Humanity is facing a very big, slow, long, drawn-out threat, and that is to do with the way the weather is changing and the size of the population.

I can mention many moments that were unforgettable and revelatory. But the most single revelatory three minutes was the first time I put on scuba gear and dived on a coral reef. It's just the unbelievable fact that you can move in three dimensions.

There's a small worm called Loa Loa Filariasis. This parasite can survive in one environment exclusively- namely, underneath the skin and inside the eyes of human beings. Children and the elderly in tropical regions (usually the poorest) are the most widely affected. A painful, slow death is virtually certain. The worm can actually live in the host for 17 years before the host finally dies.

In the West, that's what's happening. The birth rate has been dropping steadily and still is. But there is still a vast amount of the world where that's not the case. And that is where the big population growth is taking place.

Many individuals are doing what they can. But real success can only come if there is a change in our societies and in our economics and in our politics.

Until humanity manages to sort itself out and get a co-ordinated view about the planet, it's going to get worse and worse.

Birds are the most popular group in the animal kingdom. We feed them and tame them and think we know them. And yet they inhabit a world which is really rather mysterious.