The Clean Air Act is important for US climate policy and regulates greenhouse gas emissions from coal power plants. A study looked at different ways to reduce these emissions and found that increasing coal prices can improve efficiency. A 10% increase in coal prices leads to a 0.1%–0.4% efficiency improvement. This means that power plants produce more electricity per ton of coal. The study also showed that higher coal prices affect how much coal power plants are used. Comparing different policies, the study found that performance standards are not as efficient as a tax for reducing greenhouse gas emissions from coal plants.