Much debate around food and its production is now concerned with sustainability. In Food Words, Matt Watson considers the complexities surrounding the ideas of sustainability and food, writing that food production accounts for up to a third of carbon emissions globally, but also noting that the sustainability of food is increasingly dubious, due to sensitivity of food systems to changes in climate and weather patterns. Clearly then, sustainable eating is far from straight forward, and requires us to consider both the impact of food systems on the environment (including carbon emissions) and the impact that environmental factors (and depleting resources) will have on our continuing ability to produce food. As such, achieving sustainability will require a deep understanding of the many and varied forces at play in food production. Grasping such complexity is a leviathan task, and beyond the scope of an article such as this. As such I will primarily be considering the environmental impact of food, notably carbon emissions.

It’s not news that there are big problems with our food system, and really big challenges facing us in the coming years. These issues have been receiving attention lately with the production of films like Farmageddon, and Cowspiracy. So for some time now, I have tried to eliminate meat from my own diet, and have been largely (though not entirely) successful. However, while avoiding meat I have begun to eat a lot more dairy (cheese is my staple snack) and eggs (at least 2 a day). As my intention was to adopt more sustainable and responsible eating habits, I’m left wondering if this shift from meat to dairy and eggs is negating the purpose of this change. After all, sustainability pressure groups often emphasise reducing dairy consumption (in addition to meat) as an important step towards environmentally friendly eating practices. However, I have heard little about eggs; intuitively it would seem that as animal products their environmental impact is likely high, but as I eat so many I think I should try and build a clearer picture.Eggs on a poultry factory

The environmental working group (an influential not-for-profit environmental advocacy group in the US) published a Meat Eaters Guide to Climate Change + Health, in which they calculated an average value of Co2 emitted per kilo of product. Based on data from two American egg producers, one “free-range” and one “factory-farm”, they calculated the average carbon emissions per kilo of egg to be 2.12kg (this is the figure for emissions at the farmgate – after production but before distribution and consumption). Interestingly they report the carbon per kilo to be nearly 22% less with the factory farmed eggs. This makes intuitive sense, as factory farming is designed to maximise outputs for a given input (although clearly other issues are associated with factory faming, such as animal welfare and routine antibiotic use). The Meat Eaters Guide, gives the figure for pork as 4.62kg Co2 per pound of pork, or 10.12kg/kg pork. Not surprisingly, I am doing better with my eggs (based on this metric alone) than if I ate bacon every morning! But could I reduce the impact of my consumption further? If I could stomach lentils for breakfast their Co2/kg is only 0.54kg/kg (at least these particular lentils from Idaho). And is this one metric telling the whole story? Where do these emissions come from, at what step in the chicken-egg-breakfast chain?

Rearing poultry on a large scale is not without its problems, such as ammonia produced when their faeces ferments, which can “significantly alter oxidation rates in clouds and enhance acidic particle species deposition (acid rain)” (Xin et al., 2011). Furthermore, high levels of ammonia in the chickens’ housing can hamper bird growth and egg quality, and make poultry more susceptible to disease. How chicken waste is managed is an important determinant of the quantity of ammonia produced, the wetter the waste, the more it ferments and thus the more ammonia. Xin writes that manure belt systems, essentially conveyor belts for chicken poo, produce significantly less ammonia than high rise housing (where waste simply drops down and is later cleared away manually), which in turn produces less than free-range rearing.manure-belt

Xin also states that in caged rearing systems that are well designed (for example, with good insulation), the metabolic heat of the poultry is sufficient to maintain an appropriate ambient temperature, and so no additional energy need be spent on heating. Other studies have also found benefits, in terms of sustainability, for intensive farming methods when compared to free range. De Boer and Cornelissen (2001) found that caged chickens were more sustainable than free range and Williams et al. (2006) reported that free range rearing, or organic rearing both independently increased the energy input required when compared to caged production by 15%.

In light of this information, two issues jump out. Firstly, there is the question of relative moralities.  I had assumed that free range, or organic food, was a more ethical choice, and some argue it is. But if the environmental footprint of intensively farmed chickens is significantly lower than that of free range and organic chickens and yet the welfare of caged animals is poorer, where does that leave the would-be ethical consumer? Should we prioritise environmental impact or is the increased level of emissions a fair price to pay for happy chickens? Secondly, we need to ask when does sustainability become meaningful? Maybe the production of my eggs resulted in 20% less emissions than your eggs, but is that difference really significant, or does it simply serve to make me feel better about my consumption patterns?

Clearly buying different eggs for breakfast isn’t change enough to ensure food security or environmental stability for the world of tomorrow. Any such change is only meaningful in the contexts of other, broader changes in society as a whole. And this is only a small piece of a very big picture; to be sustainable means far more than just lowering emissions, and far more than whether chickens are happy or not.