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The ozone layer: Earth's natural sunscreen
The ozone layer filters ~97-99% of incoming UV radiation; the Montreal Protocol is the first treaty ratified by every country on Earth.
A thin shield of ozone high above Earth filters the ultraviolet radiation that would otherwise make surface life impossible. When CFCs thinned it, every nation on Earth signed the Montreal Protocol; atmospheric monitoring now shows the layer healing on schedule, with recovery to 1980 levels projected around mid-century — proof that global environmental cooperation works.
A thin shield of ozone high above Earth protects life by filtering harmful sunlight.