The U.S. system is not achieving greenhouse gas emissions reductions, so it would be comparing apples and oranges. The U.S. system is producing reductions in sulphur dioxide emissions. Carbon taxes are obviously reducing different pollutants. I think it is important to look at the European experience and the emissions trading system that was put into place across the European Union.
The first point is that these two tools can be used at the same time within a nation, so the European nations that have carbon taxes are also participating in the European cap and trade system--