What are the lines of evidence for human impact on global climate change?
During the reign of Genghis Khan atmospheric carbon decreased.
The only time in human history that we see a decrease in atmospheric carbon is during the reign of Genghis Khan, coinciding with the fact that he killed around 15% of the population of the Earth. The unique thing about the Mongol empire over other events that resulted in mass death, was that they killed everyone in entire areas, unlike a plague which might kill a lot of people but does not wipe out the whole town. As such forests where allowed to regrow in large areas. This evidence suggests the reason that atmospheric carbon went down was due to the lack of human activity in areas that used to have it. The conclusion that has been drawn is that human activity directly affects carbon in the atmosphere which we know affects climate change.