IPCC confirms Six Degrees conclusions 16 May 07

It's always nice when real scientists come to the same conclusions as us amateurs. So I got a pleasant surprise, when flicking through the Summary for Policymakers of the IPCC's WGIII report, to see a table on page 23 which strongly resembles a table in the final chapter of Six Degrees, outlining the likely temperature rise associated with each incremental rise in CO2 concentrations.

Most importantly, this WGIII report concludes that to keep temperatures from crossing the all-important two-degree line global emissions must peak within the next 8 years – exactly the message I was trying to get across in the book. In fact, the situation may even be slightly more pessimistic than I allowed for, given that the year at which global emissions need to peak in this scenario is somewhere between 2000 and 2015.

As always there are various layers of complication here – the first is that the IPCC table is talking about temperature change at equilibrium: that’s the bit where the graph flattens out sometime around the year 2300. Most of the initial temperature rise would still take place this century, but they’re not quite the same thing – and that gives us some wriggle room. The second is, as I discussed in the book, that the two degrees target is about temperature change above pre-industrial levels – so 2C thereby equates to about 1.4C above 1990 levels, which is the scale I use (drawing on the 2001 IPCC Third Assessment Report temperature projections). That still counts as my ‘two degree world’, however, because I am talking about temperatures up to each degree in each case. In other words, the ‘six degree world’ is 5.1C to 5.8C, and so on down the scale.

Anyway, I hope this has been useful – I just get the feeling often when doing talks and lectures that the audience don’t quite believe me, because I’m frequently stating things in blunter terms than most scientists do. I’m now adding that Fourth Assessment Report table to my PowerPoint presentation – so that people can get the news straight from the horse’s mouth…