Interesting article in Harper's Magazine "The Oil We Eat"

Quote:

The journalist's rule says: follow the money. This rule, however, is not really axiomatic but derivative, in that money, as even our vice president will tell you, is really a way of tracking energy. We'll follow the energy.
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If you follow the energy, eventually you will end up in a field somewhere. Humans engage in a dizzying array of artifice and industry. Nonetheless, more than two thirds of humanity's cut of primary productivity results from agriculture, two thirds of which in turn consists of three plants: rice, wheat, and corn. In the 10,000 years since humans domesticated these grains, their status has remained undiminished, most likely because they are able to store solar energy in uniquely dense, transportable bundles of carbohydrates. They are to the plant world what a barrel of refined oil is to the hydrocarbon world. Indeed, aside from hydrocarbons they are the most concentrated form of true wealth--sun energy--to be found on the planet.

Yes, he's grasped an important truth: for agriculture to become viable over hunter-gatherer lifestyle it has to provide food in winter (or whatever the off season is). Grain is a pain to harvest and process (even in the simple sense of de-husking, then there is milling if you want flour). There must be some advantage to make this worthwhile and that is its storage ability and ease of transport relative to food value.

Ultimately the carrying capacity is determined by its weakest link; for many societies that is probably its winter / drought food availability.