One of the greatest environmental success stories on a global scale stemmed from careful observations by two scientists, Sherwood Rowland and Mario Molina, beginning in 1974. They studied chemical reactions caused by sunlight interacting with synthetic refrigerants known as CFCs (chlorofluorocarbons) that were thought to be harmless. But when these gases reach the stratosphere, they act as catalysts and speed up the destruction of ozone (O₃), a chemical that protects life on earth from harmful radiation. Each chlorine atom from dissociated CFC molecules can destroy up to 100,000 molecules of ozone. Hundreds of thousands of humans would experience more skin cancer and cataracts with just a 10% loss of ozone worldwide.