Are cows really worse for the climate than cars?
The impetus for this question can usually be traced back to a 2006 United Nations Food and Agriculture Organization (FAO) report entitled “Livestock’s Long Shadow”. Actually, the controversy usually traces back to the FAO’s news release for the study entitled “livestock a major threat to environment” that has undergone significant mutation as it has gone viral on the internet. (The most recent “resurfacing” of the controversy appeared in an April 2012 NY Times Op-Ed by James McWilliams entitled “the Myth of Sustainable Meat” that Joel Salatin of Polyface Farm in Virginia wrote a rebuttal to – definitely worth reading.)
There are a number of misunderstandings (both pro- and anti-livestock) of the study circulating, but the most common misunderstanding I encounter is the idea that digestive methane released by cows has a greater global impact than the transportation sector – which is simply not accurate. The second most common misunderstanding I encounter is that the FAO’s findings were new information – which is also simply not accurate.
What the FAO report actually does is inventory and analyze all direct and indirect emissions that can potentially be attributed to global livestock production and concludes that on a life-cycle basis global livestock production accounts for 18% of global greenhouse gas emissions on a CO2 equivalent basis (global transportation is 17%). Direct and indirect emissions they inventory include methane emissions from digestion (enteric fermentation), methane and nitrous oxide emissions associated with manure, CO2 and nitrous oxide emissions associated with feed crop production, CO2 emissions associated with fertilizer production and fuel use in crop production, emissions from livestock processing and food transportation, and CO2 emissions related to land-use changes.
None of this represents new primary scientific data; it was just a new approach to organizing, attributing, and presenting existing data in a different way than had been done before (see Climate Change FAQ 1 for discussion on implications for different approaches to GHG emissions inventories). Note that the World Bank (2007) indicated that agriculture and food in total account for between 26 and 35% of total global GHG emissions, depending on assumptions and attribution.
Guess what? Feeding the global population has a large impact on GHG emissions!
So what does all this mean, from a scientific perspective?
First and foremost, it is important to recognize and appreciate that while inventories and assessments like the FAO report are useful in illustrating the state of current conditions, they should never be used as the sole basis for recommended strategic policy. This is because the inventory methodology has severe limitations and is not an appropriate methodology for projecting the impact that changes in policy or management will have on future conditions.
If our ultimate concern is reducing GHG emissions associated with human food consumption, we need to be able to project which complement of actions will lead to an actual reduction in emissions when all other consequent effects are accounted for. Economists call this equilibrium – because every societal action is interdependent on other actions. What we know from these types of studies is that isolated actions often don’t achieve the desired change and frequently have the opposite outcome on the condition of concern that is intended. For example, increasing vehicle fuel efficiency standards makes it less expensive to drive, incentivizing increased vehicle miles traveled and consequently maintaining total fuel consumption and emissions patterns.
Second, in conducting these types of inventories a number of assumptions and limitations need to be applied in order to keep a study manageable. Generally speaking, these studies aggregate data on the basis of reported average values and extrapolate globally. This is exactly why universities train graduate students in research methodology – to understand the limitations of research methodologies in order to avoid making inappropriate applications of the research findings. One of the most significant sources of error in research is aggregating data from individual experiments for global generalization or translation to other conditions. The key way this plays out in the FAO report is that they don’t provide any substantive comparative assessment of management – outside of extensive vs. intensive production systems. Instead, the authors address “alternative management” through a set of recommendations based on literature review that they clearly articulate could lead to significant improvement in the sustainability of global livestock production.
Third, for some time there has been a growing appreciation amongst many scientists working on sustainable agriculture systems that the re-integration of livestock and crop production systems is likely to be a critical strategy for improving overall agricultural sustainability and resiliency. The reasons for this include the role livestock can play in improving carbon and nutrient cycling, soil quality, crop rotation and diversity (animals can eat a far wider range of plants than humans), and improving and diversifying farm income. As one colleague of mine often points out, we never see a sustainable “natural” ecosystem that doesn’t integrate plant and animal communities.
Finally, we also need to appreciate the clear difference between sustainable pathways for food (and livestock) production in comparison with transportation (or energy) systems. It’s possible to have zero-emission transportation and energy systems – because the production of energy isn’t necessarily tied to global carbon and nitrogen cycles. However, food is composed of organic material and by definition is integral to global carbon and nitrogen cycles. While we can always make improvements in the greenhouse gas emissions from our production systems, no matter how sustainable we are food will always have a carbon footprint. So, we’re not off the hook for our cars yet….