Energy Return On Investment is a key indicator. At the start, one barrel of oil returned 1200 more. Today one barrel yields about 20 more. It is almost a wash. Pre-1917 Russian farmers returned 145 calories of food value for 15 calories burned in production. Modern agriculture burns 20 calories for every calorie of food produced. When oil EROI approaches zero, modern farming methods become impossible. Hydro-electric is my favorite source of power.
I’ve long ago considered the EROI as not only a key indicator, but far superior to any other measure.
At the end of the day, you can’t eat gold or do anything else with it other than show off.
Gold is superficial.
Energy is life.
The numbers you use are intriguing and I’d like to know your source.