Some years ago I had a discussion with Ian Morris about the approach he took to quantify the social development of East versus West in his book, The Measure of Civilization. So I asked him: Which pre-industrial society was the richest in terms of energy use per capita? I have an answer to this question, which could be quite controversial (and when I offered it to Ian, I had a feeling that I didn’t persuade him).
So what’s your answer? (I have also posed this question on my Twitter)
Let’s make this question precise, so that we all use the same units. We want to measure energy use per time per capita.
Energy is measured in joules and calories (and some other more esoteric units). One calorie is the amount of energy needed to raise the temperature of 1 cubic centimeter of water by 1 degree Celsius (centigrade). 1 calorie is roughly 4.2 joules. Joules are a better unit for energy, compared to calories, because there is a confusion between 1 calorie and 1 kilo-calorie = 1000 calories. But here are the basics (taken from Box 1.3 of Vaclav Smil’s Energy and Civilization). A moderately active adult spends between 2 and 2.7 Mcal (1 million calories) per day which is roughly 10MJ (10 million joules) per day. The unit for measuring energy flow per time is called Watt = J/s (joules per second). The power of a human body, thus, works out to be roughly 100 Watts. Here’s the calculation: 10,000,000 J/(24 hours x 3600 seconds) = 115 W.
So let’s take this number as the base. In a foraging population the main energy use is the human body burning food, but let’s not forget that additional energy is needed to cook food on campfire. Smil (Boxes 1.4 and 2.1) estimates that 1 kg of dry wood contains about 20 MJ and cooking requires less than 0.5 kg of wood per day. This works out to roughly another 100 W. We have just doubled human energy use!
Bushmen getting ready to cook a meal. Source
By 1500 CE various human societies around the globe would be using a number of additional energy sources:
- Burning fuel for cooking and heating houses
- Plowing with animal power (oxen and horses)
- Transportation, using animal power and wind power (sailing)
- Energy-demanding industries: metallurgy, pottery, glass-blowing
- Wind and water mills to mill grain, pump water, etc.
Anything else I am missing?
Now the trick is to convert all those energy-using activities so that we can express them in per capita terms. For example, let’s do a quick calculation of how much iron metallurgy would add to energy use per capita. A peasant needs a steel axe. Let’s say its head weighs 1 kg and needs to be replaced every 5 years. Consulting Box 1.8 in Smil’s book, we find that smelting iron from ore requires 12-20 MJ/kg, and converting it to steel needs further 20-25 MJ. Let’s round it up to 50 MJ per axe head (to account for iron losses during forging). Replacing an axe every 5 years, then, would require 50 MJ/(5 years x 365 days x 24 hours x 3600 seconds) = 0.3 Watts. Well, this doesn’t seem to add a lot (assuming I did the math right).
So here’s the challenge. It’s not enough to name a particularly advanced society. Give me some numbers to show that its energy use was high.