"Studies of stratigraphic data suggested that the solar cycles have been active for hundreds of millions of years, if not longer; measuring varves in precambrian sedimentary rock has revealed repeating peaks in layer thickness, at roughly eleven-year intervals. It is possible that the early atmosphere on earth was more sensitive to changes in solar radiation than today, so that greater glacial melting (and thicker sediment deposits) occurred during years with greater sunspot activity."
"Though the connection between sunspot activity and the earth's climate is still being debated, it is known that a period of unusually low sunspot activity from 1645-1715, called the Maunder Minimum, coincided with a period of long cold winters and severe cold temperatures in Western Europe, often called the "Little Ice Age."
Does CO2 cause sunspots?
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