Food and Carbon Footprints

Whilst standing in the line the other afternoon at the local Max Burger Restaurant waiting to order some falafel balls, I was drawn to the fact that they had actually gone to the trouble of labelling each menu item with a carbon footprint figure. Far from me to underestimate the intellect of those in the restuarant that day I wondered if any had paid attention to the CO2 numbers and if so did they actually understand what it all meant or indeed if it had influenced what they ended up buying? I must admit the cynic in me thought the whole exercise was an attempt to get one up on the McDonalds and Burger Kings of the world but by a strange coincidence I found this video on the BBC website....it seems Sweden is making a concerted effort to educate/advise consumers as to the impact the production of their food has on the environment. Does anyone know how the CO2 figure for a burger or a box of cereal is actually arrived at? Is there a recognised standard for calculating such things?

http://news.bbc.co.uk/2/hi/programmes/world_news_america/8402877.stm