The History of Energy Since 10,000 B.C.

Physicists agree that the total quantity of energy in the universe is constant. On Earth, energy is held in rough balance: What arrives from the sun as radiant energy is equivalent to what dissipates into space as heat.

Energy can neither be created nor destroyed. Yet, we commonly speak of energy production or consumption.

The word “energy” is imprecise. The stuff is hard to measure. All our energy, ultimately, is nuclear energy, in that it comes from a nuclear fusion reaction in the sun.

It exists on earth in several forms, the important ones for people being mechanical (or kinetic), chemical, heat (or thermal) and radiant.

The problem for us is to get energy in a useful form in the right place and the right time for whatever we might wish to do.

We do this by means of converters, which change energy from one form to another, making it easier to store, transport, or use for work.

Human beings, for instance, are about 18% efficient. For every 100 calories we eat as food (chemical energy), only about 18 are turned into mechanical energy. The rest are lost for practical purposes, mostly as heat. Horses’ efficiency is only about 10%.

Agriculture allowed people greater control over the plant converters we call food crops.

Shifting agriculture probably increased energy availability 10-fold over that available through hunting and gathering and settled agriculture another 10-fold.

This translated into greater population densities. Then, as big animals were domesticated, people acquired more muscle power, more mechanical energy, in more concentrated form. Oxen for haulage and horses or camels for transport marked great improvements.

Since people are more efficient than horses and far better than oxen as converters of chemical into mechanical energy, big domesticated animals were something of a luxury in preindustrial times.

Slavery was the most efficient means by which the ambitious and powerful could become richer and more powerful. Curiously enough, it was fundamentally the answer to energy shortage.

In a burst of effort, the human body can muster 100 watts of power.

The most any society could devote to a given task, say ditch digging, dam building, or fighting, was — with people and animals as the main sources of mechanical power — a few hundred thousand watts.

The Ming emperors and Egyptian pharaohs had no more power available to them than does a single modern bulldozer operator or tank captain.

Expanding their territorial domain might increase rulers’ total energy supply. But even if that was a goal they pursued vigorously, it could not raise the total that they could apply to a single task.

For logistical reasons, it was usually impossible to concentrate more than a few thousand bodies on a given construction project or battle.

From ancient times forward, notably in Persia, China and Europe, windmills and watermills added slightly to the energy supply of agrarian societies.

Incremental improvements followed for many centuries. But in the 18th century, steam engines tapped hundreds of millions of years’ worth of photosynthesis, burning coal to convert chemical into mechanical energy.

Coal of course had found uses for centuries, mainly as a fuel for heating. But the steam engine’s capacity to convert that heat into mechanical energy capable of doing work opened up new possibilities.

The first steam engines were notoriously inefficient, losing more than 99% of their energy. But by 1800, gradual improvements allowed efficiency of about 5% and a capacity of 20 kilowatts of power in a single engine, the equivalent of 200 men.

By 1900, engineers had learned how to handle high-pressure steam, and engines became 30 times as powerful as those of 1800. On top of this, steam engines — unlike watermills and windmills — could be put anywhere, even on ships and railroad locomotives.

This created another positive feedback loop, in that it allowed transport of coal on a massive scale, providing the fuel for yet more steam engines.

19th century industrialization rested on this fact. World coal production, about 10 million tons in 1800, shot up 100-fold by 1900.

The worldwide energy harvest increased about fivefold in the 19th century under the impact of steam and coal. In the 20th century, it rose by another 16-fold with oil, and (after 1950) natural gas and, less importantly, nuclear power.

No other century — no millennium — in human history can compare with the 20th for its growth in energy use. We have probably deployed more energy since 1900 than in all of human history before 1900.

Very rough calculations suggest that the world in the 20th century used 10 times as much energy as in the thousand years before 1900 A.D. In the 100 centuries between the dawn of agriculture and 1900, people used only about two-thirds as much energy as in the 20th century.

Even on a per-capita basis energy use grew spectacularly, four- or fivefold in the 20th century.

In the 1990s, the average global citizen (an abstraction of limited utility) deployed about 20 “energy slaves,” meaning 20 human equivalents working 24 hours a day, 365 days a year.

The economic growth of the last two centuries, and the population growth too, would have been quite impossible within the confines of solely muscular energy.

But this energy intensification came at a cost. The average American in the 1990s used 50 to 100 times as much energy as the average Bangladeshi and directed upwards of 75 “energy slaves” — while the Bangladeshi still had less than one.

Harnessing fossil fuels played a central (though not exclusive) role in widening the international wealth and power differential so conspicuous in modern history.

This is a good thing if one prefers to see some people comfortable instead of almost all locked in poverty, but it is a bad thing if one prefers equality. In any case, inequality in energy use peaked in the 1960s. Thereafter, the transition to intensive energy use has begun to spread around the world.