There's a lot of disquiet about emissions trading in Europe right now - the world's biggest carbon market.

Clearly, not everyone buys into the idea that this price signal will deliver the intended consequence of pricing in cleaner or rather low carbon energy technologies. Yet any price signal - where before there was none - always influences behaviour. Perhaps the greatest challenge for the carbon markets is to price out much further into the future.

AEI readers may be interested to read my interview with Dr Richard Sandor, who invented carbon trading. In this he explains the scheme and expresses high hopes that if the system is designed effectively, this market could be worth trillions of dollars.