Page 65 - Environment: The Science Behind the Stories

Calculating Ecological Footprints

The second law of thermodynamics has profound implica- 10 Calories of plant material. So when we raise animals for
tions for human impacts on the environment, as it affects the meat using grain, it is less energetically efficient than if we
efficiency with which we produce our food. In ecological ate the grain ourselves.
systems, a rough rule of thumb is that when energy is trans- Humans are considered omnivores because we can eat
ferred from plants to plant-eaters or from prey to predator, both plants and animals. The choices we make about what
the efficiency is only about 10% (p. 100). Much of this inef- to eat have significant ecological consequences. With this in
ficiency is a consequence of the second law of thermodynam- mind, calculate the ecological energy requirements for four
ics. Another way to think of this is that eating 1 Calorie of different diets, each of which provides a total of 2000 dietary
meat from an animal is the ecological equivalent of eating Calories per day.

Diet Source of Calories Number of Calories Ecologically equivalent Total ecologically
consumed Calories equivalent Calories
100% plant Plant
0% animal Animal
90% plant Plant 1800 1800 3800
10% animal Animal 200 2000
50% plant Plant
50% animal Animal
0% plant Plant
100% animal Animal

1. How many ecologically equivalent Calories would it take 3. What percentages of the Calories in your own diet do you
to support you for a year for each of the four diets listed? think come from plant versus animal sources? Estimate
2. How does the ecological impact from a diet consisting the ecological impact of your diet, relative to a strictly
strictly of animal products (e.g., milk, other dairy prod- vegetarian one.
ucts, eggs, and meat) compare with that of a strictly vege- 4. Describe some challenges of providing food for the
tarian diet? How many additional ecologically equivalent growing human population, especially as people in many
Calories do you consume each day by including as little poorer nations develop a taste for an American-style diet
as 10% of your Calories from animal sources? rich in animal protein and fat.

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