Understanding the Carbon Footprint of Food: A Closer Look
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Chapter 1: Analyzing Carbon Footprints in Food Production
What is the carbon footprint associated with food items? Are we addressing the right scientific questions? Here, I reflect on the presentations from Our World in Data (OWiD) and their sources.
For the past thirty years, misconceptions regarding methane emissions from livestock have increasingly influenced climate discussions, often leading to the flawed argument that reducing meat consumption is a viable climate strategy. OWiD's initial presentation relied on the Global Warming Potential over 100 years (GWP100), which incorrectly assessed methane's impact, failing to acknowledge that livestock methane contributes minimally to global warming.
I commend OWiD for collaborating with climate scientist Michelle Cain from Oxford Martin to produce an updated version of their GWP* presentation. Although this revision is a marked improvement, I still question the relevance of the remaining gray bars in the diagrams (Figure 1). Since GWP* indicates that livestock methane has a negligible warming effect, these bars could be eliminated. Instead of focusing on volume-based greenhouse gas (GHG) "carbon" footprints, the climate conversation would benefit from an analysis of the actual impacts of various GHGs. We now have the tools to engage more rationally in climate mitigation, guided by a coherent warming-equivalent metric.
However, examining both the original and revised OWiD presentations from an agricultural perspective, I find several issues concerning the red bars that contribute to my cognitive dissonance. How accurately do these presentations reflect the true climate impact of food items?
Drawing from the research paper "Reducing food's environmental impacts through producers and consumers" (Poore & Nemecek, 2018), I question the relevance of these figures at the farm level. Even when enteric methane warming is excluded, how reliable is the remaining data?
Section 1.1: LULUCF-Based Assumptions
Surprisingly, the presentations show significantly higher land-related emissions from livestock than from crops, which contradicts conventional agricultural knowledge. Typically, one would expect livestock-related land emissions to be lower, while crop-related emissions would be higher. Additionally, it appears there is no acknowledgment of the maintenance of grassland carbon dioxide (CO2) soil stocks.
The source paper seems to rely on a mix of actual data (land areas and yields), assumptions, and projections regarding climate and environmental impacts linked to various production methods. These assumptions often come with considerable error margins and uncertainties. The results might already be skewed, and scaling them to a global level could exacerbate these inaccuracies.
These issues will be discussed in detail, starting with OWiD's underlying assumptions, which can be summarized as follows:
Land Use Change
Livestock agriculture is typically characterized by stability. Most grasslands have developed through sustained use over decades, centuries, or even millennia. Herd sizes tend to remain constant annually, and land use changes—like converting forests or peatlands into grasslands—are uncommon unless there is a significant increase in herd size. While this may occur in regions expanding their livestock operations, emissions related to land use changes in livestock farming are generally minimal worldwide.
Pasture Management
In both versions of the presentation, it is crucial to consider the climate implications of vast land areas used for ruminants. Instead of merely asking, "How many hectares?" we should explore "What roles does this land serve, and how do they impact the climate, environment, and food security?"
Largely, grasslands utilized for livestock are marginal lands, unsuitable for crop cultivation. Therefore, they do not compete with the production of plant-based foods. Furthermore, these perennial grasses have deep root systems that sequester significant carbon over time.
Liming, Fertilizing, and Pasture Management
Meadows and pastures are less frequently tilled compared to crop fields, resulting in less intensive management. Fertilization in meadows often relies on manure rather than chemical fertilizers, which emit substantial CO2 during production. Thus, the assumptions in the presentations appear to reflect the inverse of typical agricultural practices.
Chapter 2: Waste and Emission Considerations
What about the emissions related to slaughter and food waste? The presentation cites high wastage rates during slaughter and spoilage of fresh animal products throughout the supply chain. However, the parts of the animal not consumed are often repurposed for various industries, leading to minimal actual waste.
Food wastage, in general, is a critical topic. The FAO estimates that meat contributes the least to global food waste compared to other food categories. This highlights the need to differentiate between the volume of food waste and its climate impacts. The misconception that meat waste emissions are comparable to those of vegetables is based on outdated metrics, which can mislead discussions about food production and its environmental footprint.
In summary, OWiD's presentations appear to overstate certain aspects while overlooking others, leading to a biased depiction of agricultural reality. The call for improved data quality and accuracy in agricultural climate research is essential to understanding the true environmental impact of food production.
References
- Our World in Data, 2020 Environmental impacts of food production
- Poore and Nemecek, 2018 Reducing food's environmental impacts through producers and consumers
- FAO, 2015 Food wastage footprint & Climate Change