Repent, for the end of the world is nigh. That is a warning one would expect to come from an evangelical preacher or an environmental doomsayer, not from a sober economist. Yet that is, in essence, what Sir Nicholas Stern, author of the British government’s new report on climate change, is saying. The tone may be sober, but the conclusion – act now before it is too late – is not.

Hitherto many economists, business-people and politicians, particularly in the US, have argued that, given both the uncertainties and the high costs of taking possibly unnecessary action, the best policy is to wait, see and, if necessary, adapt. The contribution of this report is to reverse that logic. It argues that, given these very same uncertainties and the relatively low costs of acting now, the best policy is action.