Implications of Future US Diet Scenarios on Greenhouse Gas Emissions
Linkages between diet and environmental impact have been repeatedly emphasized at the global and national level, with an indication that shifts in diet, typically toward more plant-based foods, can lead to significant reduction in environmental impact. In this study, we explore the effect on food system greenhouse gas emissions (GHGE) of a hypothetical reduction in the consumption of animal-based foods in the US diet and a replacement with plant-based foods.
USDA’s Loss Adjusted Food Availability (LAFA) dataset, a top-down estimate of the per capita consumption of commodity foods in the US, is used to represent the baseline, or current, US diet. Greenhouse gas emission factors previously compiled from life cycle assessment literature were linked to these commodity foods to estimate the per capita GHGE associated with agricultural production of the average diet. A number of dietary scenarios projected to 2030 were then developed:
- The baseline average diet remains unchanged to 2030
- Meat and poultry consumption increases per USDA projections
- Consumption of animal-based foods (red meat, poultry, fish/seafood, eggs, dairy, and animal based fats) decreases by 50%, and is substituted with plant-based foods
- Same as scenario 3, but beef decreases by 90%, instead of 50%.
The total emissions associated with producing the average US diet amounts to 5.0 kg CO2 eq. per person per day. Whereas red meat (beef, pork, lamb) represents 9% of the calories available from this diet, it contributes 47% of the GHGE. All animal-based foods combined (red meat, poultry, fish/seafood, eggs, dairy, and animal based fats) represent 82% of the baseline diet GHGE. According to LAFA data, the average American consumed 133 pounds of red meat and poultry in 2016. USDA projects slight increases in per capita red meat and poultry consumption in the US in 2028 (scenario 2); assuming other foods unchanged, this raises the carbon footprint to 5.14 kg CO2 eq. per person per day.
Cutting the intake of all animal-based foods by half and replacing with equivalent quantities of plantbased foods (scenario 3) results in a 35% decrease in GHGE from the baseline, to 3.3 kg CO2 eq per person per day. Under this scenario 3, red meat represents 36% of the total emissions. Further reducing consumption of beef to only 10% of the baseline value, and subsequent replacement with plant-based proteins (scenario 4), cuts the diet-related emissions to 2.4 kg CO2 eq per capita per day, a 51 % decrease from the baseline diet. Under this final scenario 4, the average American consumes 50.1 pounds of meat and poultry per year.
Using population projections from the US Census Bureau, an unchanged diet would result in 646 million metric tonnes CO2 eq. (MMT) in 2030, whereas scenario 3 – replacing 50% of all animal-based foods with plant-based alternatives – leads to 224 MMT less emissions per year in 2030, a reduction equivalent to the annual emissions of 47.5 million of today’s average passenger vehicles. If we assume a linear transition from the 2016 diet to 2030 projections, this target of 50% substitution results in an estimated cumulative reduction of 1634 MMT. By further replacing 90% of beef, the cumulative emission reduction increases to 2408 MMT.
Although reliant on a number of simplifying assumptions, this diet projection exercise emphasizes the important role that changes in diet can play in climate action. An annual emission reduction of 224 MMT represents 24% of the reduction from 2017 emissions required to meet the US Intended Nationally sizable reductions are possible without complete elimination of animal-based foods from the diet can make diet shift strategy more palatable. Such changes, however, will require the concerted efforts of policymakers, the food industry and consumers. The projection scenarios presented here point to the urgency of such efforts, as decisions made now will have a cumulative impact over the next decade.