I just assumed it was a metaphor for runaway climate change, which they didn't want to spell out because of the political noise it'd generate. Just like in Matrix I assumed that the nonsensical "humans as energy source" was a metaphor for "humans as coprocessors."

Basically if there's an easy way to change the explanations so the movie makes more sense to scientists, but it would have made less sense to much of the general audience, I just cut them some slack.