And it took way longer than a few decades to get there hmm...? Systems had time to adapt, including new animals evolving. For example trees species habitable zones migrate north or south in response to a changing climate, but to do that the northern most edge of the habitable zone for that species at the time a tree starts is life needs to stay within the southernmost edge until that trees dies, otherwise they can't move fast enough. So the whole zone can't move further than the width of it within, what 500 years? At a wild guess. Depending in the average lifetime of the tree species. Other systems involve evolution to adapt which takes a lot longer. That's an over simplification of course, and I'm not a scientist, but those are not timescales we've got.