What's the carbon footprint of a potato?

With increased concern about food miles and our carbon footprint, its intriguiug to learn that local firm Walkers Crisps has become the first firm to put carbon footprint figures on its products, with nine more companies set to follow. In April, Walkers Crisps began labelling its cheese and onion bags with a carbon footprint - how many grams of greenhouse gases were emitted in its production - and that has been rolled out to other flavours. The calculations are done by the Carbon Trust, which spent several months working out that 75g of greenhouse gases are given off in the production of a 33.5g bag of Walkers crisps, taking into account the energy used in farming, manufacture, packaging, distribution and disposal.