I think with how slow evolution happens, bad is anything that isn't the status quo. Yes, some species that are more adaptable will survive and could even thrive as competitors die off, but many more species will go extinct. It's hard to imagine any path here (at least on a short to medium term timescale) where biodiversity increases. And given that biodiversity is what got us to where we are, I think it's easy to agree that it's a good thing, so anything that threatens it is bad.
> All that said, I don’t think we have the computational models to predict what happens when you increase the temperature on earth for a century.
This definitely seems true. As a layman it seems like this is a classic case where chaos theory comes into play. Even tiny errors in our projections will lead to wildly different outcomes, so the only thing that we can say for sure is that we don't know. That's scary.