Or are some of them simply artifacts and not solar variability cycles?Instead of assuming every peak in a frequency analysis constitutes sufficient evidence for the existence of a cycle, I only consider those where abundant evidence exists in the scientific literature that solar cycles match the climate evidence precisely. Of interest are also the periodicities recognizable in the sunspot record, the Schwabe (11-year), Pentadecadal, and Centennial (Feynman) cycles. Of the 25 GSM identified by Usoskin (2017) during the Holocene, only three are not located close to the lows of the Eddy or Bray cycles.
The result is reproduced using a Be solar activity reconstruction. As the evidence indicates this periodicity is not currently relevant, we will not consider it further.
Additional periodic climate variability in the centennial to millennial range is produced by the 1500-year oceanic cycle, and by several solar activity periodicities that, according to numerous authors, correlate well with climate variability. E8 (8,300 BP) coincided with the outbreak of Lake Agassiz, and researchers are trying to differentiate the relative climatic contribution to the 8.2 kyr event from the solar minimum and the proglacial lake outbreak (Rohling & Pälike, 2005). Usoskin (2017) gives a conservative list of 25 GSM that were identified in previous studies by different researchers for the past 11,500 years. Since the Eddy cycle is so close to one thousand years, all the lows of the cycle take place at ~ X,300 yr BP, with X being every millennia of the Holocene. a) Left scale: Reconstructed Northern Hemisphere mean MJJA temperature anomaly time series (black line), smoothed with a 30-year Gaussian filter. A continuous in phase coherence between tree-ring temperatures and solar activity is seen at the de Vries periodicity. The synchronization, and in some cases amplitude, of the climatic signal correlates with the strength of the solar signal, indicating that the modulation of the de Vries cycle by the Bray cycle extends to its climatic effect. The 88-year Gleissberg solar cycle Despite the popularity of the Gleissberg solar cycle in the literature I have not been able to unambiguously identify this cycle as important for solar-climate effects.
The study of solar cycles and their climatic effect is hampered by a very short observational record (~ 400 years), an inadequate understanding of the physical causes that might produce centennial to millennial changes in solar activity, and an inadequate knowledge of how such changes produce their climatic effect. E7 (7,300 BP) coincides with the last cold, humid phase of the sixth millennium BC (Berger et al., 2016). We can observe in the list of GSM that 15 of them take place at ~ X,300 ± 80 yr BP (figure 83 a; Usoskin, 2017). Right scale: Solar forcing relative to the period 1976-2006 CE, with the pink shaded region showing the range of the forcing reconstructions compiled by Schmidt et al. This is due to the Gleissberg cycle being different things for different researchers.
Wavelet analysis shows the ~ 1000-year periodicity having a strong signal between 11,500 and 4,000 yr BP, and between 2,000 and 0 yr BP, but a very low signal between 4,000 and 2,000 yr BP (figure 79; Ma 2007; Kern et al., 2012). Several authors have noticed this solar forcing dominance during the early Holocene (figure 41; Debret et al., 2007; Simonneau et al., 2014). b) Holocene record of North Atlantic iceberg activity determined by the presence of drift-ice petrological tracers. When the amplitude of the 1000-year solar signal is adjusted by its wavelet power (figure 81), a high correlation between North Atlantic iceberg activity and the 980-year Eddy solar cycle corresponds to the periods when the 1000-year solar signal is high, while the correlation is low at periods of weak 1000-year solar signal, strengthening the relationship between climatic Bond events and solar activity, that has been acknowledged by multiple authors, starting with Gerald Bond himself (Bond et al., 2001). Black curve, a 1000-year frequency cycle representing solar activity for that periodicity, whose amplitude reflects the relative power (colored bar) of that frequency in a solar activity reconstruction wavelet analysis. Two of these GSM, at 10,165 and 5,275 years BP, also coincide with the Eddy cycle, as both cycles tend to coincide in phase when two Bray cycles (4,950 years), and five Eddy cycles (4,900 years) have passed. The name refers in some cases to a GSM cluster (cl.). As originally described, the Gleissberg cycle is unacceptable by modern scientific standards (and I would dare to say inexistent), and due to it the term Gleissberg cycle means different things to different authors.
The average duration of the ~ 1000-year cycle can be calculated from the grand solar minimum at 11,115 yr BP to the one at 1,265 yr BP (dates from Usoskin et al., 2016) for ten periods at 985 years, a span in very good agreement with the calculated 970 years from frequency analysis (Kern et al., 2012) and the calculated 983.4 years from astronomical cycles (Scafetta, 2012). The 980-year Eddy cycle in solar activity reconstructions. The Bond series of North Atlantic drift-ice record reflects a clear ~ 1000-year periodicity during the first 6,500 years of the Holocene that correlates with the 980-year Eddy solar cycle (figures 48 & 80; Debret et al., 2007). The 980-year Eddy cycle correspondence to Bond events. The unusually long Roman Warm Period (2500-1600 BP; Wang et al., 2012) coincided with the final part of this interval of low Eddy solar cycle activity, while known warm and cold periods have faithfully followed the since strengthened 980-year Eddy solar cycle (figure 81). North Atlantic iceberg activity and the Eddy solar cycle. The cycle states if the GSM shows a temporal coincidence with a low from the Bray (B), or Eddy (E) cycle. For some authors it is a frequency peak of ~ 88 years that appears in frequency analysis of the cosmogenic record (Mc Cracken et al., 2013b; Knudsen et al., 2011; figure 86).