You need enough years to be able to draw any kind of real conclusions, which is why Europe is the best place to do this. It has had carbon taxes going back to the 1990s in five or six countries. I've put two studies in my materials because a picture is worth a thousand words. One of them looks at the six countries that brought in carbon taxes in the 1990s, and what it shows is that over a period of about 20 years, those countries, if you isolate just the effects of the tax shift and nothing else, reduced carbon emissions by anywhere from about 3% to 6%. Those are relatively low taxes. They also saw GDP gains—not big ones, but anywhere from zero to 1%, so frankly within the range of error of the models.
Second is the OECD study that compared, under the European system, firms that are covered with those that aren't covered. Again, the firms that were covered by the carbon price had 11% greater emission reductions, but you'd expect that. What it also found is that they outperformed the firms that were not covered in terms of revenue, investment, employment, and innovation. The same study found that there was almost no evidence of economic leakage, which means firms moving elsewhere for competitive reasons. Part of that is because you reinvest the revenues as a way of creating economic incentives to spur clean growth in your economy.
Even Australia, while it had its carbon tax in, actually did better than the OECD average in terms of economic growth, and did better in terms of reducing emissions than it had before and after the carbon tax. It may not have been a political success in Australia, but it was actually a good policy while it was in place. There's only two years of evidence.