There is no history of this happening before, at least not on the time frames we are talking about here. This is thousands of years of change in decades. It isn't so much just the change but the pace that is the issue. Like how jumping off a building and taking the elevator achieve the same amount of change but on a very different time frame and thus very different results.
That is a good question but I suspect we wouldn't know. Just educated guesses and I cannot find those at the moment.
I think the other big issue is that back then we didn't have industrial civilization and high level agriculture dependent on specific environmental factors.
