Critics of the U.S. tax system argue that it harms incentives to work, save, and innovate and therefore reduces long-run economic growth. Can you see why "green taxes" might promote economic efficiency and economic growth? Consider, for example, taxes on sulfur or carbon-dioxide emissions or on leaky oil tankers. Construct a list of taxes that you think would increase efficiency, and compare their effects with the effects of taxes on labor or capital income.