Are Tibetan chironomids mesmerised by solar variability?

It’s been a while since I examined a paper that purports to present palaeoecological evidence for a climate response to solar variability. But last night, flicking through the recently published papers in Quaternary Science Reviews, I came across Zhang et al who suggest in their abstract that “solar activity could be an important mechanism driving the centennial-scale variability“.

Zhang et al present a high-resolution (50-yr) Holocene chironomid stratigraphy from the small Lake Tiancai on the south-east margin of the Qinghai-Tibetan Plateau from which they use a transfer function to infer Holocene temperature evolution. Unlike many authors, they present a range of transfer function diagnostics. These suggest there may be some problems with poor analogues for the fossil samples, especially in the late glacial/early Holocene, in the modern calibration set.

So far, so good. But what of the solar variability?

Alas, it is a correlation-by-eye.

Zhang et al Fig. 5. Multi-proxy records compared from Tiancai Lake (a) the percentage abundance of a pollen genus Tsuga; (b) December insolation at 30 °N; (c) chironomid-based mean July temperature reconstruction from this study (solid black line) with 5-point-running average (red solid line) highlighting the overall trend and (d) the percentage abundance of a diatom species Aulacoseira alpigena. Highlighted areas in blue correspond to the recognized Hallstatt solar cycle minima centered at 8200, 5500, 2500 and 500 cal yr BP.

Although the total solar irradiance reconstruction from Steinhilber et al. is shown in figure 6, figure 5 shows the totality of evidence for a link between chironomid-inferred temperatures and solar activity at Tiancai Lake. No statistical tests are used to test if this relationship is better than expected by chance.

The 5-point running-average has obviously been miscalculated – it should never reach the extremes of the data – it appears to be joining every fifth sample instead (it is done correctly in figure 6). This makes comparison of the smoothed record with the solar minima more difficult. Only one of the solar minima convincingly aligns with a temperature minimum and other large temperature minima do not align.

I would argue that this paper provides absolutely no evidence for a solar-temperature link, and that the purported link is a distraction to an otherwise good paper.

So, fulfilling Betteridge’s law of headlines, no, the chironomids were not mesmerised by solar variability. But the authors, reviewers and editors might well have been.