1. The Human Command of Energy Through Time
In the distant human past, pre-fire and pre-agriculture, humans did all work with their own bodies. In such a setting, each human would need about 100 watts of power for sustenance. (2400 watt-hrs/day or 2.4 kWh)
But eventually, humans learned to accomplish more with their efforts:
fire for cooking and hunting
tools, domesticated animals, and agriculture
By 1800 the world average per person power utilization had quintupled to ~500 watts, (5 energy servants):
water and wind power, some coal
By 2000, global average was 20 energy servants, in the US, 100+:
combustion of fossil fuels (~87% from fossil fuels)
Are the global and US rates and sources sustainable?

2. Externalities: costs of an economic activity that are not directly paid for by the buyers and/or sellers of the activity
Energy externalities include: