In the 1970s Molina and Rowland realised that CFCs could reach the stratosphere, where the sun would break them apart, releasing reactive chlorine radicals that would attack ozone. Ozone in the stratosphere plays a key role, blocking ultraviolet rays (UV) from the sun.
Without sufficient ozone in the stratosphere, dangerous amounts of UV could reach the earth’s surface, damaging plants and causing skin cancer. In the mid-1980s alarmingly low levels of ozone were discovered in the stratosphere over Antarctica. Mario Molina, together with his then wife Luisa Molina, provided the winning explanation of what caused the Antarctic Ozone Hole.
In 1987 the world’s nations signed the Montreal Protocol on Substances that Deplete the Ozone Layer, agreeing to a rapid phasing out of CFCs and similar gases. In the decades that followed, the stratospheric ozone layer has repaired itself.
The Montreal Protocol is still considered to be one of the most successful international environmental agreements. Driven by scientific results showing that the world was heading in a dangerous direction, world leaders came together to remove from use the substances that were responsible. The Montreal Protocol is seen as a model, or at least an inspiration, for dealing with greenhouse gases that are driving global climate change.