Science always uses metaphor.
The tropical rain forests are a telling example. Once cut down, they rarely recover. Rainfall drops, deserts spread, the climate warms.
Humans are too stupid to prevent climate change from radically impacting on our lives over the coming decades.
The world has not warmed up very much since the millennium.
You mustn't take what I say as gospel because no one can second-guess the future.
A billion could live off the earth; 6 billion living as we do is far too many, and you run out of planet in no time.