THE simplest advertising trick is the non sequitur. Promoting something dull like banking? Use comedy. Selling junk food? Use sexy actors. Wanting to raise awareness of a complex issue? Employ a celebrity.

We celebrate celebrities – until we realise that they’re no humbler than the rest of us, and then the secateurs come out. Take Cate Blanchett, who turns out to have an opinion, alongside 90 per cent of the population, about climate change and how to respond. Blanchett is starring, free of charge, in an advertisement supporting a carbon tax, part of an estimated $1 million campaign cobbled together by groups such as Greenpeace, GetUp! and the ACTU…