The Fire

Societies need energy in order to sustain themselves and their members. This energy comes in two forms: fuel and food. These are continuous: they are both means of energy acquisition consumed for the same purpose, the maintenance of a complex society. The energy sources that sustain a society—whether fuel or food—must have a sufficiently high aggregate energy returned on energy invested (EROI). The EROI of a source is the energy acquired from a source divided by the energy that the society had to invest in acquiring it. Once the EROI of a society’s energy sources drops below a certain threshold, societal collapse often results: the breakup of that society and the emergence of new, simpler societies. Calculations suggest that maintenance of a society recognizably similar to our own vis-à-vis socioeconomic parameters requires energy sources with EROIs in the 11–14 range. Maintenance of certain markers of liberal democracies may require higher EROIs, in the 20–30 range.