[C210N]

Yes, sunspots *have* been observed in detail that long. Although methods have improved, there is some degree of allowances for ensuring numbers today match numbers from way back in the apples-to-apples sense - there are different number systems, to make this work.

And, yes, there are other effects. Like thermometer readings from way back and frozen Thames river events.

[rktman]

Back in the 1920’s early 30’s my dad and grandad used cut ice out of the Hudson River around the Athens NY area for ‘refrigeration’ needs. Does it even freeze solid these days? Must be glow bull climate discombobulation.

[Tanniker Smith]

Thanks. I know there secondary effects because I know that they get attributed to sunspots. I was just curious if they were using that knowledge to work backward through time and calculate/estimate sunspot activity of if they could do it back then.

Interesting. Good to know.