How did we come to depend so much on fossil fuels?

This is another post inspired by my current first year physics course, The Physics of Sustainable Energy (PHY123).

Each inhabitant of the UK is responsible for consuming, on average, the energy equivalent of 3.36 tonnes of oil every year. 88% of this energy is in the form of fossil fuels (about 35% each for gas and oil, and the rest in coal). This dependence on fossil fuels is something new; premodern economies were powered entirely by the sun. Heat came from firewood, which stores the solar energy collected by photosynthesis for at most a few seasons. Work was done by humans themselves, again using energy that ultimately comes from plant foods, or by draught animals. The transition from traditional, solar powered economies, to modern fossil fuel powered economies, was sudden in historical terms – it was probably not until the late 19th century that fossil fuels overtook biomass as the world’s biggest source of energy. The story of how we came to depend on fossil fuels is essentially the story of how modernity developed.

The relatively late date of the world’s transition to a fossil fuel based energy economy doesn’t mean that there were no innovations in the way energy was used in premodern times. On the contrary, the run-up to the industrial revolution saw a series of developments that greatly increased the accessibility of energy. A combination of selective animal breeding and better technology for harnessing those animals saw the power available from draft animals increase from the 300 W or so of ploughing power that prehistoric farmers might have got from each of their yoked oxen, to the 800 W or so that an early modern farmer could expect from a single Shire horse with a collar harness. From the middle east and China came increasingly efficient water wheels delivering multiple kW, while from the 12 century or so windmills delivering similar amounts of power became increasingly common across Europe. These mills delivered concentrated power for a variety of industrial processes beyond the corn-milling with which they are most associated, for example fulling cloth, and powering bellows for blast-furnaces and hammers for iron-working. Nonetheless, it is likely that human labour remained the dominant source of mechanical energy until the 19th century.

Coal was already being mined in England in medieval times, initially as a local substitute for firewood. A rapid take-off in the use of coal began in the 16th century, driven by the development of long-distance trade (especially by coastal freighters from the North East to London). It is estimated that in England by 1650 coal had already surpassed firewood as a source of energy. If in the first phase of coal use, coal replaced firewood for domestic heating, a second phase involved the use of coal for energy intensive industrial processes. Possibly the first industrial use to take off was the use of coal to make malt for beer, but by far the most famous was the development of a process for large-scale iron-making using coke rather than charcoal, as developed by Abraham Darby in Coalbrookdale in the early 18th century.

What was driving this substitution of coal for biomass? The real scarcity at this point was not so much energy, as land. It wasn’t that early modern industrialists were cutting down virgin forests for firewood – there were already well-developed methods for managing woodlands to sustainably harvest biomass for charcoal. A well managed system of coppiced hardwoods would produce between 5 and 10 tonnes of wood per hectare sustainably, giving an energy yield of perhaps 75-150 GJ per hectare per year. But by 1850 England and Wales’s consumption of coal had already reached 1.7 million TJ. This amounts pretty much to the theoretical energy yield if the whole land area of England and Wales was devoted solely to growing firewood. Coal in effect released England from the constraint of its finite land area.

Meanwhile a third phase in the use of coal was getting going, based on the invention of the steam engine, allowing coal to substitute not just for other sources of heat, but for directed mechanical energy. The earliest versions of steam engines, as introduced by Newcomen in the early 18th century, were hugely inefficient. That meant that their major early use was for pumping water out of coal mines, where the cost of fuel was less important. The first uses of coal to do mechanical work, then, were to help mine more coal. Improvements in efficiency continued throughout the 18th century, but Watt’s invention of the separate condenser was a significant breakthrough opening up the way for much more widespread use of steam engines in industry.

Mass production and the factory system had begun in the UK before Watt’s improvements to the steam engine, driven by water power. But the 19th century saw a period of exponential improvement in the efficiencies of steam engines – a sort of Victorian version of Moore’s law. Steam engines made it possible to site factories, not just where there was access to waterpower, but wherever was convenient, and of course it was smaller, lighter, more efficient steam engines that made the development of the railways possible. There’s no space here to go into all the other developments that created the modern world, and in particular the great technological saltation of the period 1867-1914, when a short space of time saw the introduction of steam turbines, widespread electrification, internal combustion engines, the car, and the aeroplane. All of these technologies depend on the large-scale availability of fossil fuels, so our dependence on these technologies has in turn locked us into dependence on those fossil fuels.

It was at the end of this period that possibly the most significant innovation of all took place. The German chemist Fritz Haber developed a process for synthesising ammonia from atmospheric nitrogen, and Carl Bosch, supported by colossal sums of German government money, converted this into a large scale industrial process driven by fossil fuel energy. It was the widespread availability of artificial nitrogen fertilisers made by the Haber-Bosch process that drove the large increases in crop yields of the twentieth century, which in turn has permitted the 20th century growth in world population. In Vaclav Smil’s estimation, well over half the world’s current population depends on the Haber-Bosch process for their very existence.

So what have the consequences been of this massive shift to a dependency on fossil fuels? Increased energy use has led to increased material prosperity, and there are strong correlations between access to energy and a wider variety of measures of well-being. As time goes on, our use of energy has become more efficient in the sense that the amount of energy required to produce a £ of GDP has fallen. But GDP has risen faster than energy efficiency, so total energy use per capita goes on rising. But the other consequence of burning all that coal, oil and gas has been a very substantial rise in the carbon dioxide composition of the atmosphere, which has already changed the earth’s climate. The consequences of that continuing climate change are still uncertain, but the outlook should worry us.

That’s the dilemma we are now in; we depend on that 3 tonnes of oil a year for our prosperity and well-being, for our very existence. But we know things can’t continue this way for ever. We’ve become dependent on fossil fuels, and we need now to reverse that dependency. How to manage that transition remains our biggest challenge.

Sources: the most comprehensive and quantitative overviews come from the work of Vaclav Smil, in particular Energy in World History and Energy in Nature and Society . My data on the uptake of coal in the UK comes from E.A. Wrigley’s Energy and the English Industrial Revolution. Readers who find this discussion too anglocentric will enjoy Kenneth Pomeranz’s The Great Divergence, which offers some interesting observations about the puzzle that the take off of fossil-fuel based industrialisation took place in Northwest Europe, rather than China, despite the fact that China has ample coal supplies and, in 1700, was arguably more technologically advanced than northwest Europe.