Cap and Trade Game: How Cap and Trade Works, Hands-On

Cap and trade is much easier to understand once you run one. Prometheus lets you simulate a cap and trade market so you can see how a cap, tradable allowances, and a market price fit together, instead of just reading the definition.

What is cap and trade?

Cap and trade is a way to cut emissions by putting a firm limit, the cap, on the total emissions allowed across the covered sectors. The regulator issues a fixed number of tradable allowances that add up to the cap, where each allowance usually represents one tonne of carbon dioxide. Companies must hold enough allowances to cover their emissions, and they can buy and sell allowances with each other. The cap is lowered over time to drive emissions down.

How does cap and trade work in practice?

Because the supply of allowances is fixed by the cap, a price emerges from supply and demand. A company that can cut its emissions cheaply will do so and sell its spare allowances for a profit. A company that would find cutting expensive will instead buy allowances, as long as the price is lower than the cost of upgrading its own operations. That is the core idea: emissions get cut wherever it is cheapest, and the market price guides where that happens.

Why simulate cap and trade?

The behaviour of a cap and trade market is hard to follow on paper, because the price reacts to every firm's choices at once. A simulation lets you watch it happen: the price rising as the cap tightens and allowances get scarce, firms weighing whether to abate or buy, and the squeeze of a compliance deadline. Running it yourself turns an abstract policy into something you can feel.

How the Prometheus cap and trade simulation works

In Prometheus you take on a firm that must cover its emissions with allowances. You decide whether to cut emissions using your abatement options or to buy allowances from the market, you trade against AI-driven firms with different strategies, and you face a compliance deadline with a penalty for falling short. Prometheus can model both cap and trade (absolute) markets and intensity-based markets, so you can also compare how the two designs behave.

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Frequently asked questions

Is there a free cap and trade game? Yes. Prometheus is a free, browser-based simulation of a cap and trade market.

What is the difference between cap and trade and a carbon tax? Cap and trade fixes the quantity of emissions through the cap and lets the market set the price. A carbon tax fixes the price and lets the quantity adjust. Cap and trade gives certainty on emissions; a tax gives certainty on price.

How does cap and trade lower emissions? The cap is reduced over time, shrinking the supply of allowances, which raises the price and pushes firms to cut emissions where it is cheapest.

Can I use it to teach cap and trade? Yes. It works as a hands-on classroom or workshop exercise. For a guided session, email hipromets@gmail.com.