Terrorism is an immediate problem that people are very concerned about, and I am as concerned about that as anyone else. But it isn't an either or situation.

It's coming home to roost over the next 50 years or so. It's not just climate change; it's sheer space, places to grow food for this enormous horde. Either we limit our population growth or the natural world will do it for us, and the natural world is doing it for us right now.

I'm against this huge globalisation on the basis of economic advantage.

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?

No one will protect what they don't care about, and no one will care about what they have never experienced.

All our environmental problems become easier to solve with fewer people and harder - and ultimately impossible to solve - with ever more people.

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.