Though of course I havent read the whole thing or anywhere close. I wonder if anyone ever will. Maybe it will be fun reading for Christmas! Or maybe not…
Looking at Part I. First science nugget: “a doubling of pre-industrial levels of greenhouse gases is very likely to commit the Earth to a rise of between 2 – 5Â°C in global mean temperatures.” Hmmm – where does that come from? 1.5-4.5 is the conventional range, has Stern rounded it up? Or is that IPCC 2007? And “Several new studies suggest up to a 20% chance that warming could be greater than 5Â°C.” – hmmm, sounds like James stuff. Perhaps I should admit my biases and say that I find James’s analysis quite convincing… maybe its just his forceful personality.
Before I get back to that, I notice “If the Greenland or West Antarctic Ice Sheets began to melt irreversibly, the rate of sea level rise could more than double, committing the world to an eventual sea level rise of 5 – 12 m over several centuries.”. Errrm… centuries? Current SRL is 2-3 mm/yr, ie 20-30 cm/century. Double that to 40-60 and you’re a fair few centuries into the future before you hit 5m, let alone 12. SRL is the “great white hope” of impacts, since its unequivocally bad (at least I’ve never seen anyone assert it to be a good). 5m is SRL in a millenium might well cause problems, true, but I’m not really happy looking that far ahead – tech could do anything by then.
Back to the sensitivity… scroll down to page 9, box 1.2. Which includes “Some studies, e.g. Annan & Hargreaves (2006), have used statistical techniques to estimate climate sensitivity through combining several observational datasets (such as the 20th century warming, cooling following volcanic eruptions, warming after last glacial maximum).” Errm, but doesn’t point out that A+H gives a low prob to anything over 5 oC. I’m not sure where all the other lines on the graph come from, or whether they should be considered reliable or not. Clearly, only a few of them give any kind of probability to > 5 oC.
And if you get down to table 1.1 (page 12) the range of T is enormous. The problem here is the same one that has been around for ages: there is a large range of plausible temperatures and you can slate your language how you like to get emphasise different estimates. The trick is to find some sensible way of weighting the different estimates to say something useful. If Stern has managed to do that, I haven’t got that far yet – maybe its in part II. My initial impression, especially from box 1, is that Stern is putting the weight of his words onto the high-end scenarios, and I’m not sure this is justifiable from a neutral point of view.