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W/S/M correspond to the Wolff, Spörer, and Maunder minima. a) Lomb-Scargle spectrogram on C solar activity reconstruction data grouped in 2000-yr windows, showing the distribution of spectral power for the 50-125 year range. This explains why the cycle cannot be detected in the sunspot record.

The 208-year de Vries solar cycle As previously described (see The 2400-year Bray Cycle), the de Vries solar cycle is strongly modulated by the Bray solar cycle.

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.

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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.

Since 88% GSM occur during an Eddy or Bray low, it is unlikely that the next GSM will take place before ~ 2600 AD, when the next Eddy cycle low is expected.

The Oort (920 BP), Noach (4805 BP), and an unnamed GSM at 8995 BP, that could be considered part of the Boreal 2 cluster.

Other solar periodicities By now it should be obvious that solar cycles are pseudocycles or periodicities that display a relatively high level of period and amplitude variability.

Some of the cycles, like the ~ 2400-year Bray and the ~ 1000-year Eddy cycle, appear to be featured in records several million years old (Kern et al., 2012).

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