Hansen's AGU Lecture

James Hansen's Bjerknes Lecture at the recent AGU meeting is well-worth reading -- it's thought-provoking and I learned a lot.

For example:

• it's simply a good review of the state of much of today's climate science
• clearly shows the effects of this past year's relatively strong La Nina
• shows ice age climate forcings and, from that, calculates a climate sensitivity of 3/4 C per W/m2, or 3 C for 2xCO2 and says he's "nailed it". (On his blog, Anthony Watts criticizes this but gets it completely wrong, thinking that Hansen used Mann data of the last 1400 yrs when, in fact, he uses ice-agey data of the last 20 Kyr.)
  
• gives lots of pretty charts neatly summarizing lots of data.
• shows a new method of calculating recent past and future climate, based on response functions, that is 100 trillion times faster than computer climate models. (This calculation actually shows a relative flattening of global temps for the first decade of this century, then resumed warming.)
• says he believes that our climate will "possibly" runaway if we burn all our coal and with runaway with "dead certainty" if we burn all coal + tars.
• repeats that our target goal for CO2 needs to be 350 ppm.

and lots more. I understood many of Hansen's points better than I did last May when I said I thought his "Target atmospheric CO2" paper had a lot of hand-waving arguments. (This paper has since been published in Open Atmos Sci J (2008) v2 p 217. You can download it here.) I mean, it's not the kind of rigorous calculation that physicists like, but it depends on a far smaller chain of hand-waving reasoning than I thought. But what do I know?

Anyway, it's worth an hour of your time.