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Greenhouse
Gas Emissions
The
statistics on greenhouse gas emissions were
derived from
numbers in “Diet,
Energy, and Global Warming,” by Gidon Eshel
and
Pamela A.
Martin of the University
of Chicago.
It was published in Earth Interactions, volume 10 in 2006. The authors
calculated the greenhouse gas emissions produced by various diets and
compared
the environmental benefits to driving hybrid versus standard cars. We
figured out the daily greenhouse gas outputs from the authors' yearly
figures on animal-product-based and animal-product-free diets and then
assumed that the average lunch would be about 28% of the daily figures.
The authors also calculated the average yearly CO2 output for the
Toyota
Prius and Camry, which we broke down to daily figures to complete the
picture.
Water
The
water statistics were derived from cubic meters per ton figures in the
appendices of a 2004 UNESCO Institute for Water Education report called
the Water Footprints of Nations, available at http://www.waterfootprint.org.
We
looked at recipes and then online at restaurant menu information to
figure out the weight of the relevant ingredients, for example about
3oz of beef for a typical hamburger or about two and a half ounces of
dry beans per serving of black bean soup, from which it was pretty
simple to
get the difference in gallons of water used per
serving.
Land
The
land statistics were derived from numbers on
land use (that animal products take 6 to 17 times as much land as soy
to produce the same amount of protein) in
“Quantification
of the environmental impact of different dietary protein choices”
by Lucas Reijnders and Sam Soret, which appeared in a 2003 supplement
to the American Journal of Clinical Nutrition
and on the protein output per acre
for soy and for peanuts reported in the 1996 edition of Food,
Energy, and Society edited
by Pimentel and Pimentel. We used these numbers to figure out
the square feet per serving and then compare animal-product foods to
animal-product-free foods.
More Information
We're
happy to share more information on how we got to our numbers beyond
what we've posted on the website. If you have questions about our
methods and calculations, please don't hesitate to email
us.
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