We've been tracking sunspots for a long time. This history of cycles graphic shows the cycles and their strength going back to the 15th century. See that dip in cycle strength in the early 1800's? That's known as the 'Dalton' minimum and resulted in cooler temperatures in Europe.
I love this painting. It shows the Thames river in London frozen solid during that Dalton minimum. When's the last time you heard of the Thames freezing over? Not in your lifetime. It is theorized that this reduction in sunspot activity during the Dalton and Maunder minimums caused global temperature drops, and much harsher and longer winters.
