The fossil-fuel revolution: Fossil-fuelled civilisation today

5.1 Fossil fuels still supply about 87% of the world's primary energy

The Energy Institute's Statistical Review of World Energy 2025 puts the world's total energy supply in 2024 at a record of about 592 EJ. Oil provided about 199 EJ, coal about 165 EJ and natural gas about 149 EJ: roughly 513 EJ together, or 86.6% (calculated; the review rounds it to 87%). Every fossil fuel grew in 2024, and so did total demand, by around 2%.

The headline share looks higher than the figure of about 80% that was often quoted a few years ago. Part of the difference is accounting. The 2025 edition dropped the old substitution method, which counted non-fossil electricity as the fuel a thermal plant would have burned to make it, and adopted a physical energy content method. That credits nuclear, hydro, wind and solar with less energy and so lifts the fossil share. The physical reality has not changed much: wind and solar are growing fast, up 16% in 2024, but from a small base, and fossil use is still rising in absolute terms.

Oil remains the largest single source, with world demand passing 101 million barrels a day for the first time in 2024. Coal set a new record; China burned about 56% of it (calculated from the review's tables). Natural gas returned to growth. Coal-fired plants generated about 10,600 TWh, still the largest source of electricity in the world.

This is the clearest illustration of Smil's point about transitions. After decades of policy effort and rapid growth in renewables, the share of fossil fuels in world energy has moved by only a few percentage points. The absolute amount of fossil fuel burned is the highest ever, and the 2026 edition, covering 2025, put total supply above 600 EJ with fossil fuels still at about 86%.

• Energy Institute (2025). Statistical Review of World Energy 2025, 74th edition (2024 data). London: Energy Institute. web ↗ · web
• Energy Institute (2026). Statistical Review of World Energy 2026, 75th edition, summary version (2025 data). web ↗ · web
• Smil, How the World Really Works (2022) · via Smil Mastery Course, M5 'Fossil-fuelled civilization'

5.2 Each of us commands dozens of energy servants

One way to grasp what fossil fuels did is to translate energy into human labour. A healthy adult doing steady physical work can sustain about 100 watts of useful output over a working day. Smil, in How the World Really Works, divides the world's total useful energy by that human rate. The result is that the average person on Earth now has the equivalent of about 60 adults working for them without rest. In rich countries the figure is several hundred.

These energy servants plough and fertilise the fields, pump water, smelt metals, bake cement, drive trucks and ships, fly aircraft, light homes and run computers. No ancient emperor with thousands of slaves commanded the mobility, light, food variety and comfort that an ordinary family in a rich country takes for granted, and almost all of it rests on fossil fuels.

The servants are, however, very unequally distributed. Rich countries use roughly 150 to 300 GJ of primary energy per person per year. Many low-income countries use less than 20 GJ. India, despite rapid growth, still uses well under half the world average of about 73 GJ per person (592 EJ shared among about 8.1 billion people, calculated). Smil shows that measures of welfare such as life expectancy, infant survival and schooling rise steeply as energy use climbs from very low levels, then level off well below rich-world consumption.

That pattern sets the central dilemma. Billions of people still need more energy services, while the world must cut the emissions those services have historically produced.

• Smil, How the World Really Works (2022) · via Smil Mastery Course, M5 'Fossil-fuelled civilization'
• Smil, Energy in Nature and Society: General Energetics of Complex Systems (2008) · via Smil Mastery Course, M5 'Fossil-fuelled civilization'

5.3 The benefits came with costs that are now global

Fossil energy always had a price beyond the money paid for it. Early coal mining was dangerous, with frequent explosions, roof falls and long-term lung disease, and it used child labour. Coal smoke darkened industrial cities and killed many people through respiratory illness; London's smog of 1952 was only the most famous episode. Burning sulfur-rich coal and oil caused acid deposition that damaged lakes and forests in Europe and North America, until scrubbers and cleaner fuels brought it under control.

The largest burden is carbon dioxide. Every tonne of coal burned releases roughly 2.5 tonnes of CO₂, every tonne of oil about 3.1 tonnes, and every tonne of natural gas about 2.7 tonnes. Energy-related emissions reached a record of about 40.8 billion tonnes of CO₂ equivalent in 2024, according to the Energy Institute. The accumulation of this gas in the atmosphere is the main driver of climate change, which is why the world is attempting a new energy transition.

Smil's history explains why that transition is hard. Fossil fuels are dense, storable and cheap to transport. They are embedded in four material pillars of modern life: steel, cement, plastics and ammonia. The equipment that uses them, from blast furnaces to ships, lasts decades. Earlier transitions, from wood to coal and from coal to oil, each took half a century or more, and they added a better fuel rather than removing an incumbent one. The coming change must do the reverse, at a larger scale, and faster. Understanding how the fossil revolution happened is the starting point for judging how quickly it can be undone.

• Smil, How the World Really Works (2022) · via Smil Mastery Course, M5 'Fossil-fuelled civilization'
• Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M5 'Coal and the great transition'
• Energy Institute (2025). Statistical Review of World Energy 2025, 74th edition (2024 data). London: Energy Institute. web ↗ · web

See it in the table

Check your understanding

According to the Energy Institute's 2025 review, what share of world primary energy came from fossil fuels in 2024?

Why does the 2025 fossil share look higher than the roughly 80% often quoted earlier?

Smil's energy-servant calculation shows the average person on Earth commands the equivalent of about how many adults working nonstop?