This is part of my critical review of the palaeoenvironmental evidence for the influence of solar activity on climate.
Chen et al (2013) Paleoclimate of the Southern Adriatic Sea region during the ‘Medieval Climate Anomaly’ reflected by organic walled dinoflagellate cysts. The Holocene 23: 645-655.
I found Chen et al (2013) via Maarten Blaauw’s Club du Soleil, which lists papers relevant to solar forcing of climate. Having concluded that the previous paper by Chen et al (2011) was not credible evidence of a solar-climate relationship, I thought I would look at their new paper.
Chen et al (2011) covers the period 60 BC–AD 200 from a core off the south coast of Italy. Chen et al (2013) covers the Medieval Climate Anomaly, AD 990–AD 1200. An interesting publication strategy: take one core and publish two-three hundred-year segments of the proxy data, rinse and repeat the site description and methods and add the new results. I look forward to the other ten papers they will be able to write from their 3600 year long core. I particularly look forward to the one covering the last 300 years, so the comparison with the instrumental record can validate, or otherwise, their dinocyst indices.
Like Chen et al (2011), the more recent paper calculates indices based on the dinocyst assemblages in their core and subjects these data to spectral analysis and plots the proxies with other proxy data for comparison. The spectral analysis is simplified in Chen et al (2013), using only REDFIT, and finds cycles at 11.4 and 26 years in one proxy and at about 9 and 13 years in the other two. The 11.4 year cycle in the dinocyst temperature index is described as “strong support” for a solar activity-climate relationship. I demur. In the absence of a strong, clear, and widespread 11-year cycle in the instrumental record that can be related to solar activity climate, it is folly to believe that an 11-year cycle in noisy palaeoenvironmental data is solar driven. The alternative hypotheses, that it is chance or some internal cycle, are much more plausible.
The other line of evidence in Chen et al (2013) in an alleged correlation between the Δ14C anomalies and the dinocyst temperature index. The close link is determined by eyeballing the graph. The correlation coefficient is not calculated; autocorrelation is not accounted for; no significance is estimated.
The correlation in the raw data looks weak. The correlation in the smoothed data looks stronger, but of course has fewer degrees of freedom. I doubt that the relationship is statistically significant, and that is before chronological uncertainties are considered.
Chen et al (2013) are aware of the possible impact of chronological uncertainties: “… the sediments of the core section could have been sedimented about 180 years earlier or later compared with our assumption.”. So 180 years of potential error in a section of core that is 210 years long. This calls into doubt even the sign of the correlation Chen et al (2013) eyeball.
The sediment core is the same in Chen et al (2013) and Chen et al (2011), the methods are the same, and my conclusions are the same: this paper contains no credible evidence of a solar-climate relationship.