Human beings, because we're so clever, have removed every single one of those population limiting factors... So nothing controls our increase in numbers except our own wish. Since I first started making television programs, the population of the world has increased three times. That's an extraordinary notion. Can it increase four times? Can it increase five times? The Earth is a finite size. So a point will eventually come when we run out of food, when we run out of space and when we will have destroyed most of the natural world. So ought we to do something about it before that happens?

If my grandchildren were to look at me and say, 'You were aware species were disappearing and you did nothing, you said nothing', that I think is culpable. I don't know how much more they expect me to be doing, I'd better ask them.

Clearly we could devastate the world... as far as we know, the Earth is the only place in the universe where there is life. Its continued survival now rests in our hands

I just wish the world was twice as big and half of it was still unexplored.

I have no doubt that the fundamental problem the planet faces is the enormous increase in the human population

The notion of ever more old people needing ever more young people, who will in turn grow old and need even more young people, and so on ad infinitum, is an obvious ecological Ponzi scheme.

I don't run a car, have never run a car. I could say that this is because I have this extremely tender environmentalist conscience, but the fact is I hate driving.