The issue of the livestock-climate connection has catalyzed a debate not only about whether and to what extent we should consume animal protein like meat and dairy, but what kind of system of livestock production is more sustainable from a greenhouse gas perspective if and when we do choose to continue consuming it.
For the carbon conscious consumer pained at the thought of giving up his or her Sunday roast or morning milk for coffee and cereal, what are the alternatives to an animal-free diet?
Sourcing meat, milk and eggs produced by grass-fed livestock have often been touted as an antidote to most of the environmental ills incurred by our mainstream system of feedlot agriculture.
Grass-fed (also known as 'free range' and 'pasture-raised') animal agriculture has even gotten some significant airplay as a method of production that can actually decrease carbon in the atmosphere, thereby reducing (and according to some proponents, reversing) climate change.
This assumption is based on a myriad of reports by agricultural scientists that conclude that grazing livestock on grass can sequester a substantial amount of carbon in the soils. In the past few years, the phenomenon on soil carbon sequestration has received prominent attention by the United State Department of Agriculture (USDA), the U.S. Environmental Protection Agency (EPA), and United Nation's Food and Agricultural Organization (FAO), particularly in its landmark report Livestock's Long Shadow.
Some supporters of grass-based agriculture have taken these findings several steps further in advocating it as a "silver bullet" against global warming. One notable proponent of this theory is Polyface farmer Joel Salatin, who was heavily featured in both Michael Pollan's book Omnivore's Dilemma and this summer's documentary film, Food, Inc.
Salatin uses a form of holistic management where cattle are kept in close packs mimicking bison herds and are intensively grazed on alternate swaths of pasture from several hours to several days before switching to the next one, in a practice commonly referred to as 'rotational grazing.' Regarding questions of climate change and animal agriculture,
If every cattle producer in the United States used his methods of rearing, and poultry and pork production was in turn drastically reduced, "in less than 10 years, we would sequester all the carbon that's been emitted since the beginning of the industrial age," Salatin told Mother Earth News.
A Vermont-based collaborative known as the Carbon Farmers of America promotes a similar theory. It even offers training and consulting to farmers interested in building topsoil on their land and thus increasing carbon stock in their pasture, as well as "sell" carbon sinks to consumers interested in offsetting their emissions.
Co-founder Abe Collins states that he is not an avid fan of offsets, but is looking for proactive "public participation in the carbon cycle." He also clarifies that he still believes we need to scale back considerably from burning fossil fuels in the future in order for soil sequestration to continue being effective means of mitigation.
Pasture-Raised Not a Panacea
The claims of Salatin and the Carbon Farmers of America seem to overlook many of the caveats raised by agro-ecologists about the limits of soil carbon sequestration. For instance, most experts agree that soil sequestration is only a temporary fix. In a best case scenario, newly converted pastureland can be projected to store carbon for a maximum of 50 years before it reaches a saturation point. More average estimates put this time limit at 25 to 30 years.
Pasture also has to be carefully managed and alternated. Otherwise, if done the wrong way, it can lead to overgrazing and desertification. Additionally, many regions and land types in the U.S. and abroad are not suitable for achieving sequestration through grazing. This includes some of the more arid lands in the American West and Midwest.
In fact, not only is there limited suitable pastureland available for maximizing carbon sequestration in the U.S., there may also simply not enough available land surface area to graze all the cattle needed to keep up with our current rate of beef and milk consumption. According to a 1997 report by Cornell University agro-ecologist David Pimentel, if all U.S. cattlemen switched to using only pasture-based production systems, consumption from animal protein derived from cows would have to drop from 75 grams to 29 grams per day.
In response to some of the extravagant claims of proponents of grass-fed livestock production, as well as the growing popularity of the companion local and organic movements, some researchers are releasing papers that criticize the carbon sequestration potential of grazing as overstated.
Not only that, some claim that confined, grain-fed production actually has the lower carbon footprint than its free range counterpart. This includes a report recently presented at the 71st Cornell Nutrition Conference entitled "Demystifying the Environmental Sustainability of Food Production."
Specifically, the report referred to the larger methane emissions that occur due to enteric fermentation in cattle that are fed grass as opposed to grain. Part of this stems from the fact that grass-fed cows simply live a lot longer and so produce more methane over the course of their lifetime. However, it also seems that a grass-based diet also plays a role in inducing more methane release in cows.
Other experts disagree with the overall sentiment of the conference paper.
"I seriously doubt that confinement cattle will ever have a smaller CO2 footprint than grass-fed cattle," remarked Pimentel.
Even though Pimentel agrees that grass-fed cows have higher methane emissions than grain-fed, he notes that most carbon footprint comparisons of the two models of production fail to consider the energy inputs in producing livestock feed (particularly corn), transportation of feed to feedlots, and the exportation and disposal of manure in their estimates.
"If all of these factors are measured, then the feedlot cattle contribute significantly more greenhouse gases," Pimentel says.
Another paper by the USDA's Agricultural Resource Service concluded that in the right region and when practiced properly, grazing farms have significantly lower greenhouse gas impact than confinement operations of similar size over the short term.
"Really, I don't think there is much difference in carbon footprint between grazing and confinement systems for the long term," says Al Rotz, lead author of the paper. "Carbon sequestration can give a major reduction in the short term conversion to pasture systems."
Pilot tests conducted on various farms have also shown that free range cattle fed certain supplemental diets, such as flaxseed and alfafa crops grown on-site, can lower enteric emissions.
So, What and How Should We Eat?
When asked what a carbon-conscious consumer should eat, Pimentel recommends eating mainly plant-based foods like potatoes, broccoli, carrots and beans.
Though he acknowledges that chicken protein and milk from grass-fed livestock is relatively efficient from a greenhouse gas standpoint when consumed in moderation, he advises we should "Go light on the animal protein."