Extrasomatic: outside of the body
About 10 millennia ago… the first patches of deliberately cultivated plants as a small share of the Earth’s total photosynthesis becomes controlled and manipulated by humans who domesticate—select, plant, tend, and harvest—crops for their (delayed) benefit. The first domestication of animals soon follows. Before that happens, human muscles are the only prime movers—that is, converters of chemical (food) energy to the kinetic (mechanical) energy of labor.
Domestication of working animals, starting with cattle some 9,000 years ago, supplies the first extrasomatic energy other than that of human muscles—they are used for field work, for lifting water from wells, for pulling or carrying loads, and for providing personal transportation. And much later come the first inanimate prime movers: sails, more than five millennia ago; waterwheels, more than two millennia ago; and windmills, more than a thousand years ago.
… [for] century after century, there is just repetition, stagnation, or the slow growth and diffusion of these long-established conversions. In the Americas and in Australia (lacking any draft animals and any simple mechanical prime movers), all work before the arrival of Europeans is done by human muscles. In some of the Old World’s preindustrial regions, harnessed animals, wind and running or falling water energize significant shares of grain milling, oil pressing, grinding, and forging, and draft animals become indispensable for heavy field work (plowing above all, as harvesting is still done manually), transporting goods, and waging wars. But at this point, even in societies with domesticated animals and mechanical prime movers, much of the work is still done by people.
My estimate, using necessarily approximate past totals of working animals and people and assuming typical daily work rates based on modern measurements of physical exertion, is that — be it at the beginning of the second millennium of the Common Era or 500 years later (in 1500, at the beginning of the early modern era) — more than 90 percent of all useful mechanical energy was provided by animate power, roughly split between people and animals, while all thermal energy came from the combustion of plant fuels (mostly wood and charcoal, but also straw and dried dung).
And then in 1600… [we observe] something unprecedented. Rather than relying solely on wood, an island society is increasingly burning coal, a fuel produced by photosynthesis tens or hundreds of millions of years ago and fossilized by heat and pressure during its long underground storage. The best reconstructions show that coal as a heat source in England surpasses the use of biomass fuels around 1620 (perhaps even earlier); by 1650 the burning of fossil carbon supplies two-thirds of all heat; and the share reaches 75 percent by 1700.
England has an exceptionally early start: all the coalfields that make the UK the world’s leading 19th-century economy are already producing coal before 1640. And then, at the very beginning of the 18th century, some English mines begin to rely on steam engines, the first inanimate prime movers powered by the combustion of fossil fuel. These early engines are so inefficient that they can be deployed only in mines where the fuel supply is readily available and does not require any transportation. But for generations the UK remains the most interesting nation [in terms of energy use]… because it is an exceptional early adopter.
Even by 1800, the combined coal extraction in a few European countries and the United States is a small fraction of British production. By 1800… across the planet, plant fuels still supply more than 98 percent of all heat and light used… and human and animal muscles still provide more than 90 percent of all mechanical energy needed in farming, construction, and manufacturing. In the UK, where James Watt introduced an improved steam engine during the 1770s, the Boulton & Watt company begin to build engines whose average power is equal to that of 25 strong horses, but by 1800 they have sold less than 500 of these machines, merely denting the total power provided by harnessed horses and hard-working laborers.
Even by 1850, rising coal extraction in Europe and North America supplies no more than 7 percent of all fuel energy, nearly half of all useful kinetic energy comes from draft animals, about 40 percent from human muscles, and just 15 percent from the three inanimate prime movers: waterwheels, windmills, and the slowly spreading steam engines. The world of 1850 is much more akin to the world of 1700 or even of 1600 than that of the year 2000.
But by 1900 the global share of both fossil and renewable fuels and of prime movers shifts considerably as modern energy sources (coal and some crude oil) provide half of all primary energy, and traditional fuels (wood, charcoal, straw) the other half. Water turbines in hydro stations generate the first primary electricity during the 1880s; later comes geothermal electricity, and after the Second World War nuclear, solar, and wind electricity (the new renewables). But by 2020 more than half of the world’s electricity will still be generated by the combustion of fossil fuels, mainly coal and natural gas.
By 1900, inanimate prime movers supply about half of all mechanical energy: coal-fired steam engines make the greatest contribution, followed by better-designed waterwheels and new water turbines (first introduced during the 1830s), windmills and brand-new steam turbines (since the late 1880s), and internal combustion engines (gasoline-fueled, also first introduced in the 1880s).
By 1950, fossil fuels supply nearly three-quarters of primary energy (still dominated by coal), and inanimate prime movers—now with gasoline- and diesel-fueled internal combustion engines in the lead—provide more than 80 percent of all mechanical energy.
And by the year 2000 only poor people in low-income countries depend on biomass fuels, with wood and straw providing only about 12 percent of the world’s primary energy. Animate prime movers hold only a 5 percent share of mechanical energy, as human exertions and the work of draft animals are almost completely displaced by machines fueled by liquids or by electric motors.
During the past two centuries… [we have] witnessed a rapid global substitution of primary energy sources, accompanied by the expansion and diversification of fossil energy supply, and the no less rapid introduction, adoption, and growth in capacity of new inanimate prime movers—first coal-fired steam engines, then internal combustion engines (piston and turbines). [We now] see a truly global society built and defined by mass-scale, stationary, and mobile conversions of fossil carbon, deployed everywhere but in some of the planet’s uninhabited regions.
Vaclav Smil – How the World Really Works: The Science Behind How We Got Here and Where We’re Going [amazon link]