The argument has changed. Irreversibly. Science has long provided a compelling reason to act against global warming. The study authored by Sir Nicholas Stern, the former World Bank economist, has now added the vital economic rationale.

Not so long ago the debate about climate change was framed, carelessly, as one in which upfront economic costs had to be weighed against a distant and uncertain risk. How much of our present prosperity should we sacrifice against the possibility the planet might one day get too hot? This was always a false choice, but also one well suited to the timidity of politicians and the suspicion of voters. The Stern report debunks it.