Photo by Stuart Chalmers. Used under Creative Commons License

In a new piece at Slate, Mark Hertsgaard puts forward the appetizing proposition that the road to a healthier planet is paved with pastured meat. The basis for the article is an interview with Michael Pollan, the best-selling author of The Omnivore’s Dilemma, In Defense of Food, Food Rules, and most recently Cooked. Pollan argues for an agriculture based on “bio-mimicry,” that is, systems which imitate nature. According to Pollan, well-managed grazing can increase the amount of carbon a pasture stores underground. He argues that pastured meat can therefore help to reverse climate change, in addition to improving soil quality and food security. This might surprise people who are used to thinking about the environmental impact of food. Conventional wisdom holds that raising animals for food is highly inefficient and that meat production is consequently very environmentally damaging.

This isn’t the first time Michael Pollan has promoted the idea that meat production can help control global warming. A reader of The Omnivore’s Dilemma might recall similar themes from Pollan’s glowing portrayal of Joel Salatin’s Polyface Farm. In that book, Pollan explains that at Polyface, “a half dozen different animal species are raised together in an intensive rotation dance on the theme of symbiosis.” By placing grass at the foundation of the food chain and scrupulously recycling nutrients, Salatin manages to not only escape virtually all of the negatives of agriculture, from nitrogen pollution to carbon emissions, but also remove thousands of pounds of carbon from the atmosphere. The result, as Pollan puts it, is “utterly convincing proof that in a world where grass can eat sunlight and food animals can eat grass, there is indeed a free lunch.”

That, at least, is how things look through Pollan’s rose-colored glasses. As I mentioned a few months ago, Pollan’s discussion of the ecology of Polyface Farm downplays the importance of feed grain to the farm’s functioning. Pollan notes the role of chicken manure in providing nitrogen¹ for the Polyface pasture, but he fails to acknowledge that much of the nitrogen in chicken feces actually comes from that feed grain². Moreover, some of the carbon stored on Salatin’s pasture also comes from that feed grain. This is important because grain production results in carbon emissions, in large part due to fertilizer application, plowing fields, and fossil fuels burned on the farm.

In January of 2011, Joel Salatin spoke at an event at UC Berkeley, and I had the chance to ask him about feed grain and its implications for the farm’s environmental footprint. My question (video) was,

You talked about the role of animals in sequestering carbon and also in rebuilding the soil, and something that’s missing from that is that the grain that you feed to the chickens also is also essential to that, and it’s not an insubstantial amount, I don’t think, so are you getting more out than you’re putting in in grain, and if not, why is your farm sustainable agriculture and not just outsourcing the environmental degradation to the grain farm?

Salatin’s answer took me by surprise. He said,

That’s a great question, and you are exactly right. In my perfect world, we would eat very little poultry. The omnivore consumption would drop way, way down and the herbivore consumption, which is on perennials would go way, way up, in my perfect world. Actually, everyone else calls us a sustainable farm. I don’t call us a sustainable farm, because at the end of the day I really don’t think we should be raising the number of broilers that we raise, for that very, very reason.

He went on to suggest that he could use a system developed by the Australian farmer Colin Seis, which does not require feed inputs but would only allow him to raise poultry once every five years.

While I can’t claim to be an impartial observer, I found the exchange remarkable. Salatin has acquired rockstar status in the sustainable food movement thanks to Pollan’s account of his use of bio-mimicry in farming. Pollan has emphasized the interconnectedness of the various animal species on the farm. Pollan has quoted Salatin as saying that “everything’s connected to everything else, so you can’t change one thing without changing ten other things” and that Polyface uses “exactly the model God used in building nature.” Yet when asked about his reliance on feed grain, Salatin acknowledged that to make his farm sustainable, he’d have to significantly cut poultry production. (Does this mean that God chose the wrong model in building nature?)

I don’t mean to say that the Polyface model shouldn’t be used, but to call into question the way that Pollan has presented it. To Pollan, Polyface serves as “proof that people can sometimes do more for the health of a place by cultivating it rather than by leaving it alone.” That sounds great, but as Simon Fairlie, puts it in his book Meat: A Benign Extravagance, “However productive Polyface may be, it is in a sense only half a farm, and it doesn’t help to analyse the carbon sequestration on one half, without knowing what is happening on the other.” A reality-based discussion of the environmental impact of Polyface Farm would have to account for any carbon emissions associated with growing the feed grain. It is hard to take Pollan seriously on this issue when he has gotten it so demonstrably wrong in the past and has never offered a correction.

Hertsgaard downplays the need for a more rigorous analysis, pointing out that pasture-based carbon sequestration is based on photosynthesis and that “we are sure photosynthesis works.” But one need not be a photosynthesis denier to question whether Pollan’s model of carbon sequestration is realistic. While photosynthesis is certainly a part of that model, there are other parts which are not nearly as well-established.

For instance, Pollan described an important facet of the carbon farming mechanism to Hertsgaard: >When you have a grassland, the plants living there convert the sun’s energy into leaf and root in roughly equal amounts. >When the ruminant [e.g., a cow] comes along and grazes that grassland, it trims the height of the grass from, say, 3 feet tall to 3 inches tall. >The plant responds to this change by seeking a new equilibrium: it kills off an amount of root mass equal to the amount of leaf and stem lost to grazing. The [discarded] root mass is then set upon by the nematodes, earthworms and other underground organisms, and they turn the carbon in the roots into soil.

Pollan offers no documentation for this claim, which is supposed to explain how grazing animals can increase the amount of carbon stored by a pasture. Nor does he offer a citation for a very similar claim in The Omnivore’s Dilemma. Simon Fairlie, in a sympathetic but honest chapter on carbon farming, notes that of five prominent advocates for the practice (including both Pollan and Allan Savory) none offered documentation for the claim that plants kill off roots when their leaves are trimmed. Fairlie reports having eventually found a research paper³ which cited evidence that grazing resulted in root mortality and speculated that this “could result in significant increases in Soil Organic Carbon (SOC) over a relatively short time.” However, he also notes a more recent paper which confirmed that grazing led to root death but found that this actually decreased soil carbon levels. For my part, I found a 2010 literature review compiled results of studies that compared soil organic carbon levels in grazed and ungrazed plots. The authors identified 12 trials showing an increase in soil organic carbon in grazed plots, 12 trials showing a decrease in soil organic carbon in grazed plots, and 12 more with the grazed and ungrazed plots having equal levels of soil organic carbon.

It’s not entirely implausible that there could be circumstances under which grazing might promote carbon sequestration on a pasture. However, it is overly simplistic to say, as Pollan does, that “If you’re eating grassland meat, your carbon footprint is light and possibly even negative.” The bottom line is that claims about environmental benefits of meat consumption need to be based on evidence. If Michael Pollan has that evidence, I hope he’ll come forward with it. Unfortunately, all I’ve seen from him so far is magical thinking and feel-good talk of bio-mimicry.

Related posts

• Cows against climate change: The dodgy science behind the TED talk (My take on the TED talk of Allan Savory)
• An unlikely fix: Nitrogen fertilizer and organic agriculture (This post focuses on a fundamental difference between agriculture and nature)

---

1. Notably, Pollan claims that Polyface is “completely self-sufficient in nitrogen,” apparently unaware that the feed grain contains nitrogen.↩

2. The chickens do get a small share of their diet from the pasture, but nitrogen which chickens get from the pasture is a distraction. It doesn’t add to the pasture’s supply of nitrogen, because that supply was reduced when the chickens ate from the pasture.↩

3. The article is “The dynamics of soil carbon in rangelands” by G.E. Shuman, J.E. Herrick, and H.H. Janzen, which is chapter 11 in the 2001 book The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect, edited by R.F. Follett, J.M. Kimble, and R. Lal and published by CRC Press.↩