âWe have been living in a fundamentally transformed world powered by fossil fuels for less than two centuries. The dependence now runs far deeper than most people realize.â â Vaclav Smil
Energy is not merely a sector of the economy. It is the universal currency of all physical processes, and the story of human civilization is, above all else, a story of energy. Every loaf of bread, every steel beam, every container ship crossing the Pacific, every data center running artificial intelligence - all of it is an act of energy conversion.
Smil opens How the World Really Works with a declaration that challenges contemporary discourse: before we can understand where we are going, we must honestly reckon with where we are and how we got here. And the honest answer is that we live in a world built almost entirely on fossil fuels - coal, oil, and natural gas - and that dependence is deeper, more pervasive, and more difficult to unwind than almost anyone in public life is willing to acknowledge.
In 2020, fossil fuels provided approximately 83% of the worldâs primary energy. Despite decades of investment in renewables and widespread declarations of green energy revolutions, that share has barely moved in 30 years. In 1990, fossil fuels provided about 86% of primary energy. The change has been modest.
To understand why this is so difficult to change, you have to understand what primary energy actually is. It includes not just electricity - which is what most people think of when they think of energy - but all the energy used in transportation, industrial heating, manufacturing, agriculture, and the production of materials. Electricity accounts for only about 20% of total final energy consumption in most countries.
The reason fossil fuels came to dominate the global economy is simple: energy density. A liter of diesel fuel contains roughly 10,000 watt-hours of energy. A kilogram of lithium-ion battery stores about 250 watt-hours. The gap is a factor of 40 to 1.
This density advantage explains why ships run on diesel, why aviation relies on jet fuel, and why steel mills burn coal. Replacing these energy sources with lower-density alternatives is not simply a matter of political will or investment - it requires solving immense physical and engineering challenges.
Smil is the worldâs foremost scholar of energy transitions, and his most important lesson is that they take much longer than people assume.
The transition from wood and biomass to coal as the primary energy source took roughly 100 years in Britain, the most advanced industrial economy of the 19th century. The transition from coal to oil took another 50-70 years globally. These transitions happened when the new energy source was simply better and cheaper in every way.
The common narrative: We can transition to clean energy within 10-20 years if we simply have the political will and make sufficient investment.
The quantitative reality: The current global energy infrastructure - power plants, refineries, pipelines, ships, factories - represents tens of trillions of dollars of capital investment. Much of it has decades of useful life remaining. The sheer physical scale of what must be replaced is staggering: in 2020, the world consumed about 580 exajoules of primary energy. Wind and solar currently provide about 5% of that. Even with rapid growth, replacing the remaining 95% is a multi-decade undertaking.
One of Smilâs most powerful contributions is making visible the enormous quantities of energy embedded in ordinary products and processes.
The critical insight: when people speak of âelectrifyingâ the economy and powering it with renewables, they are addressing only a fraction of total energy consumption. The hard-to-electrify sectors - industrial heat, shipping, aviation, steel and cement production - are enormous, and their solutions remain elusive.
Smil insists on what he calls âquantitative literacyâ - the ability to reason with numbers rather than simply with narratives. The difference between a megawatt and a gigawatt is a thousandfold. The difference between a gigajoule and an exajoule is a billionfold. These are not trivial distinctions: they determine what is actually possible.
Think about the last 24 hours of your life. How many energy conversions made that day possible - from the electricity in your home to the fuel in the trucks that delivered your food to the gas that heated your water? What would it actually take to power all of those conversions without fossil fuels?