In 1985 British scientist Jonathan Shanklin and colleagues published a study that shocked the world. The study revealed a hole in the Earth’s atmosphere right over Antarctica. It had been caused over time by chemicals known as CFCs, used in things like fridges, air conditioning units and aerosol cans. These were destroying the layer of ozone in the stratosphere which protects us from most of the sun's ultraviolet radiation - without it, cases of skin cancer would soar. Less than two years after the discovery, world leaders signed an agreement called the Montreal Protocol, committing to phase out CFCs. It has been described as the most successful international treaty of all time - every UN country has signed up, and ozone is expected to return to its previous levels around the middle of the century.