 So what images, Nick, spring to mind when you consider the world's most polluting industries? There's gas guzzling air travel. Shipping's got a pretty whopping carbon footprint, too. You might be forgiven for not thinking immediately. And Nick, I don't mean this to sound too indelicate for the first programme of our shift, flatulent farmyard animals. But the Danes, at least, are stealing a march on methane. The Copenhagen government is on a mission to drastically slash emissions. And their strategy? Well, it's tax.