Nobody’s Perfect

Thanks to Dave for pointing this out.  Blogland has been active the last couple of days.  Below is an unusually humble reply by Gavin Schmidt at Lucia’s blackboard written In response to Dr. Scafettas post on Dr. Peilke’s blog which criticized an obvious mistake in their paper.  It’s funny because he implies that Dr. Scafetta won’t release the code, I wonder if he asked.  Either way RC’s proprietor showed a bit of class.

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Gavin realclimate.org (Comment#17440) August 6th, 2009 at 2:34 pm Nice to see that so many people are interested in our paper!

I’ll make a few points here since the discussion seems a little more focused than in other venues….

First off, B&S09 clearly stated that we had not been able to fully emulate Scafetta and West’s methodology and so statements that we did something different to them were to be expected. The issue with the periodic vs. reflection boundary conditions in the wavelet decomposition does make a difference – but what they used was never stated in any of their papers (look it up!). The amplitude issue is also valid, but actually has no implication for the calculation since it is the ratio of two amplitudes that goes into the empirical model that S&W use. The factor of 2 cancels out.

Secondly, this will all end up being beside the point. The real issue that we were trying to address is that many methods used to calculate attributions – like S&W or multi-linear regressions – are very sensitive to co-linear forcings (i.e. increases in both CO2 and solar) and unforced noise (particular in frequency bands that are being specially selected for). In the test cases we looked at (different GCM simulations using different sets of forcings) we knew what the answer should have been, and these methods were not able to correctly identify the actual solar trends.

This is true for our emulation of S&W (even including a switch to a different boundary treatment for the wavelets) and very likely to their version as well. (Note we still don’t have a perfect emulation, so perhaps you guys could agitate for some ‘code freeing’ to help out ). (NB. I don’t think that wavelet analysis really helps very much for this problem – more standard band-pass filtering gives similar results. We only used it because S&W did).

Third, a couple of people commented on the issue of the which solar reconstructions should be used. I am actually working with a number of groups to update these estimates for the AR5 models, but the reason why we used Lean (2000) in the paper was simply because that was what the model simulations had been run with back in 2004 (and which were what we had available). I have no reason to prefer that over any more up-to-date reconstruction and GISS (at least) will be using one of them in the AR5 runs. To a large extent the point is moot in this paper since the idea was to detect something we knew was there – because if a method doesn’t work when you know the right answer, it is unlikely to work in the real world where you don’t.

Finally, in case anyone was in any doubt, I plead guilty to not being perfect.

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I offered to request any code he required for replication over at the blackboard if he can narrow down what he’s looking for.  My opinion is that we should keep it clean and be nice to Dr. Schmidt, there’s no point in kicking someone when they’re down.  He probably will answer a few questions if things remain polite over at Lucia’s so check it out.