The Summerfield Lecture at this year's Cheltenham Festival of Literature was the most authoritative I've heard for many years. Nicholas Stern gave it, his delivery low-key, almost deadpan; his message dynamite.
He gave us the up to date scientific consensus: not small probabilities of something unpleasant because of climate change, but big probabilities of something catastrophic. "Business as usual" for the next 100 years means a 50% chance of the earth's temperature being higher than for 30 million years, and movement of peoples on a massive scale. "This is not a Black Swan event."
Lord Stern explained exactly what's needed to give ourselves an even chance of limiting temperature rise to something manageable: the target is an 80% cut in each inhabitant of Europe's carbon emissions by the time 40 years have elapsed.
We need to decarbonise electricity, and switch all transport to using electricity; we need to develop low-carbon technology in every sphere; and we need to halt deforestation. A new industrial revolution is required to achieve the low-carbon growth needed to overcome world poverty.
The lecturer was hopeful of a robust outcome of the conference at Copenhagen, seven weeks ahead, but negotiations were at a critical stage. "We have an agreement to lose."