Comments 1 to 20:

1. dpovey at 18:15 PM on 7 May, 2010
   Really enjoyed your talk John, and yes it's a shame that the moderator let the panel waffle a bit and we missed the opportunity to see some skeptic smackdowns :-).
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2. quokka at 18:52 PM on 7 May, 2010
   Very nice set of slides with excellent logical progression. Lots of material to get through in 20 mins. The ABC science show Catalyst this week had an interesting piece on "CO2 is plant food". The point was essentially that even if higher CO2 is good for plants (disregarding issues of water, nutrients etc) it may not be good for either humans or the ecosystem as a whole. At high CO2 levels protein content of important crops drops significantly and levels of toxins in some plants increase significantly. One suggested consequence was that under such conditions Koalas may no longer be able to subsist on a diet of Eucalyptus leaves. (Maybe deniers can fixate on Koala bears instead of Polar bears now!) It would be interesting to know more about this research if anybody has any references.A guest post would be nice :)
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3. HumanityRules at 20:03 PM on 7 May, 2010
   That reminds me, Mark E. Smith of 'The Fall' famously used to sing through two mics at gigs, it never did him any good either. The Fall - "What about us?" "question time which was dominated by discussion of policy, human psychology and over-population" I enjoy the focus this website has on the science but it's worth remembering that it's the politics that really drives policies on climate change. Misanthropic ideas about human nature and population are the most worrying aspect of the whole affair to me.
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4. Ned at 21:38 PM on 7 May, 2010
   Congratulations, John. I'm going to download your slides and look them over. I wish I were able to go to one of your talks, but unfortunately I'm in the wrong hemisphere :-( John writes: [...] my notes (which I forgot to refer to on the day anyway) [...] Apart from a few hiccups [...] I had trouble fitting all the content into 20 minutes [...] I had to jettison [...] which was a great shame (I have much fondness for those graphics). Mental note: make sure I'm allocated enough time to include my superfluous but pretty graphics next time around. [...] Unfortunately, there was only time for a couple of questions which was a disappointment. [...] Well, I've given many dozens of scientific talks over the past couple of decades and the laments you list above could have described pretty much ... all of them! If those are the worst you can say in retrospect, consider it a great success. (No surprise to anyone here, we've seen ample evidence of what an effective communicator you are.) I hope you'll keep doing these presentations because they're desperately needed.
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   Response: Looking at all those quotes, I really am a glass-half-empty type! :-(
   
5. Ned at 22:41 PM on 7 May, 2010
   Okay, I've looked through your slides, and you've really done a good job of covering the main points. I like the fact that you include some graphics that are actually very fundamental but that aren't always shown in these kinds of talks. What would I add if you had more time? Maybe a slide or two about ocean acidification ... it's important to remind people about that, particularly since a lot of proposed geo-engineering "solutions" only address warming, not ocean pH. Also, depending on the audience, it might be nice to include positive examples of "citizen science" (e.g., people verifying the surface temperature trend by independently analyzing the same data used in the four "official" data sets [GISS, CRU, NCDC, JMA] ... yes, I know I've been obsessing about this lately; sorry, I just think what Clear Climate Code, etc. have done is really neat!) A slide about this would probably be appreciated by an audience of engineers or non-academics. What would I trim if you needed to save time? I don't know exactly how much time you spend on each section, but I note a string of 9 slides in the middle that focus on the cryosphere (starting with "glaciers are retreating" and ending with "Arctic sea ice is melting"). If you needed to shorten it up a bit, you might be able to consolidate this topic, though it'd be a shame to not include any of the figures you've got there. All in all, well done!
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   Response: I intentionally left out ocean acidification because the next talker, Ove, was a coral reef researcher with many peer-reviewed papers on the subject. I didn't want to steal his thunder. If I present that talk in the future, if I have more time, I would add more impacts at the end.
   
6. James Wight at 23:38 PM on 7 May, 2010
   A good summary of the basic science – though it is a shame you had to cut some slides. Have you thought have using the graph on slide 31 in a response to “Deserts are retreating”? Also, just out of interest, where did that temperature graph on slide 4 come from? It doesn’t look much like the usual “hockey team” of reconstructions.
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   Response: It's by Katharine Hayhoe, a climate scientist from Texas. It's constructed from ice core and sediment records, she kindly sent me the raw data so I was able to plot it in a format matching the other graphs. I used it because of its longevity, most of the other hockey stick graphs only go back 1000 to 2000 years.
   
7. Paul D at 00:47 AM on 8 May, 2010
   John I think a comment you make in your PDF notes is key to the skeptical attacks and strategy. You said: "...independent lines of evidence all point to the same result..." For those that understand the issues 'independent lines of evidence' are key to proving something. They are the fingerprints of the big picture. However those same 'independent lines of evidence' are a political gift for those that want to spread doubt and confusion.
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8. D Kelly O at 01:07 AM on 8 May, 2010
   John: Great slideshow, I'll add a link to it on my blog. Ned: I agree with your comment about ..."positive examples of "citizen science". Keep on "obsessing", you have at least 1 supporter!
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9. Byron Smith at 01:08 AM on 8 May, 2010
   Thanks John - another great resource! I second the comment above about including ocean acidification in any future and slightly longer presentations. Also, if you think you might start getting more invites to information sessions like this, a short course on public speaking might be useful. I have no idea of your skills in this area, and so don't take this as any kind of attack, but everyone can improve and if you've only done a few talks, then getting a handle on some of the basics could help your verbal communication. This message is too important to have people distracted by irrelevant factors.
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10. Alexandre at 01:10 AM on 8 May, 2010
    Very good slideshow. I downloaded the high-res version to make sure I have my copy. It's hard subject to get through in just a few minutes, and you did it well. One minor comment: when I first heard of the stratospheric cooling, I also understood it via the mental picture of that "blanketing" effect at the troposphere. But I was surprised to find out it's far more complicated than that. The blanket analogy works for the imbalance period, but the cooler stratosphere is the equilibrium state predicted in the models. Even Gavin Schmidt had a hard time expaining it at RealClimate - which is saying a lot. Ramanathan used another mental picture that I found a bit more enlightening: since the temperature increases with altitude in the stratosphere, more CO2 there would mean less heat coming down (thanks to ScienceOfDoom here).
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11. cdion at 04:50 AM on 8 May, 2010
    Nice slides! I have a question. In the notes, you say: "The greenhouse effect operates day and night so this means nights should be warming faster than days." The logic for this escapes me. Why faster warming during the night?
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12. MarkR at 07:40 AM on 8 May, 2010
    cdion: the argument seems quite complex in the papers I've read (Hansen did one in '95 iirc), involving interactions with clouds too... But one simple explanation might be that days are cooler than nights. Heat flow is related to temperature by something like Planck's Law (accounting for emissivity), dQ/dt = A ε σ T⁴ (that's heat flow proportional to temperature to the power 4, the other symbols are constants). If you change heat flow by a given amount, a hotter thing will warm up less than a cooler thing will. To increase from a T of '1' to a T of '2' requires an increase in heat flow of 15/(Aσε) (from '1' to '16'). To increase from a temp of '5' to a temp of '6' requires an increase in heat flow of 671/(Aσε) units. So if you add a heat flow of 15/(Aσε) from, say, greenhouse gases, you could warm something from 1K to 2K, or from 5K to something like 5.02K. i.e. nights should warm faster than days. Once again though, the real argument seems pretty complex; with the full observations requiring greenhouse gases and cloud changes and scientists seem to take a full paper to explain it! Maybe a quick look at Hansen's '95 paper is worth a go, you've reminded me to check it again when I next have time!
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13. Nichol at 10:58 AM on 8 May, 2010
    very nice slides! Nice the way you start by showing the earth is not in a static equilibrium, but in a dynamic one, with lots of CO2 being released and absorbed, but the natural flows balance each other. The balance is now tipped a bit by burning all those fossil fuels. Likewise with energy: lots of energy arrives from the sun, heating up the earth, and the warm earth radiates off lots of energy, balancing what came in. If we add even a thin blanket of CO2, that balance is shifted, causing the earth to warm up. This non-static equilibrium is not so easy to communicate, and I think you did it very well. ok, as you asked for some nitpicking, I'll try ;) I'm curious to see the effect of water in the graph on page 10, is that to the left, at lower frequencies? (Not sure if you'd want to explain at this point that water can be considered a feed-back, but it would still be nice to have it in the plot). Is 'brightness temperature' proportional to energy flow at a given frequency? I'm a bit confused at how you define a 'temperature' at each given frequency, while the energy per foton is also proportional to frequency (wave number). Looking at this plot naively, one might get the impression that the 'dent' due to CO2 is not as bad as the one from methane. Might be worthwhile if you could remake this plot with axes more easily understandable in terms of energy flow. What is the problem with the nice graph on page 11? Are there no measurements in the US and Canada? The white band across Sudan, Congo, Angola might be easier to understand.. but isn't it still surprisingly blank? About page 14: the warming of the troposphere is not all that obvious, compared to the fluctuations. Also: should the big fluctuations in the top and bottom graphs not be more anti-correlated? OK, after zooming in, I see volcanic eruptions played a role.. tricky plot. Did people get stumble over the subtleties during your talk? page 27: after so many plots about melting ice, you only mention that seawater expands when it warms up. Did people pick up that this effect is not less important than the ice?
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14. barry at 13:09 PM on 8 May, 2010
    The slide show is a great progression of the evidence. Just a couple of nits to pick on the language. From page 2 of the PDF:

    The first step is to work out how human activity is affecting the atmosphere. This graph shows how much carbon dioxide we’ve been emitting over the last 6000 years.

    Might want to rephrase that. How about - "This graph shows atmospheric CO2 concentrations over the last 6000 years. The upswing on the right is CO2 we've emitted since the industrial revolution." Or something better. Near the end:

    Another impact that will have a significant impact on humanity is sea level rise.

    Too many impacts :-) Maybe something like - "Sea level rise will also have a profound impact on humanity." I've bookmarked the slide show for future reference. Nice job.
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15. BC at 20:46 PM on 8 May, 2010
    It was a very good talk so be encouraged to do some more. The people from the St Johns Wood sustainability group near me were also impressed. I had two queries about the slides and they were covered by Nichol at 13 above - slide 10 not showing any H2O yet its one of the strongest greenhouse gasses and slide 11 being blank for the US and Canada. This one I noticed during the talk.
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    Response: Slide 11, the map of downward infrared radiation, comes from Wang 2009. It shows the trend in downward infrared radiation over 1973 to 2008 and only includes stations that have at least 25 years worth of data. There's no U.S. or Canadian data because they switched their cloud observation method from human visual measurement to instrumental in the 1990s.
    
16. BC at 20:59 PM on 8 May, 2010
    One point that I have trouble with and that came to mind again during the talk is that with higher temperature we have more water in the atmosphere. This brings to mind a hotter, wetter jungle type and fertile enviromnment yet your talk mentioned more droughts and dryer conditions. The handout at the talk mentioned that Australia has had 1C temperture rise in the last four? decades. I hadn't realised that we were warming faster that the world average.
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17. The Skeptical Chymist at 00:35 AM on 9 May, 2010
    BC, I checked the handout, which says there has been around 1C of temperature rise across OZ since 1950, I double checked this on the BOM website. This does suggest Australia is warming faster than the world average, although I imagine part of this is because the world average includes ocean temperatures which are warming more slowly than land temperatures. If you are interested in climate changes in Australia then I recommend the BOM & CSIRO "State of the climate" report that was released recently. It's only 6 pages, but it's highly informative.
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18. Mike_Allen at 18:26 PM on 9 May, 2010
    Thanks for tha,t the presentation left me more than a tad concerned. What about a badge for websites concerned about climate change? Is anyone doing this. I don't like being called "warmist" or "CAGW", but I am concerned and would like to raise this as a concern but not like a pink ribbon sort of thing. Maybe a Facebook page would be good for concerned Aussie people.
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19. CBDunkerson at 21:04 PM on 10 May, 2010
    cdion #11, once the Sun goes down the Earth begins losing heat fast. The greenhouse effect slows down the rate of heat loss. Thus, a more pronounced greenhouse effect means that nights stay closer to daytime temperatures longer. This 'heat loss' anomaly is greater than the increased daytime temperature anomaly from the enhanced greenhouse effect and the source of the bit about nights warming faster than days. Basically, if GHGs make the average daytime temp 1 C hotter they might make the average night temp 2 C hotter... because the temperature doesn't drop as fast as it used to. barry #14, no the slide really is meant to be human (industrial) emissions. There is a separate slide right after that for atmospheric levels. The intent is to show that atmospheric levels have grown as our emissions have. The emissions charts I've seen are generally calculated estimates based on fuel sources used, population, and industry. Nichol #13, as you surmised the H20 impact is off the left side of that chart... as is most of the CO2 impact. My recollection is that the study didn't show that section because they were unable to differentiate between the two.
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    Response: "My recollection is that the study didn't show that section because they were unable to differentiate between the two."
    
    Actually, the chart doesn't go further into the CO2 band because the uncertainty of the data gets too large - they had to cut it off when the uncertainty range got large. That particular graph shows the change in outgoing energy with the humidity effects removed. The point of that graph is to isolate the effect of trace gases.
    
20. BC at 21:19 PM on 10 May, 2010
    Mike, Thanks for the two links. I see where they got the 1C rise since 1950 in the BOM site. The 'State of the Climate' read is a bit worrying for Australia. No different to most of the rest of the world though.
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