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	12.7kg
Milk solids	8.5kg
Poultry	0.20kg
Deer	21.0kg
Pork	1.76kg

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 Economics, 75, 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 nutrition, 96(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.

       Accessed From: http://www.motu.org.nz/files/docs/Saunders_McDonald_Driver_Value_Chain.pdf