We know what has to happen to give us a fighting chance of avoiding catastrophe. We need carbon emissions in rich countries to be 40 per cent lower than they were in 1990 – by 2020. We can haggle with each other over how to get there but we can't haggle with atmospheric physics over the end-goal: the Earth's atmosphere has put this limit on what it can absorb, and we can respect it, or suffer.
Yet the first week of this summit is being dominated by the representatives of the rich countries trying to lace the deal with Enron-style accounting tricks that will give the impression of cuts, without the reality. It's essential to understand these shenanigans this week, so we can understand the reality of the deal that will be announced with great razzmatazz next week.