Denmark shows how to cut emissions

Everyone seems to be talking about a carbon tax. It is probably the most glamorous - and certainly the most unlikely - use of the tax code since Al Capone got caught for tax evasion.

The idea is that polluters should pay for the environmental damage they cause. Slap a tax on carbon, the theory goes, and you will get fewer carbon emissions, more revenue for government and energy independence, all at the same time. No wonder people from both sides of the political divide have come out in support of it.

But a carbon tax is not a new idea. Denmark, Finland, Norway and Sweden have had carbon taxes in place since the 1990s, but the tax has not led to large declines in emissions in most of these countries - in the case of Norway, emissions have actually increased by 43 percent per capita.