One of the main motivations behind becoming vegan (or at least vegan-ish) was learning that cow flatulence is one of the main contributors, bigger than car exhaust even, to global warming. I came to this belief long before I had the ability, or the education necessary, to adequately assess the science. Now that my veganism is grounded in more ethical concerns, I have decided to reflect on some of my initial reasons to see if they conform to the science. This is not a ‘debunking’ post, since there does seem to be evidence on this issue, but the answer isn’t at all clear, and unpacking it can be a lesson in the complicated inter-connectivity of the human impact upon Earth’s climate.
Cow Burps: The Introduction of Methane into our Atmosphere
If I can debunk one thing, it isn’t cow farts, but their burps, which contribute the largest impact on the climate. Cows, which belong to the class of animals called ruminants, produce a large quantity of methane from bacteria which help to aid in digestion. I won’t cover exactly how methanogenesis works, but it is fascinating, and you could learn more about it here. What interests me is how this gas, once it is expelled, impacts the climate.
The first thing to note, which is integral to this issue, is that methane, in fact, is increasing in our atmosphere. From about 700 ppb pre-industrialization to about 1800 ppb today (2011), the highest concentration in 800, 000 years. However, there are several contributing anthropogenic factors, such as rice agriculture, landfills, natural gas, ecological conversion of forests into agricultural plots, the release of methane from glaciers and permafrost due to warming effects already anthropogenically caused, and of course, cow burps.
It is hard to put a number on how much of this atmospheric methane is directly caused by cows, this is due to the variability in the sources of methane release. Some estimates put cattle methane production at about 37% of all anthropogenic sources of methane in the atmosphere. Since cows can produce between 30-50 gallons of methane per day, depending on their diet, this number is difficult to quantify when assessing cattle’s long term impact on the climate.
Is Methane Worse than Carbon Dioxide?
Almost everything you read online tells you that methane is about 20-30 times worse as a green house gas compared to carbon dioxide. This figure is measured by GWP (global warming potential), which is a relative measure of the amount of heat trapped by a green house gas, compared to a similar weight of carbon dioxide. This can get complicated, given that methane has a shorter half life than carbon dioxide when it is in our atmosphere. In a 20 year window, methane can be 86 times worse, as a green house gas, compared to carbon. The 20-30 times figure is the difference in effect, compared to carbon dioxide over a 100 year period. The longer window you look at, the more methane’s GWP will decrease.
When compared to car exhaust, cow burps are worse in the immediate future, but not as bad as car exhaust in the long term. The take home message is that both are bad, but the relative risk between the two is not as simple to calculate.
One solution is to modify the cows diet in order to decrease the amount of methane produced. Switching to crushed oilseeds reduced methane production in cattle by about 20%. Feed supplements have also been designed to reduce methane gas production in cows. Cows given a methane inhibitor decreased methane production by 30%. However, all of these are added costs into a system that would still add inputs into the climate system which impact warming.
In the end, I still think veganism, or at least a non-dairy, non-beef, diet is one of the best strategies towards reducing this greenhouse gas. This, of course, will not offset our climate impact completely. Any type of agriculture is going to have a release of greenhouse gases.So going off dairy and beef means calories created by other means, albeit with a substantially smaller impact.
Realistically, going completely off beef and dairy won’t be accepted by most people, so even a modest reduction in these products can have some sort of effect. The best solution is probably one that combines all three strategies. Change diet when the cost to do so is cheaper than supplementation. Supplement when changing diet is more expensive. All the while decreasing our consumption of cow related products.
I am not a climate scientist, nor a chemist, nor an agricultural ecologist. So, if any of the information here is inadequate please message me and I will update, fix, reform what I have written here to better suit the data.