Welcome to the documentary from the BBC World Service.

I'm Ben Henderson, one of the presenters of Witness History,

the daily podcast that takes you back to a big moment in history,

brought to life by incredible archive and the memories of someone who was there at the time.

This is a special episode to mark Earth Day this month,

and we've brought together some of the

highlights of our show, looking back at a few of the key discoveries, setbacks and

struggles in the movement to protect the natural environment.

Let's begin in 1972, in Stockholm, Sweden, the site of the first international conference

tasked with addressing humanity's damage to the environment.

Morris Strong, who organized the gathering, speaks to Claire Bowes about why it was so difficult

to get the countries of the world to agree on change. With all the evidence that we've amassed

in our preparations for the Stockholm Conference, including the views of many of the world's leading scientists,

I am convinced that the profits of doom have got to be taken seriously.

In other words, doomsday is a possibility.

I'm equally convinced that doomsday is not inevitable.

It has become apparent that today man's own activities have reached the scale where they are the principal determinants of his own future.

Morris Strong is an unlikely champion of the environment.

A Canadian entrepreneur and politician, he'd spent his early life making money in oil and gas.

But as a young boy, he'd nurtured two passions, for nature and for the newly created United Nations.

In his late teens, he ran away to the far north of Canada and worked for the Hudson Bay Company, which was built on the fur trade.

There, he came into close contact with the Inuit people, developing respect for their relationship with nature

...