Back in March, I posted about a general-cl-ch talk I gave at Cafe Scientifique. After that, a student at Hills Road Six Form College (err, for non-UK folk, thats pre-university) invited me to give the talk there, which I finally did today, to an audience of 18 people (16-years-old-ish, I guess, and 2 teachers) at the "physics club" lunch time talk series.
This time, instead of a 10 minute talk that burst at the seams into a 15 minute talk, it was the same set of slides expanded to about 30-40 mins and 10 mins questions. And I was delighted with the questions, because they were far better, more interested, more aware than those from 70+ of the general public.
And those questions were... some discussion of THC collapse, aka "Day after tomorrow". Its fairly clear people are still keen on it as a concept, no matter how much I try to downplay it. Q: "didn't it happen in the past, 13 kyr ago?" (internal answer: well done, right date, you don't get that often): A: yes, but linked to the Laurentide ice sheet, that mechanism can't happen now. Q: "but what about glaciers in the Urals etc? Is that in the GCM runs?" A: snow in the Urals may be in there but glaciers too small to represent in GCMs; but then the amount of water from those sources is probably too small.
I explicitly mention impacts/politics at the end (largely to say: not my job guv; and trade-offs), so some Qs on that: "do economists try to value the environment?" to why my A: yes, papers in Nature etc, but its hard to do in a way that anyone will agree on (and there are at least 2 types of value: direct-econ-benefits that may not have been counted (e.g. water catchments), and pleasure-value (hiking in the hills)). Also Q: "but do your scenarios count the emissions from rapidly-industrialising India/China, and should/can we stop them?" A: yes the pessimistic ones do (I show the SRES range from the TAR SPM, I think); and how we end up with a vaguely equitable distribution of GHG emissions I don't know; tech transfer perhaps; obviously they are likely to want our material standard of wealth, but hopefully they don't want all the crap we've got: I don't want to give up decent dentistry or doctors, but they are welcome to the M11.
Q: "what about uncertainty/surprises (I'd talked briefly about the W Ant ice sheet collapse as an unquantifiable possible effect): shouldn't they be factored into the political calcs?". A: yes, but its tricky to see how to do that. A sane system would: in our insane system the major GHG emitter won't even accept the clear and obvious science, let alone the unknown bit (its all right, I didn't say "insane").
Global dimming got asked about (a hang-over from Horizon): see RC for that, which I parrotted. "Committed change" too: yes, about 0.6 oC according to the most recent Hansen et al. (See RC again).
So, a good session overall. My "public outreach" for the day, or PUS as we call it here (Public Understanding of Science).