Wednesday, 15 May 2013

The complexity of the diet and climate change debate

Post written by R. Cretney.

You are what you eat – or so the common saying goes. But as a global community are we what we eat? The issue of how our personal dietary choices effects social and environmental issues has long been a contentious issue. Considering the recent critique of  the undesirable impacts of quinoa’s popularity on poverty in Bolivia, it is understandable that many are left confused over what is the best choice, socially and environmentally. While the increase of organic, fair trade products has eased the social conscience of some, the issue of greenhouse gases, and in particular meat consumption, has proved a more tricky issue to deal with.

Some advocate that a world dominated by vegans and vegetarians is the only possible way to sustain the human population on a planet with finite resources. But what does the science say to support this?

Let us start with the issue of meat. As is quite well known, particularly in New Zealand, ruminant animals release Methane and Nitrous Oxide into the environment. These greenhouse gases (GHGs) contribute to our emissions profile as a country and as individuals. But is the complete elimination of meat and dairy products from our diets necessary?

A paper by Jennie MacDiarmid and others released in 2012 suggests otherwise. In this paper, the authors look at the optimum diet that maintains ideal standards of nutrition while maximising the possible GHG reductions in the United Kingdom. Food such as most vegetables, fruits and grains were considered low greenhouse gas emitters, certain fruits and vegetables, eggs, chicken, dairy products, nuts and sweet foods were considered moderate greenhouse gas emitters while red meat, turkey, cheese, pork and fish were considered high greenhouse gas emitters.

This backs up what many have argued, that red meat contributes significantly to our carbon footprints. But the issue is far from clear cut – the MacDiarmid (2012) article suggests that actually the most nutritious yet low GHG diet includes red meat but in smaller quantities than is currently consumed. Another recently released study by Darmon and others in the American Journal of Clinical Nutrition also suggested that moderation was key. This research studied the entire life cycle of the food and took into account all GHGs produced except those resulting from transport from the store to the home. The authors found that overall the emissions for meat products were 15 times that of fruit and vegetables. However, when taking into account the amount of energy in kilocalories that the food provided, meat products only emitted 3 times the GHGs as a comparable amount of energy derived from fruit and vegetables.

Darmon’s paper has been criticised by some proponents of vegetarianism who pointed out that most vegetarians do not eat the large quantity of vegetables that were used to compare emissions to a small portion of meat. Instead they argue that because they eat less vegetables than the nine pounds used, their carbon footprint is lower than the study suggests. Regardless, Darmon’s research is still useful, especially in combination with the MacDiarmid paper as both studies look into the increasingly grey area of the impact of our food choices on climate change.  

Here are some New Zealand figures that compare the GHG per kilogram of meat or milk solids as food for thought. The studies referred to before deal largely with European food production systems. As Saunders and MacDonald (2011) note, several types of meat production in New Zealand, such as lamb, are produced with much less emissions than those produced in Europe. This information shows that unlike the MacDiarmid study, New Zealand poultry and pork are actually low emitters (as opposed to moderate emitters in Europe) while sources of red meat are still high emitters. To put this data in context, a flight from Wellington to Auckland would release approximately 67.1kg of Co2 per passenger. The source of this data is the latest New Zealand legislation for emissions trading and the Air New Zealand carbon calculator.

Type of food
Kilograms of Co2 e/per kg at slaughter
(See Climate Change (Agricultural Sector) Amendment Regulations 2012 Legislation)
Sheep, Beef and Goat
Milk solids

While we may not be able to expect the entire world to become strict vegetarians, in the long run, a shift towards less red meat intensive diets could encourage a reduction in GHG emissions while acknowledging the importance of consuming meat for many economies and cultures. In the meantime there are less GHG intensive farming options to explore such as the adoption of more efficient farm management techniques. These options can be explored by farmers in New Zealand who will be able to market their products to those wishing to remain meat eaters while watching their carbon footprint (Clark et al 2011).

 Articles cited:

Clark, H.; F. M. Kelliher and C Pinares-Patino. 2011. "Reducing CH4 Emissions From Grazing Ruminants in New Zealand: Challenges and Opportunities", Asian-Australian Journal of Animal Science, 24:2, pp. 295-302.
Vieux, F., Darmon, N., Touazi, D., & Soler, L. G. (2012). Greenhouse gas emissions of self-selected individual diets in France: Changing the diet structure or consuming less?. Ecological Economics75, 91-101.
Macdiarmid, J. I., Kyle, J., Horgan, G. W., Loe, J., Fyfe, C., Johnstone, A., & McNeill, G. (2012). Sustainable diets for the future: can we contribute to reducing greenhouse gas emissions by eating a healthy diet?. The American journal of clinical nutrition96(3), 632-639. 
Saunders, C., McDonald, H., Driver, T. 2011. “Enhancing Value for New Zealand Farmers by
                        Improving the Value Chain”, Agribusiness and Economics Research Unit Report No. 324.


  1. I have one seemingly important comment on this week’s blog. There may be something worth clarifying or correcting.

    It seems to me that the emission factors in legislation are a very incomplete comparison to the other work you’re citing, with the worst case being the very low emissions for poultry. The ETS won't account for emissions associated with the product footprint that are already accounted for elsewhere, either in other countries or in the supply chain, right? So in the case of chickens, growing imported grain is likely to be accounted for in another country's inventory, or presumably somewhere else in the ETS even if feed is grown in NZ. Also, since fossil fuel emissions are accounted for at an obligation point somewhere else, these won't appear. The small emissions accounted for in the ETS are probably from excreta nitrogen, which indirectly produces nitrous oxide?

    Troy Baisden

  2. Can you please clarify how these emission factors are incomplete? I do not understand your analogy to grain growing. If, to raise 1 chicken to slaughter it produces x amount of CO2 equivalent emissions. Because a chicken will produce emissions during its life, then aren't the emissions of producing that chicken accounted for?

  3. Can you please clarify what you are trying to say? I do not understand what a product footprint a.k.a. an individual company-based (and possibly a marketing tool) has to do with emissions liability?

  4. Actually the emission factors are complete, in a sense that they utilize: industry data on energy, protein levels and other important components in animal feed up to slaughter, industry data on how the animals of grown up to slaughter and data on the amount of excreta produced over a lifetime of an animal. What this 'industry' data does not offer is what individual companies can do in terms of a carbon footprint. This is seen as more of a company specific marketing angle and rather not an 'across' the industry issue. So from this perspective - these are very complete.

  5. The emission factors in the table are New Zealand government factors for the potential inclusion of agriculture in the Emissions Trading Scheme not ‘industry’ data. As Troy Baisden points out they cover only methane and nitrous oxide emissions. Any use of fossil-fuel based energy within New Zealand to produce or transport feed (and any other part of the product life-cycle) would be covered elsewhere in the emissions trading scheme – in the part that is already active. If feed were imported, its emissions would not be fully covered. Thus these figures are not directly comparable to the Darmon or McDiarmid numbers for the US and Europe. We do not have equivalent full life-cycle numbers for poultry or pork.

    Suzi Kerr

  6. The data in the table are from industry. Please see the MAF reports - Dr. Fick

  7. Thank you for the clarification. I was not entirely sure if this was being said and I didn't want to assume. I agree that the factors presented in the table do not take into consideration the other components of meat production in the ETS, these may be picked up elsewhere (e.g. fossil fuels for transport, feed, etc). Feed procurement in NZ is very dependent on a number of issues (weather, sourcing location, amount required based on livestock numbers, etc). I don't think a 'set' number to determine a carbon footprint (or a full life cycle value) would be very realistic in NZ (based on feed procurement, production locations relative to supply chains, etc). But it could serve as a strong marketing tool (especially highlighting differences between nationally produced and internationally produced meats). I agree the numbers used for the Darmon or McDiarmid study are not comparable to the tabled numbers - as they serve a different purposes. However, if you follow, for example the poultry emission factor, it went from 0.8 to 0.5 now to 0.2 (kg co2/tonne of meat - the units in the table at least for poultry are wrong). There was scientific and industry based information reported to scientific and governmental panels in order to improve the NZ GHG inventory, which in turn also improved the ETS values.

  8. if I got my units wrong, they should be 0.2 tonne Co2/tonne of meat.


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