Thats is an odd graph. everyone that i have seen shown a up slope in those years. why is this one different?
Could possbly be because it is a temperature history for Albany, New York, as opposed to the few places on the earth where temperture trends happen to be positive enough to make a global index look positive.
click yer clicker thang here >>> Data @ NASA GISS Surface Temperature Analysis Maps
All depends on the temperature datasets used and how you weight/adjust them constructing an index. [ssspt, just ignore that little man behind the curtain]
I copied all your graphs. Yours are the best! I hope you don’t mind? The ‘most common’ one up there is from you.