deforestation, which as you (David) discuss above, is a one-off cost, and it’s arguable that it should be amortized over a longer period.

    Some climate change contributors that the FAO analyze that you omitted are: nitrous oxide, ammonia, methane release from manure, fossil fuel use in the manufacture of fertilizer, nitrogen emission from fertilizer, desertification and soil carbon loss (arguably one-off costs like deforestation).

    So I think the FOE claim on the postcard is good, at least up to arguments about how one-off costs like deforestation and desertification should be accounted for.

    • drj11 Says:

      Yeah, I found and skimmed this yesterday (the day after I wrote the artlcle, didn’t press publish until this morning). I agree their analysis is comprehensive (nitrogen was an epic fail on my part). But the report doesn’t seem very neutral. It’s written very much in the style of “here’s this bad thing, how can we attribute as much as possible to this bad thing”. So they run round and pick up a few million tonnes here, a few million tonnes there. Add it all up and you’re pretty soon talking serious emissions.

      I am still suspicious. For each emission they tend to find a reason to estimate in the high range for that category. This may be acceptable for a single case, but do it across the board and it starts to look like puffery. I’d like to see how it squares up with the national GHG inventories (which I am going to do next).

      And yes, it really does look like if boats and trains were added to transport then the FoE claim would be false. Which isn’t dishonest, but it really is drawing a line in the sand so you can complain about how little beach you have left.

  7. Gareth Rees Says:

    So I think the FOE claim on the postcard is good

    But since they failed to give a proper citation they still deserve a kick up the arse.

  8. Zeth Says:

    I hear this kind of anti-meat propaganda all the time. However, the traditional diet of meat and veg can be (and often is) grown locally. Whereas Lentils and Tofu and so on travel from Asia.

    Human Biology is still a young subject with many unknowns, and there are no doubt many subtle yet vital reasons why we evolved (and/or were created) to be omnivores.

    Since a far larger than normal amount of calories and protein are required to field an army, an ancient tactic to help prevent uprisings in newly conquered colonies was to prevent meat consumption for a few years. So the inner conspiracy theorist in me wonders whether we are all being brainwashed against meat in order to keep us weak and under control!

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