Diet, Energy, And Global Warming

Abstract

The energy consumption of animal- and plant-based diets and, more broadly, the range of energetic planetary footprints spanned by reasonable dietary choices are compared. It is demonstrated that the greenhouse gas emissions of various diets vary by as much as the difference between owning an average sedan versus a sport-utility vehicle under typical driving conditions. The authors conclude with a brief review of the safety of plant-based diets, and find no reasons for concern.

Generated Summary

This study investigates the environmental impact of dietary choices, specifically comparing the energy consumption and greenhouse gas (GHG) emissions associated with plant-based and animal-based diets. The research employs a comparative analysis, utilizing data on food production, transportation, and energy consumption from various sources, including the U.S. Department of Energy and FAOSTAT. The methodology includes calculations of energy efficiencies, GHG emissions, and the impact of different dietary compositions on the overall environmental footprint. The scope of the study encompasses the entire food system, from agricultural production to transportation and waste management, with a particular focus on the implications of dietary choices for climate change. The study aims to quantify the GHG burden of various diets, highlighting the differences between plant-based and animal-based options, and assessing the safety of plant-based diets from a public health perspective.

Key Findings & Statistics

• In 1999, the total energy used in U.S. food production was estimated at 10.2 × 10¹⁵ BTU/yr, accounting for 10.5% of the total energy used.
• In 2002, the food production system accounted for 17% of all fossil fuel use in the United States.
• The energy used for food production accounted for 10.5% of the total energy used in 1999.
• Annual U.S. per capita vehicle miles of travel were 9848 in 2003, with 8332 miles traveled by cars, of which an estimated 63% are traveled on highways.
• The 2005 vehicle miles per gallon (mpg) range is bracketed by the Toyota Prius’ 60:51 (highway:city) on the low end and by Chevrolet Suburban’s 11:15.
• Depending on the vehicle model, an American is likely to consume between 1.7 × 10⁷ and 6.8 × 10⁷ BTU/yr for personal transportation.
• The average American uses roughly 4 × 10⁷ BTU/yr for food.
• The U.S. food production system produced 3774 kcal per person per day in 2002, or 1.4 × 10¹⁵ BTU/yr nationwide.
• Energy efficiency is defined as the percentage of fossil fuel input energy retrieved as edible energy.
• The estimated energy efficiency of protein in animal products varies from 0.5% for lamb to ~5% for chicken and milk to 3% for beef.
• The weighted mean efficiency of meat in the American diet is 9.32%.
• The average American diet, with 27.7% of calories from animal sources, is shown, along with the added CO2 it corresponds to (assuming average efficiency of 13.7%), 0.726 ton.
• The study calculates that a person consuming the average American diet, with average caloric efficiencies of the animal- and plant-based portions of the diet, releases 701 kg of CO2 yr beyond the emissions of a person consuming only plants.
• The study finds that, with 291 million Americans in 2003, non-CO2 emissions amount to 800 kg CO2-eq per capita annually in excess of the emissions associated with a vegan diet.
• The red meat, mean American, fish, and poultry diets derive 41% and 5% of their animal-based calories from dairy and eggs.
• The average American diet, with a = 0.277 (with 27.7% of calories from animal sources) is shown, along with the added GHG burden associated with this diet, ~1.5 ton CO2 per person per year.
• The study estimates that the GHG burden for the animal-based portion of the U.S. collective diet is roughly 1.485 ton CO2-eq per person per year × 291 million Americans ≈ 432 million ton CO2-eq yr nationwide, or ~6.2% of the total.
• The value of 800 kg CO2-eq yr due to non-CO2 emissions represents the composition of the actual mean American diet.
• The value of 800 kg CO2-eq yr due to non-CO2 emissions computed above represents the composition of the actual mean American diet.

Other Important Findings

• The link between observed rising atmospheric concentrations of CO2 and other GHGs, and observed rising global mean temperature and other climatic changes, is not unequivocally established.
• Modifying aspects of our lives is required in order to reduce GHG emissions.
• Food production, a function of our dietary choices, represents a significant and growing energy user.
• There exists an order of magnitude parity in fossil energy consumption between dietary and personal transportation choices.
• Food production also releases non-CO2 GHGs unrelated to fossil fuel combustion.
• The study defines and considers several semirealistic mixed diets: mean American, red meat, fish, poultry, and lacto-ovo vegetarian.
• The study calculates the energy and GHG impact of each diet over a range of this fraction, 0% ≤ a ≤ 50%, where a = 0 corresponds to a vegan diet.
• Plant-versus animal-based diets is a principal source of such variability.
• The notable equality of fish and red meat efficiencies reflects 1) the large energy demands of the long-distance voyages required for fishing large predatory fishes such as swordfish and tuna toward which western diets are skewed, and 2) the relatively low energetic efficiency of salmon farming.
• The non-CO2 GHG emissions per kcal vary by as much as a factor of 70 for the animal-based food items considered.
• Adding the non-CO2 GHG emissions more than doubles the impact of the mean American diet at mean (27.7%) animal fraction, from 701 kg CO2-eq per person per year in Figure 2 based on fossil fuel input alone to nearly 1.5 ton CO2-eq per person per year in Figure 3 taking note of fossil fuel inputs as well as non-CO2 emissions.
• It only requires a dietary intake from animal products of ~20%, well below the national average, 27.7%, to increase one’s GHG footprint by an amount similar to the difference between an ultraefficient hybrid (Prius) and an average sedan (Camry).
• For a person consuming a red meat diet at ~35% of calories from animal sources, the added GHG burden above that of a plant eater equals the difference between driving a Camry and an SUV.

Limitations Noted in the Document

• The study acknowledges that the link between observed rising atmospheric concentrations of CO2 and other GHGs, and observed rising global mean temperature is not unequivocally established.
• The study ignores non-CO2 GHGs produced during fossil fuel combustion.
• The study focuses on two main non-CO2 GHGs emitted by agriculture, methane and nitrous oxide, while also noting that the exact partitioning of nitrogen fertilization into animal feed and human food is a complex bookkeeping exercise beyond the scope of this paper.
• The study’s estimate of the GHG burden exerted by animal-based food production may be a lower bound due to the exclusion of certain factors.
• The study acknowledges that the analysis of non-CO2 GHG emissions requires intermediate steps, as available data are for specific farm animals, not individual food items.
• The study notes that the study’s objective is to compute the difference between various mixed diets and an exclusively plant-based, vegan, diet.

Conclusion

The central argument of this paper is that dietary choices have a significant impact on greenhouse gas emissions, comparable to the impact of personal transportation choices. The study demonstrates that animal-based diets, particularly those with a high proportion of red meat, contribute substantially more to GHG emissions than plant-based diets. This finding is supported by the analysis of energy consumption in food production, the varying efficiencies of different food sources, and the impact of non-CO2 GHG emissions. The difference between the added GHG burden of a red meat diet and a plant-based one is comparable to the difference between driving a Toyota Camry and an SUV. This emphasizes that dietary choices have a discernible effect on one’s planetary footprint. The study emphasizes the importance of considering both direct and indirect emissions, including CO2 emissions from fossil fuel combustion, and methane and nitrous oxide emissions. The findings suggest that by shifting towards plant-based diets, individuals can significantly reduce their environmental impact and contribute to the mitigation of climate change. The results clearly demonstrate the primary effect of one’s dietary choices on one’s planetary footprint, an effect comparable in magnitude to the car one chooses to drive. The study briefly addresses the public health safety of plant-based diets, and finds no evidence for adverse effects, indicating that such diets are at the very least just as safe as mixed ones, and are most likely safer. The study concludes that the total greenhouse gas emissions from the animal-based portion of the U.S. collective diet is roughly 6.2% of the total U.S. greenhouse gas emissions. The authors state, “These results clearly demonstrate the primary effect of one’s dietary choices on one’s planetary footprint, an effect comparable in magnitude to the car one chooses to drive.”