The Ozone Layer: How We Saved the Earth from Disaster

In the early 1980s, the world was faced with a dire problem: a rapidly expanding hole in the ozone layer. The ozone layer is a protective layer in the Earth's atmosphere that absorbs most of the Sun's ultraviolet (UV) radiation, preventing it from reaching the Earth's surface where it can cause DNA damage in plants and animals.

Luckily, about 98% of the UV radiation is absorbed by ozone molecules dispersed in the stratosphere, which are continuously broken apart and reformed in this process, maintaining a delicate equilibrium. However, in the early 1970s, two chemists, Mario Molina and Sherwood Rowland, demonstrated that widely used chemicals called chlorofluorocarbons (CFCs) could upset this balance.

CFCs were developed in the 1920s by three US-based corporations as coolants for refrigerators. Unlike existing alternatives such as ammonia or methyl chloride, CFCs were non-flammable and non-toxic, making them ideal for a range of applications such as propellants, foaming agents, and fire-retardants. They soon became a multi-billion dollar per year industry and found their way into everyday items.

In the lower atmosphere, CFCs do not break down or react with other molecules. However, Molina and Rowland showed that in the stratosphere, they are broken apart by UV light, releasing chlorine atoms. These then react with ozone, destroying it faster than it can be replenished. A single chlorine atom can destroy thousands of ozone molecules before finally reacting with something else and forming a stable molecule.

Seeing the threat to their bottom line, CFC producers pushed back to discredit the scientists, even accusing them of working for the KGB. Initial estimates showed that within 60 years, CFCs could reduce ozone concentrations by 7%. However, by 1985, it became clear that ozone depletion, especially over Antarctica, was happening much faster. Scientists stationed in Antarctica noticed a massive drop in overhead ozone occurring every spring. Satellite data revealed the vast extent of these losses, and chemical tests confirmed that the cause was unquestionably CFCs.

NASA soon released visualizations that were broadcast around the world and captured public attention. If ozone depletion continued, rates of skin cancer would skyrocket, photosynthesis would be impaired, and entire ecosystems would collapse. But many politicians disagreed about what to do, weighing immediate economic concerns over long-term ones.

The fight to ban CFCs found two unlikely allies in US President Ronald Reagan and UK Prime Minister Margaret Thatcher. Despite their general opposition to government regulation, Reagan, who had undergone treatment for skin cancer, and Thatcher, who was trained as a chemist, recognized the need for immediate action. The US and UK, along with Canada, Norway, Sweden, and Finland, led calls for an international ban on CFCs.

In 1987, representatives signed the Montreal Protocol, requiring the rapid phasing out of CFCs and creating a fund to assist Global South countries in obtaining affordable, non-ozone depleting alternatives. It was later ratified by every country on Earth—the only treaty in history to achieve this. In 1995, Molina, Rowland, and their Dutch colleague Paul Crutzen, were jointly awarded the Nobel Prize in Chemistry.

As the use of CFCs declined, the ozone hole began shrinking and is predicted to disappear entirely by 2070. But we are not out of the woods yet. While the ban was a win for the climate, as CFCs are potent greenhouse gases, the alternatives that replaced them—hydrofluorocarbons (HFCs)—are too.

The world's fight against ozone depletion took a major leap forward in 1987 with the signing of the Montreal Protocol. This agreement led to a global phase-out of chlorofluorocarbons (CFCs), which were the main culprits behind the hole in the ozone layer. However, while the ban on CFCs was a success, it also created a new problem. The alternatives to CFCs - hydrofluorocarbons (HFCs) - also have a negative impact on the environment. HFCs are potent greenhouse gases that trap more heat than carbon dioxide and contribute to climate change.

To address this problem, the Kigali Amendment was added to the Montreal Protocol in 2016. This amendment called for an 85% reduction in global HFCs by 2047. If successful, this measure alone could avoid up to 0.5°C of global warming by the end of the century.