Call me an old grump but the SPM for the IPCC AR4 report wasn’t terribly exciting. Which was, perhaps no great surprise: having read the draft chapters, or at least skimmed them, it was clear that nothing revolutionary was going to appear. They throw in the phrase Warming of the climate system is unequivocal which is a nice sound-bite but was true for the TAR too. Climate sensitivity is likely to be within 2-4.5 oC, but since this is only a 66% statement its quite weak; though they do go on to diss > 4.5 oC a bit. And the attribution key text is:
Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations12. This is an advance since the TAR’s conclusion that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.
So our advance since the TAR is insertion of the word “very” ;-)? No, thats unfair. There has been a lot of science since then, but the basic view of humans causing climate change hasn’t really altered very much.
[CJR says in a comment Might be a good thing... too much change in the fundamentals would lead to cries of, "look - they keep changing their mind about what they think!". Quite true, and what I meant to say myself. I was feeling a bit grumpy this morning due to negative theta in my model runs :-(. What this (the SPM; not -ve T) confirms is that much of the fundamentals in the TAR and before were correct, and are just being refined. Wasn't there a famous quote from Michaelson about that...? -W]
[Update: a href="http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/001085follow_up_ipcc_and_.html">RP Jr is obliged to admit that it wasn't as exciting as thought it might be - serve him right for believing the press... -W]