You'll discover in countries where women have control over their own bodies, where they have education, where they have birth control, where they have facilities and where they are literate, when those things happen, the birth rate falls.

I've never actually met one in the wild, but I have seen a king cobra. They go towards people, they rear up six feet tall and they're very aggressive and they are very fast. And one bite means certain death. So if I encountered a king cobra in the wild I would be very alarmed.

It seems to me that the natural world is the greatest source of excitement; the greatest source of visual beauty; the greatest source of intellectual interest. It is the greatest source of so much in life that makes life worth living.

I would be absolutely astounded if population growth and industrialisation and all the stuff we are pumping into the atmosphere hadn't changed the climatic balance. Of course it has. There is no valid argument for denial.

The future of life on earth depends on our ability to take action. Many individuals are doing what they can, but real success can only come if there's a change in our societies and our economics and in our politics. I've been lucky in my lifetime to see some of the greatest spectacles that the natural world has to offer. Surely we have a responsibility to leave for future generations a planet that is healthy, inhabitable by all species

We keep putting on programmes about famine in Ethiopia; that’s what’s happening. Too many people there. They can’t support themselves — and it’s not an inhuman thing to say. It’s the case. Until humanity manages to sort itself out and get a coordinated view about the planet it’s going to get worse and worse.

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?