Francois O writes in:
For those interested in the role of the Sun on the climate, and how reconstructions can be used to assess it, there is an interesting paper just out in JGR by Nicola Scafetta and B J West. The paper is available here. This is a continuation of their previous work. Basically they use a phenomenological approach. So instead of taking the reconstructed TSI values, plug them into a model, and find that indeed the Sun has only a minor influence (like Ammann et al. did in their PNAS paper of March 6, 2007 | vol. 104 | no. 10 | 3713-3718 ), they make no prior assumption on the total Solar forcing. They just assume, mostly rightly, that the Sun was the main driver of climate variability. Then from the solar reconstruction and the temperature reconstruction, they deduce which model of solar forcing best matches the two together.
They have a nice discussion in the introduction about the pitfalls of the usual method. For the record, even though they use both Mann03 and Moberg05 reconstructions, they refer to MM05 and the Wegman report as pointing to the flaws of Mann03.
This is all to show that temperature reconstructions do play an important role in understanding the human role on climate.
I’ve not spent as much time on Nicola Scafetta’s work as I would like to have. I spent about an hour with him at last year’s AGU and he gave an impressive explanation of his ideas. One of the fundamental assumptions of modern models (as I understand it) is that all “forcings” are equal. “Forcings” is a useful metaphor but what if, for some reason, all forcings are not the same. For example, it doesn’t seem inconceivable to me that 1 wm-2 of solar forcing (visible wave length, high energy photons, low entropy) could have a different effect than 1 wm-2 of GHG “forcing” (infrared, low energy, high entropy). I’m not saying that they do or don’t; I haven’t studied the issue in any detail – just that I don’t see the harm in working through the assumptions of non-equal forcing “efficacy”. Mathematicians like to work through the analysis of alternative axioms to see what happens and it’s hard to see that any harm would result in this case. Arguably Scafetta finds empirical evidence suggesting that this may actually be the case.
I don’t vouch for this paper as I have merely skimmed it and have not even begun to work through the details. At this point, I am threading it for discussion.