The energy we use to power our civilization has two sources: solar radiation and radioactive decay. In turn, some of the solar radiation is converted into glucose by photosynthesis. The glucose is stored in plants and in their parasites and symbiotes. Animals, including humans, eat the plants to grow muscles and brains. Finally, humans use muscle power, guided by brain power, to do the work of human society. Thus, we can say that the muscle and brain power we use to do the work of society derives from the short-term storage of solar radiation by plants.

This linear process branches where plants convert some of the glucose into cellulose for longer-term storage as the chief component of the woody parts of plants. At some point, perhaps as recently as 100,000 years ago, humans learned to unlock the energy stored in wood by burning it. Eventually, perhaps as recently as 7,000 years ago, humans recruited animals to increase the muscle power available for work.

The development of agriculture, about 8,000 years ago, enabled humans to establish larger settled groups and eventually cities. Indeed, agriculture sufficiently productive to support larger groups seems to require the hierarchical social arrangements of cities. That productivity was based on human and animal muscle power.

From the founding of cities, about 6,000 years ago, to the middle of the 17th century, 400 years ago, this was the state of energy usage: the energy from photosynthesis of solar radiation stored in plants drove all human activities. Wind and falling water, near real-time uses of solar radiation, added a small amount of additional power. In modern terms, the energy available for human activity beyond sustenance was all photosynthetic solar, supplemented by a little wind and falling water. Succinctly, our civilization was energized completely by short-term storage and real-time exploitation of solar radiation.

Over that period, there were gradual improvements in the yields of agriculture, the increase of muscle power by domesticating animals, and improvements in using wind and water power. These improvements supported modest increases in leisure for humans to engage in the arts and sciences of civilization. More accurately, maybe 5% of the population, mostly men, could spend time in activities other than providing the basics of living.

Sometime in the 17th century, the middle of the "Little Ice Age", the people in the cold climate of England began supplementing the burning of wood with coal, solar energy stored about 100 million years ago. People in China had used coal earlier, but it had not become an important source of energy. At the same time, farmers in Western Europe introduced green manuring, rotating food crops with plants having nitrogen-fixing root nodules. This innovation doubled the productivity of food crops.

For the next 400 years, the increasing productivity of agriculture paired with the increasingly effective extraction of energy from coal, then oil and gas, drove improvements in human well-being. We all know how this played out: faster and cheaper transportation, cast iron and steel for tools and structures, development of the internal combustion engine, machinery to enhance the productivity of agriculture and manufacturing, and eventually tools and systems to free women from much of the exhausting work of sustaining a home. By the late 20th century, the fraction of the population working in agriculture had decreased from 95% to 3%, except in those parts of the world where social arrangements inhibited the introduction of modern agriculture.

One of the most notable, but least well-known, achievements in these centuries was the Haber-Bosch process (1910) for fixing nitrogen. This process requires natural gas and large quantities of electrical, heat, and mechanical energy, all unavailable until the end of the 19th century.  The resulting explosion of agricultural productivity led to the 20th century population explosion.

We are now moving into the age of nuclear power to replace much of the fossil fuel power. The development of nuclear fission as a source of energy is presently in a stage comparable to the development of coal at the beginning of the 18th century. In currently operating nuclear power plants, only 5% of the energy in the uranium fuel is used to make electricity, similar to the efficiency of the earliest steam engines. The transition to fission energy may have consequences as great as the steam engine and the Haber-Bosch process. It appears that the widespread replacement of fossil fuels with current nuclear fission technology may, in the near-term, increase 100-fold the energy available from muscle power alone. Nobody knows what the future will bring, just as nobody in 17th century England knew what the consequences would be of switching from wood to coal for heat.

For 8,000 years, human sustenance and activities depended on agriculture constrained by insufficient fixed nitrogen and the limitations of muscle power. Beginning 400 years ago, the increasing availability of fixed nitrogen combined with mechanization led to a 100-fold increase in agricultural productivity. At the same time, the introduction of fossil fuels led to a 30-fold increase in the energy available for productive work. When humans were relieved of the drudgery of hoeing a field and carrying water from a stream, they could devote themselves to improving agriculture and energy availability, indulging in arts and sciences, and managing our garden planet.

My answer to the question implied by this essay’s subtitle is that humans achieved flourishing societies by:

I call on you to raise a glass to our ancestors who built the affluence we enjoy. Of course, the job is not done: a great many humans do not enjoy affluence, so I also call you to aid them in creating it.

     George

Crescat scientia, vita excolatur.