Graph goes back to 10000BC, which is when farming started. Source is on the graph...some UK organization...had a lot of data. I thought this was pretty self evident, and not a controversial graph. If you can succeed in nitpicking their data (I will be impressed with your dedication), you can't deny the trend indicated on that graph.
Saying that the natural (non-man-caused) warming temperatures and the resulting retreat of glaciers didn't open up a lot of farm land is like arguing that the sky is not blue.
This message has been edited 5 time(s).