Anything related to climate change is labeled "political" by the large well funded anti-science, pro climate science denial lobbies.
Having not seen it, I can't really be certain, but it would appear from other comments that have not been disputed that part of the movie mocks politicians. That would generally be considered political. It is said to include footage of "Stephen Colbert making fun of the NC legislators", which would seem, as it is a clip from a political comedy show, a fairly clear cut case of it being political.
Just because there are global warming documentaries that are falsely accused of being political does not mean that no movie about the subject can ever be made that is not political.
Of course, not having seen it, it could also be legitimate commentary on the news coverage. Or even a anti-global warming movie mocking Steven Colbert's style as typifying coverage. I have no idea -- and am comfortable saying that I don't know. But it is silly to say that no movie on the subject can be political in nature just because some are falsely accused, and from the clips that have been discussed, it does seem to, at least in part, lean toward that more political side of things.