Emissions trading markets can help cut pollution effectively and affordably. The researchers analyzed the EU Emission Trading Scheme (ETS) and found that some designs may not always meet their pollution reduction goals. In the EU-ETS, setting emission caps can lead to too many pollution permits, discouraging companies from lowering emissions and making big profits. By using math models, the researchers showed that better-designed pollution trading systems can hit emission targets at a lower cost and promote clean technologies, like in a hypothetical plan for the Japanese electricity market.