Over the last 4.6 billion years, the Earth’s atmosphere evolved greatly. Its primordial atmosphere consisted of hydrogen, helium, ammonium, methane, sulfide, nitrogen, and carbon from volcanic eruptions. 2.4 billion years ago, photosynthetic bacteria started emerging, producing oxygen which led to the formation of ozone (represented by the symbol O3) nearly 600 million years ago.

The ozone layer, a section of the stratosphere, lies about 10 to 25 miles above the surface of the planet. To create ozone molecules, a procedure called photodissociation, in which high-energy UV light splits oxygen (O2) molecules apart by creating oxygen atoms that mix with other oxygen molecules, occurs. Chemical reactions and cosmic radiations constantly destroy and generate ozone molecules.

In the early 1900s, people needed a method to keep their food from spoiling during summer. A person called the “iceman” would come to one’s house and sell a block of ice that was kept in an icebox to preserve specific foods that get spoiled quickly. There were several flaws with this such as the frequent ice replacement. As an alternative, a gas-powered system using ammonia or sulfur dioxide as a coolant was created. However, these chemicals were toxic and would regularly leak. People needed a replacement: a coolant that would keep food warm and not exude dangerous substances. Scientists in the United States invented their own molecules to solve this problem. Specifically, Thomas Midgley, Jr invented CFCs (chlorofluorocarbons), a chemical containing atoms of carbon, chlorine, and fluorine. In 1930, at the annual meeting of the Chemical Society of Atlanta, Midgley proposed a safer, efficient way to keep food cold, using CFCs. This successful new chemical found its way into not only coolants in fridges, but also shaving cream, fire extinguishers, air conditioners, propellants in aerosol sprays, and the production of foam plastics. CFCs were deemed harmless, resulting in industry and community to be unconcerned with their global use and release into the atmosphere.

It wasn’t until the 1970s that Mario Molina, a young chemist who immigrated from Mexico, and Sherwood Rowland, a chemical kineticist, discovered the lasting negative impacts of CFCs. They hypothesized that the CFCs, considered non-toxic, didn’t magically disappear; rather, they accumulated in the trillions at the edge of space, high above the earth. Molina and Rowland simulated the chemical reactions that would occur when CFCs came in contact with UV radiation over countless lab experiments. Eventually, their research led to the discovery that UV radiation caused CFCs to release highly reactive chlorine atoms. A single chlorine atom can destroy one hundred thousand ozone molecules, causing the ozone layer to slowly diminish. In 1995, Mario J. Molina and F. Sherwood Rowland won a Nobel Prize in Chemistry for their pioneering discoveries on ozone depletion.

Ozone plays a critical function in preserving life and the fragile environmental balance of our world. The ozone layer acts as a natural barrier to block the sun's damaging ultraviolet (UV) radiation, providing protection against many harmful effects that might otherwise affect life on Earth, such as an increase in skin cancer cases, cataracts, and damage to aquatic and terrestrial ecosystems. Additionally, it absorbs and scatters UV radiations, playing an essential part in maintaining the health and well-being of living things.

Companies were not inclined to reduce the manufacturing of CFCs since they considered it crucial for the society's betterment. They responded to the discoveries by stating that the science wasn’t settled yet, looking for other causes for the loss of ozone in the sky. A worldwide outcry arose. People demanded that companies stop manufacturing CFCs.

In 1985, decades later, the Vienna Convention took place, promoting cooperation internationally and laying the framework for a global scale agreement. In 1987, the Montreal Protocol was enacted to phase out the production and use of ozone-depleting substances(ODS), one of the most successful environmental global actions and the first to achieve universal ratification by the United Nations. ODS is now largely removed from the atmosphere. The United Nations Environment Program now predicts that the ozone layer will be fully repaired by 2050.

The pressing problem of climate change now presents a more imminent threat to our planet. The rise in global temperatures and release of greenhouse gasses are threatening crops and wildlife, causing health risks and erosion that disrupts ecosystems, and generating intense natural disasters. Burning fossil fuels and cutting down trees are major reasons for climate change. Not only are oil companies denying their contribution to climate change because of the billions of dollars at stake, but they are doubling down on building capacity for non-renewable energy sources as indicated by the recent mergers in the industry. It seems that history is repeating itself.

Humankind has faced many challenges before and our ingenuity has helped us overcome such challenges. Several initiatives are considered to control and reverse climate change including switching from high carbon emitting fuels to renewable energy, such as solar power and wind power. Innovations such as carbon capture and storage technology (CCS) that capture carbon dioxide emitted from power plants and industrial facilities underground are being developed. In this ever changing and precarious world, I wonder, how old will I be when the world leaders decide to sign an accord like the “Montreal Protocol” for climate change?