More fun with Schwartz

Thanks to Inel for finding this; look there for the links. So Schwartz (yes that Schwartz) said: “The latest report from the Intergovernmental Panel on Climate Change assesses the skill of climate models by their ability to reproduce warming over the twentieth century, but in doing so may give a false sense of their predictive capability”. Exactly why they think this gets quite messy but seems to amount to not knowing the aerosol forcing too well; and they go on to link this to AR4 estimates for climate sensitivity.

This reads wrong to me; and Forster et al reply “However, they have misinterpreted the use of AR4 Fig. SPM-4 (shown here as Fig. 1) and, as such, their criticisms are misplaced” which seems right: “the AR4 assessment did not derive estimates of climate sensitivity, of future warming, or of past warming attributable to greenhouse gases directly from these simulations”, which I don’t think S et al have fully grokked.

S et all reply that F et al “mainly criticize us for points which we did not make regarding climate sensitivity and future global warming and fail to come to grips with our central point, namely that in assessing the skill of climate models by their ability to reproduce warming over the twentieth century, the latest report from the IPCC3 may give a false sense of their predictive capability”, but I think they have misunderstood again (or are perhaps redefining what their main point was). I took their main point to be the climate sensitivity estimates; they don’t seem to appreciate F et al’s point about where these come from.

[Update: JA doesn't think much of it either]


  1. #1 sinned34

    Damn, I hate it when I get my Schwartz all twisted.

  2. Eli,

    I have some speculations on this on my blog, but I’m just guessing. Where is the response to S et al?

  3. Sorry about misspelling your name! William. I knew it had an “i” in it.

  4. OK, so now I’ve read inel’s comment and am really confused. SS is not talking about the green bar, right, so what is that all about? I am now almost as confused as I was after reading Lubos’s explanation – Gavin’s hands, Castro’s GDP and all.

    [Dunno wot the green bar is there for at all. Uncertainty from scenario uncertainty is a totally different matter. JA, commenting on the earlier SS, thought that SS was out of his depth. It possible that he is simply confused - as far as I (and more exalted folk such as Forster and JA) can tell, he has simply misunderstood how things are done.

    As for Lubos, well, he is there for light relief I assume -W]

  5. #5 inel

    Sorry I confused you, CIP. I was rabbiting on (to William, really) about the green bar because that was obviously added for marketing purposes. The way non-scientists/busy execs/professional skeptics use papers like this is they hear “it appeared in Nature”, read the headline, look at the supporting chart, see that it looks technical, and rarely make it past the first page. But they remember it exists.

    So, since the document is selling the idea that climate models are lousy predictors of future warming, the title, intro and graphic support that goal, and the final sentence says what should be done about it, i.e. more research.

    Anyone vaguely familiar with the latest IPCC report will probably recognise the figure showing radiative forcing components, but may not realise that the green bar was added. It stands out, visually.

    That green bar was added to reinforce the theme that not only are there ‘error bars’ for radiative forcing in 2005, but when you look ahead to 2100, the total projected forcing has an enormous degree of uncertainty associated with it. The fact that that particular uncertainty is actually the “range of estimates for different emissions scenarios” in a little over 92 years’ time, is not clear to most readers who skim rather than use a toothcomb. That the two definitions of uncertainty for the 2005 and the projected 2100 bars are completely different would not even be noticed. Instead, the thought is sown: “How could anyone rely on this wide-ranging guesstimate for planning purposes? Ridiculous!” This reaction, of course, agrees nicely with the proposition that quantifying uncertainty is painting too rosy a picture, because predictive capabilities have hereby been shown to provide insufficient confidence for decision-making.

    So, I agree with William that SS could be confused. However, I also think S et al are clutching at straws in an attempt to make a case that will not stand scientific scrutiny … but not to worry, because scientists, after all, are not the intended audience for such a marketing document. The target audience consists of those who want a paper to quote to “prove” that the IPCC and climate models are too flaky to trust, therefore no action should be taken to combat climate change, apart from honouring this call from scientists for more research to reduce the “uncertainty in Earth’s climate sensitivity”.

    P.S. That’s my own interpretation. I have not read anyone else’s comments on this, so apologise if I am repeating what you may have read elsewhere. Basically S et al are talking cross-purposes with F et al, hence the odd sense of the “Authors’ response” that concluded this exchange of correspondence.