If I’d used this number instead of my rough guess, the energy contribution
of the chicken would have been bumped up a little. But given that
the mixed-meat diet’s energy footprint is dominated by the beef, it really
doesn’t matter that I underestimated the chickens. Sources: Subcommit-
tee on Poultry Nutrition, National Research Council (1994), www.nap.edu/
, MacDonald (2008), and www.statistics.

77let’s assume you eat half a pound (227 g) a day of meat, made up of equal
quantities of chicken, pork, and beef
. This is close to the average meat con-
sumption in America, which is 251 g per day – made up of 108 g chicken,
81 g beef, and 62 g pork (MacDonald, 2008).

78The embodied energy in Europe’s fertilizers is about 2 kWh per day per per-
. In 1998–9, Western Europe used 17.6 Mt per year of fertilizers: 10Mt of
nitrates, 3.5 Mt of phosphate and 4.1 Mt potash. These fertilizers have energy
footprints of 21.7, 4.9, and 3.8 kWh per kg respectively. Sharing this energy
out between 375 million people, we find a total footprint of 1.8 kWh per day
per person. Sources: Gellings and Parmenter (2004), International Fertilizer
Industry Association [5pwojp].

Farming in the UK in 2005 used an energy of 0.9 kWh per day per person.
Source: Warwick HRI (2007).

79A bag of crisps has an embodied energy of 1.4 kWh of fossil fuel per kWh of
chemical energy eaten
. I estimated this energy from the carbon footprint of
a bag of crisps: 75 g CO2 for a standard 35 g bag [5bj8k3]. Of this footprint,
44% is associated with farming, 30% with processing, 15% packaging, and
11% transport and disposal. The chemical energy delivered to the consumer
is 770 kJ. So this food has a carbon footprint of 350 g per kWh. Assuming that
most of this carbon footprint is from fossil fuels at 250 g CO2 per kWh, the
energy footprint of the crisps is 1.4 kWh of fossil fuel per kWh of chemical
energy eaten.

The typical diet has an embodied energy of roughly 6 kWh per kWh eaten.
Coley (2001) estimates the embodied energy in a typical diet is 5.75 times the
derived energy. Walking has a CO2 footprint of 42 g/km; cycling, 30 g/km.
For comparison, driving an average car emits 183 g/km.

Walking uses 3.6 kWh per 100 km. A walking human uses a total of 6.6 kWh
per 100 km [3s576h]; we subtract off the resting energy to get the energy
footprint of walking (Coley, 2001).

Further reading: Weber and Matthews (2008).