The researchers studied different fuel policies to see how they affect people and the environment. They looked at the effects of the Renewable Fuel Standard (RFS), Low Carbon Fuel Standard (LCFS), and a carbon tax on biofuels and greenhouse gas emissions. The RFS encourages using biofuels made from food crops, which lowers fossil fuel use but raises food prices and doesn't reduce global emissions much. The LCFS and carbon tax are better at cutting emissions. Overall, the US benefits from these policies, even without considering the environment. However, globally, only the carbon tax helps increase social welfare, while the RFS and LCFS can hurt it due to their costs.