You misread my post. I said longer-term climate change does NOT mean that people can NOT possibly have affected things. The two are separate issues.
The climate of the earth has been changing for billions of years on its own, but that does not mean people cannot have affected it in recent times. Just doesn't logically follow.
You meant it just doesn't follow that they CANNOT have affected it. Well, that's logical of course. It's important to remember that it is POSSIBLE that man has affected the climate. OK.
I was saying something more relevant, which is that it is "logical" in a certain way that we HAVE affected it.