It was suggested by Sir William Herschel about 200 years ago that changes in the growing season for wheat in England could be related to the 11-year sunspot cycle. He speculated that there was a change in the luminosity of the Sun that was correlated with the sunspot variation, and that it affected precipitation and the winds. As discussed recently in Eos by Lean and Rind , the luminosity of the Sun does vary on the 11-year cycle, but only by about one part in 103, which is too small to explain such a change in the weather.
Lean and Rind argue that on the 200-year (Maunder) timescale a larger change, by up to 2.5 parts in 103, is plausible. This would then provide for about a 0.46°C change in global mean temperature, and could account for as much as half of the cooling usually associated with the coldest part of the little ice age.