A different way to measure the climate impact of food

EATING A JUICY steak is worse for the environment than frying up some tofu: that much should come as no surprise. Going vegan can dramatically cut the carbon footprint of your diet. But what about the fewer calories, and lower levels of protein, found in most plant-based foods when compared with meat? That makes it hard to compare emissions of meals that are equally nutritious.

To make the relative carbon impact of foods easier to digest, The Economist proposes a banana index (see our interactive chart below). It compares popular foodstuffs on three metrics—weight, calories and protein—indexed to the humble banana, a fruit of middling climate impact and nutritional value.

Indexing greenhouse-gas emissions to a single food gives a sense of how different foodstuffs rank. Unfortunately for carnivores, beef is bad for the environment no matter how you slice it. Producing one kilogram of mince causes as many emissions as 109kg of bananas (call it a “banana score” of 109). Adjust for nutritional value, and beef’s banana score falls to 54 (one calorie of beef mince causes 54 times as much carbon emissions as one calorie of banana). By protein, it scores seven.

Poultry scores 11 bananas by weight and four by calorie. However, as a source of protein, it is more carbon-friendly than bananas: poultry protein emits just three-fifths of the same amount of banana protein. The same applies to salmon. Unsurprisingly, plant-based alternatives to meat do even better: a meat-free burger, for instance, scores just one-fifth of the emissions of bananas per gram of protein. (Other plant-based foods, such as grapes, sugar and coconut milk, contain barely any protein which sends their banana scores soaring.)

Some foods that out-emit bananas on one metric put them to shame on another. The biggest variance between emissions by weight and calories is in olive oil, which has a banana score of six when measured by kilogram, but scores 0.7 when measured by calories. Others include breakfast cereals, cashew nuts and croissants—which all flip from bad scores to good when measuring by calorie.

Our banana index relies on average emissions for a given food. In the real world some producers are more climate-friendly than others, and some foods travel farther to consumers. But in most cases, differences between foods are much greater than these variables within them. For all the emphasis on locally produced food, transportation contributes less than 10% of most foods’ total emissions; for beef it is usually less than 1%. Our banana index also does not capture other environmental impacts, such as land and water use (though here too, beef tends to fare poorly).

Polling in Europe by Ipsos for Yara, a fertiliser firm, suggests that most consumers want to be more climate-friendly—and with food production responsible for perhaps a quarter of global emissions, eating with the climate in mind would make a difference. The survey showed that just 31% of respondents found it easy to make sustainable choices. Three-quarters said they want labels that would explain the climate impact of their food. Studies have found that labels encourage consumers to choose lower-emission options, although they are not in widespread use. In the meantime, our banana index might help.■

Read more of our analysis on food and the environment:
Treating beef like coal would make a big dent in greenhouse-gas emissions
If everyone were vegan, only a quarter of current farmland would be needed
How much would giving up meat help the environment?
Meet the vegans having better sex than you