Examining the effects of a carbon tax alone on GHG emissions would provide a more precise estimation of policy effectiveness. Many governments model the effects of a carbon tax acting alone during the implementation phase of the tax. For example, in the United Kingdom, according to a modeling study by Cambridge Econometrics (2005), the Climate Change Levy would reduce energy demand by approximately 15% (12.8 million metric tons) in the commercial and public sectors by 2010 (Her Majesty’s Treasury 2008:101). However, determining the actual impact of a tax in isolation of other factors is often difficult, and most evaluations have not attempted to do so. Because of the lack of common evaluation practices, it is difficult to compare the effects of policies across jurisdictions. Table 6 summarizes evaluations of either carbon emissions levels or program effectiveness that jurisdictions have conducted to gauge the impact of carbon taxes. For example, Sweden’s emissions were reduced by almost 9% between 1990 and 2006, while in Denmark, per capita emissions were reduced by 15% between 1990 and 2005.