The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change

Climate Change and Food: Red Meat

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I have talked about climate and food before in terms of how climate change influences the food supply, but what about the other way around? How does our eating influence the climate? As many readers are probably aware, a significant amount of our collective carbon footprint (about one quarter) comes from our food system and meat-based foods have a larger footprint than plant-based foods. But how much difference between foods is there? What is the best way to cut carbon emissions out of one’s personal diet? Does it matter whether the meat is local or free-range?

I didn’t know either. So I’ve done some reading.

The numbers don’t look good for meat

The short answers are that the difference is huge, the best way to cut emissions is to eat less meat, and free-range and local do matter but, as far as the climate goes, not very much. There are some complications and nuances, of course.

I found an article that includes a graphic showing the carbon footprints of various food types (chicken, beef, eggs, lentils, etc.) expressed in kilograms of carbon dioxide equivalent (CO2e) per kilogram of food. “Carbon dioxide equivalent” means all greenhouse gasses taken together and expressed in terms of their impact on climate. So these figures include methane. Logically, the numbers would be exactly the same with any other measure of weight–the point is there is a ratio between amount of food and amount of emissions.

The simplest thing is to read the article, which you should do anyway because it’s fascinating. Here is the link. But I’ll summarize the most striking parts–for simplicity, I’ll give a single numbers for this; instead of writing “5kg of CO2e per kg of food,” I’ll just write “five.”

Lamb is the most carbon-intensive meat by far, at 39.2. Less than five of that is transportation and processing, which presumably means that if you raised your own lamb in your back yard, killed it yourself, and then had a carbon-neutral barbecue, it’s number would still be around 36. The next-closest competitor is beef, at 27, and then the other animal-based foods on the list cluster between 13.5 and 4.8. In contrast, the various plant-based foods on the list all cluster between just under three and just under one. The importance of transportation and processing varies, but only in potatoes is it the majority of the total figure.

I can think of several possible complications (besides grass-fed vs. grain-fed, which I’ll get to later).

  • What if the animal is a by-product of another industry? For example, if a flock of sheep are managed for milk and wool as well as meat, so that only excess ram lambs are slaughtered, then the carbon footprint of the flock is the same as it would be if those excess animals were not eaten (letting them live as pets would actually increase the carbon footprint of the operation, aside from the other ethical questions involved). In such a case, the same kilogram of CO2e has to share meat, milk, and fiber,and the whole operation is much more efficient than it might seem, right?
  • Do the figures for animals include emissions from transporting animal feed?
  • Why is the footprint of cheese six times that of yogurt given that most of them are processed milk?
  • The study focused on food in Britain; are these numbers different in other countries, such as the United States?
  • What is the footprint of highly processed foods, such as candy or fast food?
  • Since different kinds of food have different nutritional profiles, how would this comparison work if the unit of comparison were nutritional value, rather than weight? Nutrition is complex, so it might be impossible to do that kind of study, but the issue could still be important.

I do not have answers to those questions.

In any case, clearly generally similar diets, such as two different versions of mostly-plant-based omnivory, might have extremely different carbon footprints. The study that released these numbers found that while the difference between eating a lot of meat and eating a little is huge, the different between eating a little meat and none is small.

What is so bad about meat?

The clear take-home message here is that giving up beef and lamb (except possibly where these are byproducts of dairy production?), and cutting way back on other animal-based foods, is one of the most powerful steps a person can take to address climate change (aside from voting!). So, why are meats so bad for the environment? We have to be very clear, here; this is not about animal rights, which is an important but separate issue.

I have not seen this issue addressed directly, but the Second Law of Thermodynamics, not to mention public tastes in food, is almost certainly relevant.

The Second Law states, in essence, that every time energy moves or changes form, some of it is lost. This is why, for example, a ten pound house cat needs to eat more than ten pounds of meat in its life. This is also why ecosystems always have more plant-eaters than carnivores and more plants than plant-eaters. Most of what an animal eats does not become meat–what happens to it? Some of it becomes bone or other tissues we don’t want to eat. Some of it is never digested and simply passed as feces–which decomposes into carbon dioxide or methane–or as flatulence, which is also methane. But most of that missing food is exhaled as carbon dioxide.

One way to think about this is that all carbon that is taken up by plants is ultimately either interred in long-term storage as fossil fuels, or released again to the atmosphere when the plant rots or burns or is metabolized and exhaled. Eating food is the exact chemical equivalent of burning fuel. So, when a human eats a pound of plant matter, “burning” that “fuel” results in carbon emissions. But when we eat a pound of meat, that meat represents all the plants that animal ate to grow that meat–and all of that plant-fuel is “burned,” whether in the meat-animal’s body or in the human’s. More plant-fuel burned means more emissions released.

Cattle and sheep are both ruminants, meaning they don’t actually eat food directly. The food they swallow is eaten by bacteria in their guts, which in turn create food for the cattle. So you get another layer of energy transformation and thus another layer of energy dissipation–the bovine gets less energy out of the food and has to eat more, so more plants are “burned” as “fuel” for somebody. And the waste product of these bacteria is methane, which is a very powerful greenhouse gas.

So, meat has a larger carbon footprint than vegetables and ruminants (cattle and sheep) have a larger carbon footprint than other animals (pigs, chickens, turkeys, etc.).

Does grass-fed matter?

Most animals raised for the industrial food supply spend at least part of their lives–and sometimes all of them–in some version of a small cage being fed some kind of grain-based, heavily processed diet. There are all sorts of reasons why this is a terrible, horrible thing and why if you are going to eat meat, you should really choose only free-range animals (please note that “free-range” is a legally slippery term and that finding meat that lives up to the intent of the phrase takes some research). Is the climate another such reason?

The answer to that one depends who you ask.

An animal’s personal freedom has no particular bearing on carbon emissions. What makes the difference is whether it is grazing or browsing, as opposed to being fed corn (as would happen in a cage or cage-like feedlot). Logically, feed carries a larger carbon footprint because it must be transported and processed, whereas pasture is eaten where it grows. In fact, one of the best ways to keep open land from being converted into housing developments is to put cows on top of it. All of that argues for grass-fed meat having either a smaller carbon footprint, or possibly a slightly negative footprint, if pasture sequesters more carbon than cattle release.

On the other hand, cattle, at least, have to live longer to get to slaughter weight if they stay on pasture. More time living means more time farting, which could mean a larger carbon footprint. And while cattle are healthier eating grass, they get more energy from eating grain (which must be why they gain weight faster that way). So a day eating grass presumably means more farts than a day eating grain, too.

Which argument is actually true seems unclear at this time and might depend on the details of the cattle operation in question. And I have not found anything on how free-range living might influence the carbon footprint of other food animal species.

Wait–haven’t there always been cattle?

This question was posed by one of my Facebook friends and it’s a good question. How could cattle be a factor in increased climate change given that cattle themselves are hardly new?

This was my answer:

xkcd land mammals

From XKCD, https://xkcd.com/1338/, used in accordance with the cartoonist’s policy

 

This graphic shows that almost half of the land mammal compliment of the planet, by weight, is cattle. The vast majority is either humans or animals that humans eat. The reason it makes sense to do this comparison by weight rather than by head is that weight is a good proxy for how much animals eat and, thus, how much plant “fuel” they burn and how much CO2e is released. Consider that the energy in a pound of mouse meat is probably similar to the energy in a pound of hamburger–about the same number of calories. There are some potential complications here, but two thousand pounds of mice probably eat very roughly the same amount as two thousand pounds of cow. So, the fact that our planet has a huge number of tons of cattle right now means that a huge amount of plant-fuel is being “burned” by cattle these days.

Now, I am fairly confident that while there have been cattle for millennia, there have not been THIS MANY cattle until very recently.

I also suspect that this massive pile of mooing would not be possible without fossil fuel–and it certainly wouldn’t be economical. Feed could not be cheaply moved in to feed lots and beef (grass-fed or grain-finished) could not be distributed widely enough to meet enough consumers to justify the size of the herd. If this is the case, then excessive cattle farts are simply another symptom of fossil fuel use.

But, even if the huge herd of cattle is new, surely something else was eating all those plants before, and releasing a corresponding amount of waste and flatulence? Like, all the wild animals we’ve squeezed out of existence lately? Maybe and maybe not. Perhaps a lot of those plants used to just not get eaten and to enter into long-term storage on their way to becoming fossil fuel. Or maybe the wildlife released more carbon dioxide and less methane and so had a lower carbon footprint. There are possibilities. Or maybe the farts of cattle are actually irrelevant to climate change and the real carbon footprint of food is only the fossil fuel use and the ecological degradation associated with it?

That one I do not know.

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Author: Caroline Ailanthus

I am a creative science writer. That is, most of my writing is creative rather than technical, but my topic is usually science. I enjoy explaining things and exploring ideas. I have one published novel and another on the way. I have a master's degree in Conservation Biology and I work full-time as a writer.

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