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Effects of a Plant-Based Diet

Professor Gidon Eshel
Dept. of Geophysical Sciences, University of Chicago

Strengthening evidence exists to prove that global warming is primarily due to rising atmospheric greenhouse gas concentrations from human activities. This effect makes personal voluntary choices a leading edge in the battle to preserve our threatened global habitat. While one hears a lot about transportation choices, only recently have we turned our collective climate change conscience to food as an option to reducing global warming effects.

Consider the following example. Belinda and Melinda are of similar age, weight, height, and physical activity level. While having identical daily caloric consumption, Melinda eats only plants (vegan) while Belinda eats the average American diet, with roughly a third of her total calories from animal sources. Belinda’s global warming contribution is dramatically larger than Melinda’s; her diet is responsible for the extra emission of approximately 1500 kg of greenhouse gases (GHGs) a year. However, if all US persons went Melinda’s way, the US greenhouse gas emissions would drop by 6%.

Plant-based foods yield, on average, twice as much edible energy as the fossil-fuel based energy used during production. The corresponding number for animal-based foods is 0.1 (e.g., we get one edible Kcal for each ten fossil-fuel input Kcals). Therefore, plant-based foods have a factor of 2/0.1 = 20 edge over animal-based ones. Given this massive efficiency disparity of plant- versus animal-based foods, imagine what planetary effect we could have in switching from an animal- to a plant-based diet?!
Our recent paper titled “Diet, Energy and Global Warming” addresses this very issue and demonstrates that with the average American diet, an additional 700 kg of CO2 emissions are created from fossil fuel energy consumption per year. These emissions are from direct fossil fuel consumption for necessary treatment of manure from meat production and, during the animals’ digestion, ruminants also produce methane, a powerful greenhouse gas.

In addition, combining non-CO2 greenhouse gas emissions, the difference between the average American diet and the vegan diet increases to 1500 kg CO2-equivalent. This increase is significant considering, for example, under normal driving conditions, the difference between driving a Prius or a Camry is just over a ton of CO2. That is, switching from the average American diet to a vegan diet is 50% more effective in reducing your global warming contribution than switching from a Camry to a Prius!

Visit the full study by Gidon Eshel and Pamela Martin at: geosci.uchicago.edu/~gidon/papers/nutri/nutri.html.

Plant-based diet

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