Meat Eaters Guide: Methodology - Environmental Working Group

Meat Eaters Guide: Methodology
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states where the net carbon flux from the soil is zero on average (spatial/temporal average). it should be
pointed out that assumptions about steady state remain the subject of considerable scientific debate.
9. Manure benefits go to crop systems that use it as fertilizer, per the “recycled content” method. No benefits
are accounted for in the animal system that produces the manure. No change to soil carbon stock in crop
systems that use the manure -- under the assumption that the system is at steady state and the net soil
carbon flux is zero on average.
10. While some homes will use electricity for cooking, our model assumes the use of natural gas; further cooking
assumptions are included in Annex B.
11. The size of the large-scale operation is 50,000 birds, smaller than the typical 200,000 in a US poultry operation.
12. While a significant portion of fertilizer is imported and shipped to the United States, emissions from shipping
a minor portion of overall emissions from fertilizer production and delivery. For freight transport by
ocean where the product is not under temperature control, the road transport on either side of the ocean
segment generally dominates the total transport emissions. For example, for 1 Kg of state-of-the-art nitrogen
fertilizer transported 5000 km by ocean and 1600 km by semi-trailer truck, the ocean transport contributes
about 1.3% of the total fertilizer-related emissions at the point of delivery to a farm while the truck
transport contributes 9.1%.
13. We assumed these nominal transport distances for inputs because most agricultural production data
sources do not provide this information. We tested the sensitivities of our assumptions and found that the
final results are quite insensitive to these assumptions. For example, in the case of corn produced in the
Midwest, if the input transport distances changed by +/-25% relative to our assumptions, the cradle-tofarmgate
emissions would change by less than 2 percent (even less if you consider the emissions as a total
percentage of cradle to grave emissions). Transport-related emissions are generally a very minor component
of the overall GHG emissions per Kg of product.
14. Fertilizer production is modeled uniformly on current state-of-the-art technologies per the International Fertilizer
Association and is not country-specific.
15. While many animals are transported far greater distances from their original grazing or confined pasture
lands, we used this distance since our models were based on regional production systems in which all subsystems
(such as cow-calf and feedlot) are in the same state. The sensitivity of final results to this assumption
is very low. The 300 km transport adds less than 0.1 Kg CO 2 e to the cradle-to-gate GHG emissions
of 1 Kg of meat. If we increase this to 1,500 km, it would still represent a very small portion of the overall
carbon footprint.
16. The number was selected somewhat arbitrarily based on average distances from the middle of the country,
where a majority of meat is produced, to major populations centers on either coast.
Environmental Working Group Meat Eaters Guide: Methodology 2011