I was explaning to the Multi-Party Climate Change Committee early in 2011 how I had worked out the costs and benefits of reducing emissions for the 2008 Review. The costs of reducing emissions will come straightaway. The benefits of reducing damage from climate change will come later—many of them to later generations of Australians. In fact there will be more and more benefits for later and later generations. So I needed a way of comparing the value of income to Australians who are alive right now with incomes of young Australians later in their lives and Australians who are not yet born.

‘So we had to choose the right discount rate’, I said. ‘We can't use the discount rates that determine values in the share market, because they take into account risks of a kind that are not relevant here.’

I got the feeling that the mention of discount rates had set Prime Minister Gillard's mind towards what she would say to Hillary Clinton about Afghanistan, Bob Brown's to the grandeur of the Styx Valley, and Tony Windsor's to the good rain that was falling on the Northern Tablelands.

But then I said something that brought back the prime minister's attention.

‘If we used the share market's discount rate to value the lives of future Australians’, I said, ‘and if we knew that doing something would give lots of benefits now but would cause the extinction of our species in half a century, the calculations would tell us to do it.’