The way to cut your food’s climate emissions 3i6yr

As the world's population rises, the impact of food on the climate is going up. Fuelled by resource-draining practices and our increasing demand for environmentally-damaging meat, what we eat has never mattered more to the planet's health. Food production currently contributes more than one-quarter of all climate change-causing emissions, when you take into all the steps it takes to get food from field to plate. This includes clearing land to make space for agriculture, making and applying fertilisers, rearing animals and processing, packing and transporting the end result to reach us, the consumers. 

Even if you are not currently thinking about changing what you put on your plate, in a few years we might not have much choice. As climate change continues, the amount of food we can produce from each patch of land is forecast to change – in some cooler places it will go up – but on average, globally, it is expected to go down. That means less food for a rising population. At the same time we expect an increasing number of extreme weather events due to climate change, from droughts to flooding and storms, which can devastate or reduce the size of a crop. Most worrying is that these extreme weather events are becoming increasingly connected across large areas, for example the Northern Hemisphere, potentially causing major food shortages. "The main way that most people will experience climate change is through the impact on food: the food they eat, the price they pay for it, and the availability and choice that they have," says Tim Gore, from Oxfam's Grow campaign.

But it is possible to slow these changes through the food we choose to eat. Not all foods are equal when it comes to causing climate change. Research shows that people are generally not aware of how big the differences are, and will underestimate their food's emissions. Consider two different dinner options: an 8oz steak with fries and a microwaved potato with beans. The steak dinner is over 20 times worse for the climate than the beans dinner, even after taking into cooking. 

Explaining this discrepancy between people's estimates of emissions and the true figure is something that I have first-hand experience in. While most of my career has been spent as a physicist at the University of Manchester, more recently I have applied my expertise in data science to our food chains, writing a book on the subject, and speaking to of the public at science exhibitions.

I find people are usually surprised by the size of the difference between steak and beans, until I explain that about 5% of the calories eaten by a cow are burped out again as methane, which is a powerful greenhouse gas. The bravest then ask about the effect of the beans on our own digestive systems – might these contribute to climate change too? But it turns out that even braver researchers have studied human farts and found that eating beans does not increase the amount of methane they contain – that's one less thing to worry about at least.

Are you thinking of eating differently in the future, on the basis of the information you read so far? Perhaps not. Research on obesity shows that having more information alone is not usually sufficient to change the way people eat. However, it does help, because people become more ive of system changes – for example a sugar tax. 

What system changes could we introduce to help reduce the impact of food on climate change? A first step would be transparency. Take that example of air-freighted fruit – I'd like to see an airplane sticker on all the food that came by air. 

There are different ways of calculating climate impacts. But the vast majority of studies use "kg CO2e" (kilograms of carbon dioxide equivalent). That's a way of adding up the contribution from all of the greenhouse gases, including nitrous oxide and methane, which are the most important contributors from food production. 

An 8oz steak produced in Europe causes 10kg CO2e, on average, whereas the total daily diet of an average global citizen causes about 6kg CO2e per day. Eating 8oz of beef every day is way over our budget. But a microwaved potato and beans leaves plenty of room for eating other food during the day, because it contributes less than 0.5kg CO2e.

Labelling can help address the lack of consumer awareness about food climate impacts. Some of this is starting to happen already, with the food brands Quorn and Oatly showing the emissions for each of their products on their packages. But some people might have a sense of deja-vu. In 2009, Walkers Crisps started printing CO2e on their packets, and UK supermarket giant Tescos started doing the same for hundreds of products – then they stopped, because it wasn't giving them a market advantage. People didn't care enough back then. Do they care enough now? And, even if they do, can we leave this as a voluntary system?

You can see how Quorn calculate their carbon labels in the video below.

But technology can help too. Tech company Wasteless offer solutions for food distributors by using dynamic pricing to react to changes in demand, while FoodCloud redirect surplus to those in need. Consumers can also let their neighbourhoods know about food that is no longer needed, and see it go to a good home with apps such as Olio.

There are things we can all do now right in our own lives, as well as raising awareness more broadly. You can find out about how much your food contributes to your own climate impact using BBC Future's Foodprint Calculator. The calculator also shows food substitutions with a lower impact. 

My advice, as a data scientist, would be to start by focusing on the foods you regularly eat, that cause the most climate impact – if you can change these regular things first then its more manageable and the climate benefits will add up through the year. Then start by looking at quantities – if you could halve the amount per serving, then this would already make a big difference. But most people feel better about adding new things, rather than reducing or depriving themselves of regular things. So focus on adding in lots of climate-friendly foods into your diet, such as vegetables and beans or lentils, which come with a load of health benefits too. 

For example, about 90% of the climate impact of a spaghetti bolognese comes from the beef, with one portion causing about 6kg CO2e. Bulking out the recipe with a couple of tins of lentils will automatically reduce the amount of beef you're eating per portion. If you want to go the whole way, replacing the beef by tinned lentils completely would bring the total climate impact down below 1kg CO2e – one-sixth of the average daily output. 

Has that given you food for thought over your next meal?

*Sarah Bridle is a professor in the physics department at the University of Manchester, UK. She uses data science to study cosmology and food production, and is the author of Food and Climate Change – Without the Hot Air.