I’m concerned about climate change, and when I’m in the grocery store, I wonder about the environmental footprint of the food I purchase. What is the carbon impact of a hamburger versus chicken salad? Would carbon emissions go down if we began to eat healthier? Together with three other researchers, I set out to track the greenhouse gas emissions associated with the typical US diet throughout the entire food production process from farm to store.
We found that the US food system contributed 985 million tons of CO2eq, or 15% of total US emissions in 2017. About 44% were direct agricultural emissions, including soil management (21%), enteric fermentation (17%), and manure management (7%). Enteric fermentation refers to the methane produced by ruminant livestock, such as cattle, as part of their digestive process. Greenhouse gas emissions (GHGE) per gram of protein for beef are more than six times greater than for pork and more than 20 times greater than for chicken. GHGE from food processing, packaging, transportation, retail trade, and food services are almost as large as GHGE at the farm stage.
At a population level, two vegetarian days per week would reduce US annual GHGE by more than 90 million tons of CO2eq, or the equivalent of the annual GHGE of Sweden and Norway combined.
We wanted to measure the impact of switching from the typical current US diet to one that meets the dietary guidelines set by the US Department of Agriculture and the US Department of Health and Human Services. An omnivore diet includes meat, fish, and dairy products in addition to other plant-based foods. There are many ways to meet the dietary guidelines, and we selected as our healthy omnivore diet the one that is closest to the baseline diet people currently eat. Relative to the baseline diet, our healthy omnivore diet more than doubles both dairy and nuts. It more than triples the quantity of fish and increases the quantity of turkey by 75%. Beef, pork, and chicken decrease by 6%, 16%, and 51%, respectively. Fruits and vegetables increase by almost 60% and 80%, while caloric sweeteners decline by 70%.
Switching to the healthy omnivore diet left GHGE essentially unchanged, so we considered a healthy vegetarian diet as well as another healthy omnivore diet that minimizes fossil fuel consumption in the food system (min-Btu). Switching to the healthy vegetarian the min-Btu diet reduces GHGE by 32% or 22%, respectively. These emission reductions were achieved mainly through quantity and composition changes in the meat, poultry, fish, dairy, and caloric sweetener categories.
So, can you have an impact on the environment by changing your diet? Going vegetarian just twice per week will reduce your GHG emissions related to food production by almost 10%. At a population level, two vegetarian days per week would reduce US annual GHGE by more than 90 million tons of CO2eq, or the equivalent of the annual GHGE of Sweden and Norway combined.