There is evidence in the paleoclimatic record that significant climatic climate changes have occurred at the same times as solar magnetic field changes. (The solar magnetic field changes affect the amount of isotopes produced in the earth’s atmosphere. The high amount of these isotopes provides a tracer to identify the solar changes.)
The paper “The role of solar forcing upon climate change” by Van Geel, linked below provides a summary.
The last significant solar/climatic event occurred 1400 years ago. There is some evidence of a 1470 year and 2400 year strong cycle in solar magnetic field. There is also some evidence of a 180 year cycle. Some of the weak cycle solar predictions for cycle 24/25 are based on the isotopic data.
I became interested in solar physics and solar mechanisms which could modulate climate after reading Mayewski’s Ice Chronicles which summaries the evidence for abrupt climate change from an analysis of the Greenland Ice core data.
I am not aware of any single mainstream theory as to why the solar magnetic field would be cyclically varying. There are, however, some interesting speculative papers and recent solar data.
http://www.gg.rhbnc.ac.uk/elias/teaching/VanGeel.pdf
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…Bond et al. (1997) found evidence for ice-rafting events during the Holocene at 1400, 2800, 4200, 5900, 8100, 9400, 10,300 and 11,100 cal. BP (my comment, BP, Before present.) and during the Last Glacial at a similar timing as the Dansgaard-Oeschger events. They identified that these climatic shifts occurred with a cyclicity of 1470 years, and conclude that solar B. van Geel et al. / Quaternary Science Reviews 18 (1999) forcing of these cyclic events…
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...Mayewski et al. (1997) showed that a 1450 periodicity is present in the band pass component of both the 14C residual series derived from tree rings and glaciochemical series from the GISP2 ice core, believed to reflect changes in the polar atmospheric circulation…
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…The latter periodicity is in agreement with the cycle of about 2600 year in North Atlantic climate shifts as deduced from analyses in Greenland ice cores (Dansgaard et al., 1984; OÕBrien et al., 1995). Furthermore, this cycle is close to the 2400-year cycle, believed to be of heliomagnetic origin, known from the 14C record in tree rings (Stuiver and Braziunas, 1989)…
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Comment:
When the paleoclimatic data was discovered that showed evidence of cyclic abrupt climate changes, cyclic changes in ocean currents were hypothesized to cause the changes. Recent paleo data, however, shows the climatic changes occurred simultaneously in both hemispheres which supports a planetary modulating mechanism such as solar modulation of clouds, rather than ocean current changes which primarily affect a single region.