Impact of the ~ 2400 yr solar cycle on climate and human societies

Judith Curry
For this article I am going to concentrate mainly on the ~ 2400-yr cycle during the Holocene and on its effects both on climate and people. It is important to highlight two things. First, that solar variability, even if an important factor affecting climate change is neither the main one, nor the only one. Temperatures on Earth appear to depend mainly on orbital changes, firstly obliquity, but also precession and eccentricity, and oceanic cycles, and volcanic activity also play an important role at times, and therefore solar variability alone does not explain climate changes. The second is that solar cycles are irregular in nature. The Schwabe cycle is a good example. Although described as an 11-yr cycle it can be anywhere from 8 to 15 years. Also its amplitude is very variable, and during the Maunder minimum between 1620 and 1700 AD even became inconspicuous. Other solar cycles also manifest this irregularity both in periodicity and amplitude, and similarly the ~ 1000-yr Eddy cycle was inconspicuous between 4500 and 1500 yr BP (years before 1950)."