Waste milk creates a carbon footprint equivalent to thousands of car exhausts, according to a study that highlights the environmental costs of inefficient farming and the aggressive marketing of supermarket food.
Scientists have calculated that the 360,000 tonnes of waste milk that is poured down British drains each year creates greenhouse gases equivalent to 100,000 tonnes of carbon dioxide, which is about the same as that emitted in a year by 20,000 cars.
Figures show that 99 per cent of milk that is thrown away by British consumers is designated as "avoidable waste". Almost half of this waste is a result of too much being served, with the rest discarded for being sour or past its sell-by date.
The scientists also found that if the developed world cut its poultry consumption to Japanese levels – about half of those in the West – the cut in global greenhouse gas emissions would be equivalent to taking about 10 million cars off the road permanently.
The researchers concluded that reducing food waste and cutting back on meat and dairy produce in favour of vegetables could have a significant impact on the greenhouse gases linked with climate change, specifically nitrous oxide which is about 300 times more potent than carbon dioxide and is rising globally as a result of agricultural expansion.
Dr David Reay at Edinburgh University, who led the study on nitrous oxide published in the journal Nature Climate Change, said: "Nitrous oxide is the major greenhouse gas from agriculture. It stands out as the gas you can really reduce in terms of emissions if you can cut down on agricultural waste and increase agricultural efficiency. Eating less meat and wasting less food can play a big part in helping to keep a lid on greenhouse gas emissions as the world's population increases."
Concentrations of nitrous oxide in the atmosphere have risen significantly since 1990 and are expected to increase even more rapidly by 2030 as a result of agricultural expansion and the widespread use of nitrogen fertilisers. Growing cereals for animal feedstock and biofuels would boost nitrous oxide levels still further, the researchers said.
"Population growth means that more food has to be produced and so this source of greenhouse gas emissions will continue to grow if everything else stays as it is," Dr Reay said.
"At present about 30 per cent of food is wasted globally. If we can tackle this, it would be like taking about 20 million cars off the road permanently."