Here is an article about British supermarket chain Tesco starting a project on labelling the carbon footprint of milk products.
This is quite an interesting development, as it would allow consumers to make their purchase decision based on the environmental impact of what they buy. It also would make retailers and producers more aware of their own business decision, be it for sourcing products or choosing their markets.
Of course, an other very important next step will have to be consumer education about carbon footprint numbers and how to read them, but this learning process was also necessary with nutritional information.
I see this as a very good initiative to identify and segregate sensible products from the not so sensible ones. Very likely, we will see more labelling about environmental information in the future, and not just for food products, but all consumer products.