Cobra Effect · Incentives and systems
The Jevons paradox
Why making something efficient can make us use more of it.
6 cards, read aloud in 2:31, with a test and sources.
England, 1865. A young economist worries that the coal will run out.
William Stanley Jevons is not yet 30 and writing a book called The Coal Question. Britain runs on coal, and the seams will not last forever. The obvious answer is to burn it more carefully. Jevons says that is exactly backwards.
Watt’s engine burned far less coal per job. So Britain burned more coal.
James Watt’s steam engine got much more work from each ton of coal than the engines before it. So steam became cheap. Cheap steam went into mills, mines, railways and ships that would never have been built at the old price. Britain burned more coal than ever.
That is the Jevons paradox.
Make something more efficient and you make it cheaper to use. Cheaper things get used more, and in new ways nobody planned. If the new uses grow faster than the savings, total consumption goes up. Jevons put it plainly. It is a confusion of ideas to suppose that economical use of fuel means less of it gets used.
It has never gone away.
Economists now call the milder version the rebound effect. A more efficient car is cheaper per mile, so people drive further. Lighting is the famous case. Each new lamp, from candle to gas to electric, cost less per hour of light, and the world lit more and more. The saving is real. It just gets spent.
The trap for anyone who plans.
A council widens a road to cut congestion, and the cheaper journey draws new drivers. A firm gives staff a faster tool, and the work does not shrink. It multiplies. Efficiency does not decide how much of a thing gets used. Price does, and efficiency lowers the price.
So when someone promises a saving, ask where it will go.
If the goal is to use less of something, efficiency alone will not get you there. You need a cap, a price, or a limit that still holds when the thing gets cheap. Jevons was wrong about the coal running out. He was right about us.
Sources
- Jevons paradox, Wikipedia. The paradox, the quote from Jevons about the economy of fuel, and the argument about whether it holds for modern energy policy.
- The Coal Question, William Stanley Jevons, 1865. The original. A worried Victorian book about British coal, with the efficiency argument in the middle of it. The full text is free online and this page summarises it.
- Rebound effect, Wikipedia. The modern, milder form: how much of an efficiency saving gets eaten by extra use, and the studies that have tried to measure it.
Nearby ideas
- Second order effects. Every fix has consequences, and those have consequences too.
- The Cobra effect. Why paying for a result can breed more of the problem.
- Braess’s paradox. Why adding a road can make everyone’s journey slower.
- Path dependence. Why early choices stay locked in long after better ones appear.
- The Lindy effect. The longer an idea has lasted, the longer it is likely to last.
- Antifragility. Some things get stronger from knocks, and fail without them.
- The Streisand effect. Trying to hide something is often the best way to spread it.
- The principal-agent problem. When someone acts for you, their own interests quietly steer the work.