Litre of Milk

0.40kg

1 liter of milk

I have been in touch with Jamais Cascio <cascio@openthefuture.com> in America.
I read his article The Cheeseburger Footprint (http://www.openfuture.com) and it was so good
I asked him if he could calculate the footprint of a litre of milk.
Here is his very thorough answer. Check it out!

In order to fully calculate the carbon footprint of milk,
I'd need to have numbers on energy consumed in processing the milk
(pasteurization, bottling, etc.) and transportation;
beyond that, the main carbon impact will be from the methane produced by the cattle.
This calculation would 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)

...or...

(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

but!

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.

Sources:
* 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