So the scope of the report and the film may have defects. Does that automatically negate the real world situation that the polar ice caps are melting? No.
I do believe that the planet has a natural system for adjusting the CO, if that means wiping out higher forms of life then so be it. The threat of this happening is real however when and how is something science can't put a finger on and to a lesser extent drive policy that completely fixes the problem in one go.
Science is telling us that what has happened in the past is X based on parameters Y & Z however we don't know the exact set of parameters (we are missing some) and the planet changes state over time (ie sea currents change etc based on undersea landslides, tectonic shift etc).
So what we can do is look for the reasonable suggestions - CO2, ozone etc and place policy to fix those points. In the end the human race will cause changes and the planet will need to balance itself back to a stable state. It just so happens that we're changing it too quickly for a smooth balance so expect extreme changes.. don't need to be a brain surgeon to work that one out based on a globally closed system..