A gaping hole in the layer was discovered by scientists in 1985. Just two years later, the Montreal Protocol was signed - with 46 countries promising to phase out the harmful chemicals.

The deal later became the first UN treaty to achieve universal ratification, and almost 99% of banned ozone-depleting substances have now been phased out.

The Antarctic ozone hole continued expanding until 2000, after which its area and depth began improving slowly.

Now, a report co-produced by UN, US and EU agencies says the Montreal Protocol is working as hoped.

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