LONDON -- The obvious route is not always the best one. Throughout Europe the governments and political parties, as well as the central European Union Commission in Brussels, are all vying with each other to prove who is the greenest. The simplest way of doing this is to produce ever more ambitious plans and targets for cutting carbon dioxide (CO2 emissions, which are widely believed to be the main cause of global warming.

And the obvious way of doing that would seem to be by putting a price on carbon emissions, by rationing out emission allocations (permits) to all and letting those who do not use them trade with those who want more than they have been allotted. That is what the Kyoto Protocol proposed, and a raft of schemes have since then been worked out to establish international carbon-emissions trading.

On paper it all looks very neat. Schemes have now been developed worldwide, including in Japan. The EU has now gone even further than Kyoto with its Emissions Trading Scheme, which is now being boosted with even more ambitious targets.