I have a lot of thoughts on this subject and the subject of global warming which would probably get me run off this board, but would make an interesting conversation in real life.
Basically the earth goes through cycles of warming and cooling, and has for the past few billion years. To be sure, this is a natural process. Although the earth has never had to deal with industrialized humans before. There is no evidence to suggest that we are drastically exacerbating the problem, but this is not to say that we are not having an effect.
I plan on seeing this movie, as I believe it is important to be aware and informed. Currently the only information I have regarding global warming comes from my own lackluster and independent research, and the fact that I have been a biology major for the past three years.
Lemme do some reading, hopefully I can return to this thread with a little more to say.
In terms of resource reduction, however, I believe you are grossly overestimating the importance of the rainforests in the net effect of global warming. Also 3 acres is not as big as you think it is, and not every American eats meat everyday. I love meat, and even I don't eat it every day. In addition to all this, there is a great abundance of photosynthetic organisms on this planet - including one people never think about. Sea algae is photosynthetic, and is where most of the world's free oxygen comes from iirc. The shit is everywhere, and constantly undergoing photosynthetic reaction, producing oxygen and releasing it.
I don't think humans will ever cease to find new and interesting ways to survive. This planet could be rendered a burning husk of it's former glory and we'd still find a way to get water out of rocks.