What happened to the hole in the Ozone layer?

The 1980s were a time of great concern for the world, as a rapidly expanding hole in the ozone layer threatened life on Earth. The ozone layer, composed of ozone molecules dispersed in the stratosphere, absorbs about 98% of the Sun’s ultraviolet radiation, protecting plant and animal DNA from damage. However, two chemists, Mario Molina and Sherwood Rowland, discovered in the early 1970s that widely used chemicals called chlorofluorocarbons, or CFCs, could upset the delicate balance of the ozone layer.

CFCs were developed in the 1920s by US-based corporations as coolants for refrigerators. They were non-flammable, non-toxic, and made great propellants, foaming agents, and fire-retardants, making them a multi-billion dollar per year industry. However, Molina and Rowland demonstrated that in the stratosphere, CFCs are broken apart by UV light, releasing chlorine atoms that 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.

Despite initial estimates that CFCs could reduce ozone concentrations by 7% within 60 years, it became clear by 1985 that ozone depletion, especially over Antarctica, was happening much faster. Here, the extremely cold temperatures and unique structure of Antarctic clouds accelerated ozone loss. 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 released visualizations of the ozone hole, which were broadcast around the world and captured public attention. If ozone depletion continued, rates of skin cancer would skyrocket, and global agricultural production would plummet, making plants less productive and more susceptible to disease. Entire ecosystems would collapse, and the future of life on Earth was at stake. However, 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 and Thatcher 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. The Montreal Protocol was later ratified by every country on Earth, making it 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. However, the alternatives that replaced CFCs – hydrofluorocarbons, or HFCs – are also potent greenhouse gases and are contributing to climate change. While generally less potent than CFCs, HFCs still trap more heat than carbon dioxide.

In 2016, the Kigali Amendment was added to the Montreal Protocol, calling for an 85% cut in global HFCs by 2047. This alone could avoid up to 0.5°C of global warming by the end of the century. Today, as the world faces the existential threat of climate change, the Montreal Protocol serves as a model for decisive global cooperation needed to combat it. The question is, what will it take for us to come together again?

The Montreal Protocol is a remarkable achievement that demonstrates the power of science, international cooperation, and policy-making to address pressing environmental problems. As the world continues to grapple with climate change and other environmental challenges, the lessons of the Montreal Protocol remain as relevant and important as ever.