Carbon Footprint Labels Are Expensive

Not on the label
May 17, 2007 -- The Economist (Subscription)

Why adding “carbon footprint” labels to foods and other products is tricky

Would you like a footprint on your food? Labels already show fat, salt and sugar content, among other things. But now several British food companies and retailers plan to add “carbon footprint” labels showing the quantity (in grams) of carbon-dioxide emissions associated with making and transporting foods and other goods. The first such labels appeared on packets of Walkers crisps in April. Boots, a British pharmacy chain, will add carbon labels to some of its own-brand shampoos in July. These labels were produced in conjunction with the Carbon Trust, an environmental consultancy funded by the British government, as part of a trial scheme. Tesco, Britain's biggest retailer, has also announced plans to apply carbon labels across its product range and many other firms plan to do the same.

If the idea can be made to work, carbon labels will allow shoppers to choose the products with the smallest carbon footprints and make it possible for them to compare locally produced and imported foods, as well as conventionally farmed and organic products. Claims that some kinds of food are more energy-efficient than others and worries about “food miles” would give way to “a much more rounded, inclusive picture,” says Euan Murray of the Carbon Trust.

But calculating the carbon footprint of a product is far from easy. Unlike the fat or sugar content, it cannot be measured directly. For a start, how far back up the supply chain do you go? Academic “life-cycle analyses” go into painstaking detail, factoring in the emissions associated with building factories in which food is produced, for example. But doing this for thousands of products would be a mammoth undertaking. The trick, says Mr Murray, is to find the right trade-off between rigour and a methodology that works across thousands of items. The Carbon Trust's approach is to include carbon dioxide produced in the manufacturing but not, say, that from employees commuting to work.

How far down the supply chain do you go? The Carbon Trust's labels aim to show the carbon emissions associated with making something, packaging it, getting it to the store and disposing of it. Because bags of crisps delivered to far-flung shops will have travelled farther from the factory, the auditors use an average figure for transport emissions. Similarly, national averages feed into calculations of whether a product or its packaging are recycled, incinerated or put into landfill.

The labels do not count the energy needed for refrigeration, lighting and heating in shops. Nor do they include the emissions that come from using a product. The carbon footprint of boiled potatoes, for example, is dominated by the emissions associated with cooking them. Whether you put a lid on the pan can make more of a difference than how they were farmed, or whether they were produced locally or not. Similarly, the emissions of shampoo depend on how long you spend in the shower, how hot the water is and the quality of your boiler. Such things cannot be captured in a carbon label, so they are not included, says Mr Murray.

A particularly difficult area is agricultural modelling. Some sources of farm emissions, such as the electricity consumption of a milking shed, can be measured directly. Others, such as nitrous-oxide emissions from soils and methane emissions from animals, cannot. For the latter, mathematical models are used instead, says Adrian Williams, an agri-environmental scientist at Cranfield University in England. Such models contain assumptions that not everyone may agree with, however. A recent report funded by DEFRA, Britain's environment agency, found that some organic foods had larger carbon footprints than conventional ones. It was criticised by the Soil Association, Britain's main organic lobby, which took issue with the models used for the calculations.

To complicate matters further, nitrous-oxide and methane emissions from farms far outweigh carbon-dioxide emissions in global-warming potential. Methane and nitrous oxide are taken into account by converting them into “carbon-dioxide equivalent” emissions using conversion factors provided by the Intergovernmental Panel on Climate Change. But the quantification of nitrous-oxide emissions is still not well understood, says Dr Williams, so it is not clear which model to use.

Getting agreement on how best to calculate carbon footprints depends on debate between scientists, retailers, farmers, lobbyists and others. The Carbon Trust has begun a year-long consultation and this month a meeting took place at the Environmental Change Institute at Oxford University, which is looking into carbon labelling for Tesco. Agreement is vital because the labels will be useful only if there is a common standard. Otherwise consumers will not be able to compare apples with apples, as it were.