Let them fart
I was doing some research the other day on the ecological footprint of various natural fibers used in the garment industry, when I stumbled upon an article mentioning the effects on climate change caused by the gases released during digestion of grass-feeding animals, such as sheep and other ruminants. It was actually implying that because of this, wool was not as terrific a material from an ecological point of view, as was commonly thought.
At first, to tell you the truth, I pondered this was the farfetched work of some sarcastic and inventive lobbyist for the plastic industry. He was probably trying to confuse the public by blowing a smelly veil of smoke on their own dirty business of polluting the earth. This well documented technique originated with the tobacco industry, and has flourished in environmental issues since then. However, as it still rather piqued my interest, I read that article to the end, and went on to dig further into the subject.
The technical name for this flatulence problem is “enteric fermentation”. It accounts for the gases generated during the digestive process of ruminants. Although non-ruminants species also produce them when digesting, the amount is much lower.
Moreover, the undisputed scientific fact that this article was mentioning is that methane – the chemical nature of the gas - is 25 times more damageable to the climate than CO2. There was indeed something to it, and I had to get to the bottom of it, if I may say.
Carbon dioxide equivalent
I found out that to simplify the comparison between various greenhouse gases, the scientific community use formulas to express them in CO2 equivalents, or “CO2e”, as carbon dioxide is by far the main and most common gas responsible for global warming. In our case, when we look at 1 ton of methane emissions, we will transpose it into 25 tons of CO2e.
The numbers we have are those compiled by the Food and Agricultural Organization, a UN agency, and specifically its Global Livestock Environmental Assessment Model (GLEAM). Their latest complete datasheet is from 2014.
Looking at those figures, we can see that the world’s total emission of CO2e was 49.44 billion tons for that year. Of these, the part that was attributable to agriculture was 11%, or 5.68 billion tons CO2e.
Ruminants, small and large
This figure is segmented in various categories. The one representing the enteric fermentation we are looking at, amounts to 40%. The livestock responsible for the most emission within those 40% is by far cattle, with 62% of the total, while we can split the rest between pork, chicken, and the category that interests us: small ruminants. Those are mainly sheep and goats, forming approximately evenly numbered livestock, and they account for 7% of the total enteric fermentation.
Calculating the specific contribution of the enteric gas emissions of sheep is therefore a straightforward mathematical process: 7% of 40% of 11%, then divide by 2 in order to account for the goats. The result is 0.154%. In other words, the greenhouse gas emissions attributable to the methane released by sheep are a mere 0.15% of the total CO2e produced in the world.
Of course, we all know that small streams make large rivers, and we should not ignore any possible steps to slow global warming. This low number, however, helps to put things in perspective.
The FAO has also seen the potential for mitigation measures. Reductions could be achieved, ideally by reducing production and consumption, of course, but also by lowering emission intensity of production. Mitigation potential exists based on the wide gap in emission intensities that exists within production systems and agro-ecological regions. The sheep farms in New Zealand are already in the lower spectrum of emissions, and hopefully they will not only continue with those best practices, but even improve them.
Let them fart !
In the meantime, I am inclined to relax a bit and take a cool approach towards the topic. Keeping in mind those 0.15%, I’d like to simply say: let the sheep fart, it doesn’t even smell that bad !