Thanks for downloading analysis from the BBC. This week we bring you some good news about humanity and the planet.

As the Paris Climate Agreement comes into force and as governments prepare to meet in Morocco to discuss the way ahead,

Helena Merriman looks at one of the greatest success stories in the history of

environmental negotiations.

When Mario was little he turned his bathroom into a chemistry lab.

He'd spend hours in there, playing with tubes and potions, dreaming that one day he might

become a scientist. Sure enough he got a job in a top lab, and one day, age 30, he carried out an experiment.

An experiment that revealed something terrifying,

going on right above our heads.

In today's analysis, we're going to tell you the story of what he discovered and how it led,

eventually, to this.

Researchers say they have found the first clear evidence that the thinning in the ozone layer

above Antarctica is starting to heal.

The gains have been credited to the long-term phasing out of ozone-destroying chemicals.

In June, after years of research, scientists discovered that the hole in the ozone layer had shrunk.

The ozone layer, the only thing standing between us and deadly radiation, had begun to heal. How?

Well, it's quite a story, one that foreshadows the drama of climate change politics involving

breakthrough science, industry pushback, fears over economic chaos, and tortuous negotiations.

And it all begins here with Mario, a Nobel Prize-winning scientist.

I got interested in science when I was a child,

started playing with chemistry sets, microscopes, and so even at 11, 12 years old I became fascinated with science.

And that's Mario, now Professor Mario Molina. He's from Mexico,

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