Plant-based diets and the planet

What difference would a plant based diet make to our climate change gas emissions?
29 September 2020

Interview with 

Sarah Bridle, University of Manchester


A picture of the Earth from the ISS space station


It’s not just our own health that can be improved by a shift towards a more plant-based diet, the planet benefits too. Chris Smith spoke to University of Manchester physicist Sarah Bridle, who’s also the author of the book “Food and Climate Change, without the hot air”, about how that shift might help the Earth...

Sarah - Well, in terms of all the cutting down forests, you have to do agriculture on the land and then animals and fertiliser on the fields and so on, and all the packaging and transport and everything, adds up to about a quarter of all greenhouse gas emissions currently coming from food. And that's increasing as there are more people eating more climate unfriendly foods.

Chris - And what fraction of that quarter is meat?

Sarah - It's about a half of that is coming from meat, depending on how you add it up. But yeah, it's half or more.

Chris - And why is meat so high? Because you think well, meet meat, we're going to eat that. So why would meat contribute so many climate change gases?

Sarah - Well, fundamentally we have to grow a lot of food to feed animals. So it takes about 16 times as much land to produce animal-based foods as it does to produce plant based foods.

Chris - Oh goodness. So in other words, what fraction, if you do the sums then, of the total land in agricultural use is just growing food for animals?

Sarah - About 80%. So about four fifths of the current agricultural land is currently being used to produce food for animals.

Chris - That's a lot, isn't it? So that means then if we all went vegetarian, and I'm not for a minute suggesting that anyone would embrace the idea but if we did, does that mean then that 80% of land would immediately be liberated because we wouldn't have to grow food for animals that we wouldn't want to eat?

Sarah - Very nearly yeah. I mean, we'd have to grow a little bit more plants just to make up for the calories and nutrition we'd lose from the meat. But even then three quarters, 75% of the agricultural land would then be freed up and we could use it for other things like maybe forest, for example, for pulling carbon dioxide out of the atmosphere. And that itself would also help to combat climate change.

Chris - You pointed at this when we first began to talk just now when you said, well, actually the human population, although it's only a quarter of our contributions, the human population is growing. So that quarter is growing as well isn't it? So it's continuing as the human population grows to get bigger and bigger and bigger as a contributor. So even if we did all go vegetarian, we'd still end up with food production being a very significant source of climate change gases.

Sarah - Absolutely. I mean, we have to do something about that three quarters, the rest of it. But if we were to stop burning fossil fuels, then food would then be the biggest contribution to climate change. And certainly, hopefully, we can reduce fossil fuel usage and it will be more and more important in terms of climate change in the next decade hopefully.

Chris - And what therefore is our best approach. How do we get a handle on that 25%, is the food industry. To bear down on that? And also if we do switch away from meat towards more plant based diets, how do we keep driving down the contribution to climate change gases from agriculture?

Sarah - Well, I really, really feel that there's not enough information that's easily accessible at the moment. So quite often people will just say, you know, for example, an average vegan diet causes about half the greenhouse gas emissions of an average omnivore diet. We can do these very, very broad generalisations, but actually in detail, of course, some farmers are working extremely hard to reduce the climate impacts of what they're producing. And so actually what I really want to see is labelling of greenhouse gas emissions on all food packets. And then we could actually go in there and reward the great work that's already being done by many food producers, but also that would mean that food producers themselves will be a lot more aware of their climate impacts and would work on that side as well to reduce the climate impacts of what's being produced.

Chris - Are all meats equivalently evil, or are some worse than others?

Sarah - In terms of climate impacts, there's a big difference between different types of meat. So if we look at something like beef and lamb, then they come from ruminants, they've got a particular type of stomach and about 5% of the calories eaten by a cow are burped out. Burps, very important that, not farted out, as methane. And so that's a very potent greenhouse gas. And so there tend to be over 40 times the amount of climate impacts. So if you get 40 times as much greenhouse gas emissions from eating a piece of beef than the weight of that beef, it's relatively high compared to something like say chicken, which is closer to 10 times. So there's about a factor of four difference between something like chicken and something like beef if not more.

Chris - How does dairy fit into the equation then, because obviously you've got to keep a cow to have milk. And therefore another staple of often many vegetarian diets is cheese, for example, which comes from milk. So how do the equations break down and shake down for the dairy industry?

Sarah - Yeah, so that's absolutely true. And in fact, if you, if you were to look at something like cheese, then it actually on average causes more greenhouse gas emissions than chicken. So if you were a meat-eater who ate only chicken and you replaced all of that chicken with cheese, it would actually be on average worse for the climate.

Chris - Hence you're saying, that's why we need the labelling.

Sarah - Absolutely. And it's just not so well known that there's these big differences.

Chris - And it's simple to say, well, I'll just start eating lots of fruits and vegetables, but a lot of that stuff doesn't grow in this country. So when one factors in the carbon footprint of transport, how does that affect things? And would that be reflected in the label on the supermarket shelf? I would say that will be difficult, wouldn't it? Because how would the supermarket know that I'm going to drive to the supermarket to buy that apple or something and therefore add my carbon footprint to it, or would we just have to live with the fact that extra carbon costs are all necessary?

Sarah - There's lots of different ways of doing the climate labelling. For example, often people don't count the consumer, you know what we do as citizens, within that number. So you might not necessarily have your car journey to the supermarket, but inside that label should definitely be all the transport that's happened to get that food to the supermarket. It very much depends on how that food has been transported. If the same piece of food were to come by ship versus by air, then flying it by air causes a hundred times more climate impact than sending it by boat. So as consumers, we don't usually know when we go to the supermarket, which things have come by air or by boat. And so it's really difficult to know, but if you have something that's come by air then it starts to get climate impacts comparable to those of some of the lower, lower impact meats and animal products.


Add a comment