Green is clearly the "in" colour this season. In the US, Republican stalwarts such as John McCain, senator, and Ar-nold Schwarzenegger, governor, have been pushing measures to deal with climate change. In the UK, the left-of-centre Liberal Democrat party and the right-of-centre Conservatives claim green credentials. Each has been arguing for an increase in environmental taxes, designed to discourage air travel or the purchase of gas-guzzling cars.

Green taxes have been praised in some quarters as a pain-free way to help the planet and the economy at the same time. They have also been criticised as a crude revenue-grab. Both views are simplistic.