we only have large-scale climate readings for the last 100 years or so. Past that it's sparse readings, interpolations and projections.
...And these paintings: .
http://en.wikipedia.org/wiki/Maunder_Minimum
http://en.wikipedia.org/wiki/Little_Ice_Age
http://en.wikipedia.org/wiki/Little_Ice_Age#Depictions_of_wi... http://en.wikipedia.org/wiki/Hendrick_Avercamp