IT’S DIFFICULT to have a cool-headed debate about global warming. At a psychological level, the sheer scale of the issue – global, long-term, complex, threatening – tends to induce either paralysing despair or wilful ignorance. It doesn’t help that many protagonists in the debate, whether environmental NGOs or climate sceptics, bring with them all too obvious ideological baggage. In the United States, indeed, the notion that impartial evidence might assist judgement has been almost entirely abandoned now that climate change has become embroiled in the culture wars between the new conservative movement and their Democratic opponents.

So, as Professor Ross Garnaut unveils the update to his landmark report on Australia’s role in eight tantalising instalments and the federal government purs a date on a price on carbon, it might be useful to take stock of where we are…