Expert View: Five years of work - one label on a packet of crisps

We only know two things about carbon labelling. First, everybody thinks it is a good idea and, second, nobody has the faintest idea how to implement such a scheme on a large scale.

It should be simple - a carbon label records the total CO₂ produced by the making and selling of an article. Consumers can compare the labels of competing products, and manufacturers can work to improve their carbon performance, so helping to reduce greenhouse gas emissions.

But calculating the carbon in the simplest product is a ferociously difficult task, as a recent conference at Oxford's Environmental Change Institute, organised for Tesco amply demonstrated. The worst problems are to be found in packaged food products. A chilled meal might have 40 different ingredients, coming from 10 countries and going through scores of different manufacturing and packaging processes.

How can we calculate the carbon cost of an international commodity like a ton of soya beans without knowing the country they are from, let alone the farming methods used? Even for UK-supplied ingredients, the greenhouse gases arising on the farm are notoriously hard to estimate, depending on soil conditions, how much fertiliser is used and the competence of the farmer.

Manufacturers and retailers that promised to implement carbon labelling may already be regretting their haste. With the enthusiasm of a recent convert, Tesco committed in January to label all its grocery lines, which means putting new labels on more than 100,000 products. As the scale of the task has become clearer, Tesco executives must be worrying that this is the one promise their ever-youthful chief executive, Sir Terry Leahy, will not be able to deliver on before his retirement.

So far, carbon labels have been successfully put on a tiny number of groceries. The Carbon Trust has worked with Boots, crisp manufacturer Walkers and beverage maker Innocent Smoothies to calculate the carbon cost of making and selling just five items. The research showed that a small bag of Walkers cheese and onion crisps weighing 34g is responsible for CO₂ output of 75g, just over twice the weight of the product. Almost half of the greenhouse gases arise on the potato farm, substantially more than in the manufacturing process. Transport to the food shops is relatively unimportant.

Perhaps surprisingly, a 250ml Innocent Smoothie has a carbon footprint of almost 300g, four times the figure for a bag of crisps. For comparison, a large fresh apple or a carrot might be about 25g. A bottle of Boots shampoo produces 160g of CO₂ but I suspect this figure is probably dwarfed by the energy cost of heating the water used to wash the customer's hair. Similarly, Marks & Spencer has found that the carbon costs of producing many of its clothing items are tiny compared with the energy used in washing them in the home. Sensibly, M&S's efforts have therefore been directed towards encouraging its customers to use low-temperature washes.

The Carbon Trust has completed five years of work with Walkers on energy efficiency issues along its complete supply chain. Despite its intimate knowledge of the business, so far we have only got a single label across Walkers' portfolio of salty snacks. Crisps are a simple product with just one key ingredient, usually harvested a few miles from the factory. If it takes this much effort just to label one product, we can be sceptical about ever seeing carbon stickers on every item in a supermarket.

Manufacturers and retailers shouldn't waste too much time or money trying to work out their own carbon footprint. It is far better to concentrate first on the waste of energy in factories and shops. Reducing the energy costs of refrigeration - up to two thirds of electricity used in a supermarket - will yield far greater benefits than employing staff to calculate a carbon label.

Chris Goodall's 'How to Live a Low-carbon Life' is published by Earthscan, £14.99 C.goodall@which.net

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