A phenomenological sequel


Does climate sensitivity depend on the cause of the change?

Can a response to a forcing wait and then bounce up after a period of inertness?

Does the existence of an 11-year time-scale prove the existence of solar forcing?

Why does the amplitude of the secular response drop when a long-term trend is added?

These are perhaps some of the questions that we might hope to see discussed in the sequel to the sequel on solar forcing by Scafetta & West (S&W), a few of which have been discussed before here and here. (I still think those earlier studies were seriously flawed and showed a lack of scientific understanding, by the way).

This time S&W present a set of new arguments and a new set of results which are scattered all over the place. The impression from reading their paper is that the upper range (they call it ‘upper limit’) is probably more representative than the lower estimates for the solar contribution to the global mean temperature.

I think that many of their arguments, on which this impression is built, are shortsighted. For instance, they claim that certain climate reconstructions must be wrong because they give ‘unphysical’ answers. But there is another explanation too that they did not contemplate: their idealistic (one may also argue unphysical) model may also be wrong! Thus, they fail to exclude other explanations.

S&W attach the ACRIM Total Solar Irradiance (TSI) product (not the PMOD product, probably because that does not show any trend) to a TSI reconstruction (Lean 2000 TSI [see Lean, 2004], or Wang et al., 2005) in such a way that the average reconstructed TSI value over 1980-1991 corresponds with the ACRIM mean for the same period – never mind the discrepancies in trend and that such cavalier stitching of data series is one of the deadly sins in climatology (hint: the series is inhomogeneous).

One new aspect of this S&W study is the focus on ‘feedbacks’. They assume the TSI reconstruction is a proxy for the total solar influence and that CO2 is part of a solar ‘feedback’ (isotope ratios suggest the CO2 comes from deep underground reservoirs, but it’s not clear how the sun manages to dig up this carbon from deep below Earth’s surface).

S&W maintain that the climate response is greater for longer time scales (which is reasonable) as illustrated in their figure 4 (reproduced below), and assisted by the simple model illustrated in this figure, they argue that the present warming is a delayed response to past solar changes (presumably before the 1950s). But it is unclear why the temperature then flattened out and even dropped a little between 1940-1970 at the time when it really should have increased fastest. One could argue that something else also happened then, but for an unknown reason, this forcing then seemed to have a shorter relaxation time. Why such an interference would give a quicker response than a solar signal is unexplained (the response to volcanoes is fairly prompt, however).

S&W figure 4

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