Look at this logically. Think about this: Did man's activities back then cause climate change? No because man's activities were not like they have been since the industrial revolution. So your supposition of man made ice ages is wrong. But look at climate change today and at some of the conditions that may have caused the ice ages back then and other non man made conditions you may think of that are causing climate change today-- a lot of science went into trying to prove with data that many non-man-made conditions are causing climate change (and this approach looking for non-man-made causes continues today), but the best explanation from science is that man-made-activity is the explanation that best explains the data.   https://www.bloomberg.com/graphics/2015-whats-warming-the-world/