Because, in terms of the quality of life that people in rich countries now experience, that’s kind of what having access to energy is like.

Here’s how … If you spent 10 hours a day, 300 days a year, jogging on a treadmill, you’d expend about 1 gigajoule of energy (at 100 watts): a reasonable proxy for a hard year’s work. The average primary energy consumption of a European is around 150 gigajoules per year. So, energy use in Europe use is a bit like every man, woman and child having 150 full-time servants.

You have to go back a long way to find people enjoying that level of help. Henry VIII (1491- 1547) was attended by nearly 1,000 servants when he stayed at his Hampton Court palace. But that’s a) 500 years ago and b) unusual.

Americans each consume more like 300 gigajoules per year, which is like twice the number of servants that Europeans (don’t) have. Sort of.

Sources: Shell, World Bank, The National Archives