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

Now, I find that very difficult to reconcile with notions about a merciful God.

Can a growing human population still leave space for wildlife?

I don't think whole populations are villainous, but Americans are just extraordinarily unaware of all kinds of things. If you live in the middle of that vast continent, with apparently everything your heart could wish for just because you were born there, then why worry? [...] If people lose knowledge, sympathy and understanding of the natural world, they're going to mistreat it and will not ask their politicians to care for it.

The truth is: the natural world is changing. And we are totally dependent on that world. It provides our food, water and air. It is the most precious thing we have and we need to defend it.

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?

Being in touch with the natural world is crucial.