The thing about climate change in prehistory is that it drives changes to human life. Archaeologists put glacial maxima on their timelines because it's such an important factor when trying to understanding human migration, the spread of new technologies that do better in drier or wetter climates, the shift to different food sources, and so on. This predates the current climate-aware political landscape.
If 90% of a species is killed off by climate change, and if for hundreds of thousands of years that species survived glacial maxima in reservoir populations in areas that are now populated by starving humans who kill the remaining 10%, was it the climate or the humans who wiped out the species? The changing climate killed more, but the humans were the differentiating factor, so which one do you point the finger at?
I don't think it's right to call that denialism.