Tesco is trialling telling customers about the greenhouse gases emitted from "seed to store" of some products, as it hunts the green pound of customers worried about climate change.
From Tuesday, the world's third-biggest food retailer is piloting carbon labelling across 20 products, putting a number on the packet showing greenhouse gas emissions per helping of certain items including potatoes, orange juice, washing-up liquid and light bulbs.
The government-funded Carbon Trust and the Environment Ministry are backing the initiative which aims to add the power of consumer spending to fraught political efforts to curb greenhouse gas emissions.
But Tesco won't put a timetable on rolling out the initiative further across its product range of tens of thousands of goods, partly because of the complexity of measuring emissions.
"Let's see what the response to this is and in the meantime we'll measure the emissions of more products," said David North, Tesco's community and government director.
"This is a pilot, it has to be a pilot because we have to be sure it works. There isn't consensus about every piece of data and you wouldn't expect there to be."
Increasing concern about climate change has put pressure on companies to measure the lifecycle carbon emissions of their products, called carbon footprinting, a complicated calculation which can include how a farmer tills his soil.
For example researchers are still trying to pin down exactly what the greenhouse gas emissions are from biofuels, which use agricultural crops to substitute for gasoline as a transport fuel, and which Tesco uses across its lorry fleet in Britain.
"We need to get increasingly better, more granular data. Better research is coming out all the time," said Euan Murray, head of carbon footprinting at the Carbon Trust.
"But we've absolutely got what we need (for this pilot)," he added, saying that the Carbon Trust was measuring emissions using both its own commissioned and published academic research.
None of the 20 Tesco trial products were air-freighted, said Murray. Measuring the contribution of aviation to global warming has proved especially complicated.
Pepsico last year in Britain rolled out carbon labelling on some potato chips, or crisps, also under the Carbon Trading initiative.
The project had the backing of big retailers, the food and drink industry and of Britain's National Farmers' Union, as it tries to create a common standard with public buy-in, said Murray, who added more labelled products would be announced through the year.
