Answers in order: We dont' know. 5 times. The rapid and huge increase in CO2 is to my knowledge unprecedented. We did have similar CO2 levels in the past but

Answers in order: We dont' know. 5 times. The rapid and huge increase in CO2 is to my knowledge unprecedented. We did have similar CO2 levels in the past but never in such a rapid incline, only after thousands if not millions of years time for everything else to respond. We could be causing a The-Day-After-Tomorrow-Scenario. Or something like 2012. Or Mad Max. We simply don't know but considering the parts we do know, it's likely that whatever happens is not good. A 400ppm Level of CO2 was considered a symbolic point of no return and we have passed it a while ago.