People will have to be rationed to four modest portions of meat and one litre of milk a week if the world is to avoid run-away climate change, a major new report warns.
The report, by the Food Climate Research Network, based at the University of Surrey, also says total food consumption should be reduced, especially "low nutritional value" treats such as alcohol, sweets and chocolates.
It urges people to return to habits their mothers or grandmothers would have been familiar with: buying locally in-season products, cooking in bulk and in pots with lids or pressure cookers, avoiding waste and walking to the shops - alongside more modern tips such as using the microwave and internet shopping.
The report goes much further than any previous advice after mounting concern about the impact of the livestock industry on greenhouse gases and rising food prices. It follows a four-year study of the impact of food on climate change and is thought to be the most thorough study of its kind.
Tara Garnett, the report's author, warned that campaigns encouraging people to change their habits voluntarily were doomed to fail and urged the government to use caps on greenhouse gas emissions and carbon pricing to ensure changes were made. "Food is important to us in a great many cultural and symbolic ways, and our food choices are affected by cost, time, habit and other influences," the report says. "Study upon study has shown that awareness-raising campaigns alone are unlikely to work, particularly when it comes to more difficult changes."
The report's findings are in line with an investigation by the October edition of the Ecologist magazine, which found that arguments for people to go vegetarian or vegan to stop climate change and reduce pressure on rising food prices were exaggerated and would damage the developing world in particular, where many people depend on animals for essential food, other products such as leather and wool, and for manure and help in tilling fields to grow other crops.
Instead, it recommended cutting meat consumption by at least half and making sure animals were fed as much as possible on grass and food waste which could not be eaten by humans.
"The notion that cows and sheep are four-legged weapons of mass destruction has become something of a distraction from the real issues in both climate change and food production," said Pat Thomas, the Ecologist's editor.
The head of the United Nations intergovernmental panel on climate change, Rajendra Pachauri, also sparked global debate this month when he urged people to have at least one meat-free day a week.
The Food Climate Research Network found that measured by production, the UK food sector produces greenhouse gases equivalent to 33m tonnes of carbon. Measured by consumption - including imports - the total rises to 43.3m tonnes. Both figures work out at under one fifth of UK emissions, but they exclude the indirect impacts of actions such as clearing rainforest for cattle and crops, which other studies estimate would add up to 5% to 20% of global emissions.
The report found the meat and dairy sectors together accounted for just over half of those emissions; potatoes, fruit and vegetables for 15%; drinks and other products with sugar for another 15%; and bread, pastry and flour for 13%.
It also revealed which parts of the food chain were the most polluting. Although packaging has had a lot of media and political attention, it only ranked fifth in importance behind agriculture - especially the methane produced by livestock burping - manufacturing, transport, and cooking and refrigeration at home.
The report calls for meat and dairy consumption to be cut in developed countries so that global production remains stable as the population grows to an estimated 9bn by 2050.
At the same time emissions from farms, transport, manufacturing and retail could be cut, with improvements including more efficient use of fertilisers, feed and energy, changed diets for livestock, and more renewable fuels - leading to a total reduction in emissions from the sector of 50% to 67%, it says.
The UN and other bodies recommend that developed countries should reduce total emissions by 80% by 2050.
However, the National Farmers' Union warned that its own study, with other industry players, published last year, found net emissions from agriculture could only be cut by up to 50% if the carbon savings from building renewable energy sources on farms were taken into account.
The NFU also called for government incentives to help farmers make the changes. "Farmers aren't going to do this out of the goodness of their hearts, because farmers don't have that luxury; many of our members are very hard pressed at the moment," said Jonathan Scurlock, the NFU's chief adviser on renewable energy and climate change.
Different diets
The way we eat now (average person in the UK, per week)
1.6kg meat and 4.2 litres of milk, which is equivalent to:
6 sausages (450g)
2 chicken breasts (350g)
4 ham sandwiches (100g)
8 slices of bacon (250g)
3 burgers (450g)
3 litres of milk
100g of cheese and a helping of cream
Future recommended diet (average person, per week)
500g of meat and 1 litre of milk, which is equivalent to:
1 quarter-pound beefburger
2 sausages
3 rashers of bacon
1 chicken breast
1 litre of milk or 100g of cheese
