THE CARBON COST OF FOOD
It is surprisingly difficult to work out the carbon footprint associated with our diets: it depends as much on where and how the food we buy was grown as what we actually eat. For instance, some beef comes from calves raised within dairy herds, while other beef comes from calves raised in non-dairy herds. Researchers argue the ‘dairy beef’ carries a significantly lower carbon footprint because the herd is effectively growing two products – milk and beef – lowering the carbon footprint of both. The following is a very rough guide of the carbon cost of food, using the same data that Dr Graham Horgan at Biomathematics and Statistics Scotland and his colleagues are using in their algorithm.
fraction goes into building the muscle and other tissue we consume as meat, making the process of ‘growing’ meat extremely inefficient – although Scarborough says the problem isn’t as bad for small animals like chickens. “You don’t have to feed a chicken anywhere near as much [as you must feed a cow] to get a kilogram of meat,” he says.
Even so, all meat carries a relatively high carbon cost. Perhaps in recognition of this fact there has been an upsurge in the number of vegans in the UK. According to some estimates, there are 600,000 British vegans today – four times as many as in 2014. But vegans in the UK are still outnumbered roughly 100 to 1 by non-vegans. Even if people are convinced of the environmental benefits of going vegan, they may be reluctant to make that shift. They might even balk at the idea of replacing lamb or beef with low-carbon alternatives: swapping a beef burger for a locust burger, for instance, or trying what might be the next food trend: lab-grown meat.
Prof Ermias Kebreab, a biologist and ecologist at the University of California, Davis, thinks that there might be a way to sidestep this reluctance. If we are unwilling to change our own diets, then perhaps the solution is to change the diets of the animals many of us eat instead.
Last year, he and his team demonstrated that by supplementing animal feed with about 1 per cent by weight of a particular strain of seaweed, they could half the amount of methane that cows belch into the atmosphere – known as ‘enteric methane’. This is because the seaweed reduces the ability of microbes in the cow’s stomach to generate the methane: the animals burp out larger quantities of hydrogen gas instead, which has an indirect, smaller impact on global warming. “Most of the emissions [associated with cattle] are from enteric methane,” Kebreab says. “So, if you are able to reduce the emissions by 50 per cent – that’s absolutely huge.”
Encouraging though this is, it doesn’t reduce the carbon footprint of beef and lamb to the level of beans or pulses, says Scarborough. Supplementing livestock diet with seaweed can’t change the fact that most of that animal feed consists of grain we could eat ourselves. Some consumers might protest that the beef on their plate comes from ‘pasture-raised’ cows that ate grass rather than grain – but Scarborough says many of these animals are actually brought into cow sheds at night and given grain.
HAVE YOUR STEAK AND EAT IT TOO
At this point, one might be forgiven for concluding that
“THE PROBLEM IS THAT THE NUMBER OF ANIMALS IN THE FOOD SYSTEM RIGHT NOW IS OVERWHELMING IT”
Scarborough and researchers like him will only be satisfied when all of us have adopted a vegan diet. He stresses that this is far from being true. In fact, he says, some scientific models suggest it is slightly more efficient to have small numbers of livestock in the agricultural system than none. For instance, in manageable quantities, animal manure is a useful fertiliser. “The problem is that the number of animals in the food system right now is overwhelming it,” he says.
It’s not about giving up meat, says Scarborough, but eating far less of it. Doing so is good for animal welfare too. If we eat less meat, we can ‘afford’ – from an environmental perspective – to allow farm animals to live a free-range life rather than raise them through intensive farming. In other words, British consumers should be able to adopt a diet with good environmental and ethical credentials – if they are willing to eat no more than about one portion of meat per week.
Dr Graham Horgan and his colleagues at Biomathematics and Statistics Scotland designed an algorithm (muncher.aws.bioss. ac.uk) that aims to nudge people towards making those kinds of dietary changes. It assesses someone’s food shopping list and, using data on the range of carbon footprints associated with each product, suggests relatively small tweaks that should reduce the carbon cost while still meeting nutritional requirements. For instance, the first thing the algorithm does is increase or reduce the quantity of any given item on the list by up to 50 per cent. Then it considers adding small quantities of foods not on the shopping list – a tin of mackerel, for instance – that can provide key nutritional requirements at a relatively low carbon cost. “Our approach was to try to avoid saying ‘cut out red meat altogether’ and simply say ‘eat less red meat’,” says Horgan. “I feel that might be more acceptable to consumers.”
Just by making these changes, about 50 per cent of people in a 2016 study published by Horgan and his colleagues could continue to eat meat but also reduce the carbon footprint of their diet to a level where it released only 3.1kg CO2e per day. This isn’t too much higher than the 2.9kg CO2e per day for a vegan diet that Scarborough calculated. Horgan now wants to test whether the algorithm can have a real-world impact on the dietary choices made by average British consumers.
Beyond cutting down on meat there is at least one more thing consumers can do to lower their dietary carbon footprint: learn