Humans as carbon dioxide generators
Someone asked me how much we, as humans, contribute to the
greenhouse effect, by breathing out carbon dioxide.
It's not a difficult calculation. We need the weight of
food consumed per day and the carbon content. It has to be the
dry mass - what the food would weigh if it was dehydrated - because
water (the main constituent) contains no carbon.
Here are my estimates, wet weight:
Protein (meat, eggs, etc): 8oz.
Carbohydrate: 1 lb (bread, potatoes, other root veg, cakes)
Leafy vegetables don't weigh much so we can miss those out.
Fat - 2oz.
We won't be far out if we say 1.5lbs total.
The dry weight
would be about a quarter to a third of this - say half a pound.
The approximate composition from an energy point of view
would be CH2O. With masses C=12, O=16, H=1, carbon
forms 12/30ths of the total, or two fifths. So we have
a fifth (1/2 x 2/5) of a pound of carbon per day.
Multiply by 365 - we get 72 lb.
Multiply by about 3.5 for mass of CO2: 250lb.
In metric units this is around 125 kg, or 0.125 metric tons -
an eighth of a ton.
This represents a thirtieth of the carbon
dioxide "output" of a member of the UK.
Nigel Deacon / Habitat21 website
