« Technology as Political Catalyst | Main | Footprint Database »

Milk's Hoofprint

I was asked in email if I'd calculated the carbon footprint of milk, along with the footprint of a cheeseburger, and I realized that I had most of the figures I'd need already in hand.

[Caveat: In order to fully calculate the carbon footprint of milk, I'd need to have numbers on energy consumed in growing cattle feed for dairy cows, processing the milk (pasteurization, bottling, etc.) and transporting the results; however, the main carbon impact will be from the methane produced by the cattle, so that's where I'll focus.]

This calculation should be reasonably straightforward -- a first pass estimate would be

(Amount of methane produced by a milk cow in a year) / (Amount of milk produced by a milk cow in a year)


(242 lbs of methane)* / (19,951 lbs of milk)** = 0.012 lbs of methane per lb of milk

1 gallon of milk = ~8.5 lbs, so

1 gallon of milk = 0.102 lbs of methane


1 unit methane = 23 units of CO2 in terms of greenhouse impact, so

1 gallon of milk = 2.35 lbs of CO2 equivalent

Add in a pound of CO2 equivalent for processing and transportation (as a very crude figure), and that ends up to be about 3.35 pounds of CO2 equivalent per gallon of milk. Call it three-and-a-half pounds of CO2 equivalent per gallon of milk.

Or, in metric:

1 liter of milk = 282 grams of CO2 equivalent in methane. With transport & processing, call it about 400 grams of CO2 equivalent per liter of milk.

As with the cheeseburger figures, these are very fuzzy numbers, and the actual amount will vary on the basis of how much carbon is produced farming and transporting cattle feed, collecting and pasteurizing the milk, and trucking the gallons to your local grocery store -- along with how much milk a given cow produces (which can vary considerably).

Repeat after me: everything we do has some level of a carbon footprint. The achievable goal is to make smart choices about what kind of footprint we'll make, and what we'll choose to avoid. The first step in making a smart choice is understanding one's options. So drink milk. Eat a cheeseburger. Heck, drive a big truck. But don't do it without accepting the consequences.

* Methane amount: http://www.epa.gov/rlep/faq.html (in kilos, 1 kilo = 2.2 lbs)
** Milk per cow: http://usda.mannlib.cornell.edu/usda/current/MilkProdDi/MilkProdDi-04-27-2007.txt


1 unit methane = 23 units of CO2 in terms of greenhouse impact

Jamais, where are you referencing the GHG impact based on the specific greenhouse gas?

Footprints are useful tools because we have to know where the big-impact choices are in the system. But I'd echo and expand on your cautionary note about taking them too literally. We are talking about flows and loops, not just cause-effect pairs. Think of water flowing around a (complex) circular river: Start pumping in more over here, and you'll get some flooding over there. The point is not to reduce the flow to zero everywhere we can, but to balance, equalize, and generally make for a smoother flow. This is both harder and easier than it looks.

Kim, the methane comparison is the low end of the various comparisons I've seen. The wikipedia entry has it at 25 for the hundred year impact, based on the latest IPCC. Of course, the 20 year impact is actually 72 times CO2, and since methane cycles out of the atmosphere in 10 years, that may be the more accurate way of measuring.

Hey Jamais. I'm finding your conclusion very complicated. Could you clarify what you mean by "Don't do it without accepting the consequences"? It seems to me that just because a person knows and is willing to accept consequences does not mean we can then say they should act as they like, especially where the consequences to that person maybe be slight compared to the consequences to us and others. Climate change is a social justice issue, and so any member of society should be able to hold prescriptive beliefs.

See you at City Lights, I hope!

Dear Jamais
Two questions:
(1) What about nitrous oxide emissions from the manure cycle?
(2) Isn't there a qualitative diffence between methane/nitrous oxide/deforestation emissions on the one hand and fossil fuel emissons on the other? The first just shuffles around the carbon that is available on the surface of the earth, and is theoretically remediable over 50 or 100 years. The second releases carbon that has been buried and immobilized for millions of years? And the fossil fuel constitutes 75 per cent of all emissions.


Creative Commons License
This weblog is licensed under a Creative Commons License.
Powered By MovableType 4.37