The History of Ozone Holes

The appearance of ozone holes results from human activity, but their disappearance is also directly linked to human efforts. This marks the first and, so far, only successful example of global cooperation between scientists and politicians in addressing a major geo-ecological issue. Serious Science explains how it all unfolded.

The ozone layer was discovered in the early 20th century. It lies about 10-50 km above the Earth’s surface and protects the planet from harmful ultraviolet radiation. Ozone holes are regions with significantly reduced ozone concentrations in the stratosphere, allowing increased ultraviolet-B radiation to reach Earth. The story of ozone holes begins with the invention of chlorofluorocarbons (CFCs) in 1928 by chemist Thomas Midgley and his colleagues at General Motors.

CFCs were initially used in refrigeration as a cooling agent. This was an innovation, as CFCs were low toxicity, non-flammable, and had suitable boiling points for effective cooling. Before this discovery, ammonia (NH3), methyl chloride (CH3Cl), and sulfur dioxide (SO2) were used in refrigerators. Ammonia, for example, could cause poisoning if leaked, while methyl chloride posed an explosion risk. Later, CFCs were adopted not only for refrigerators but also for air conditioners and aerosol cans for dispersing products like deodorants, paints, and insecticides, as the substance provided stable pressure and fine-particle spraying of contents.

Neither scientists nor industry representatives were aware of the harmful effects of CFCs. The discovery of ozone holes happened by chance through a laboratory experiment. It turned out that when CFCs enter the atmosphere, they rise into the stratosphere, where, under ultraviolet radiation, they break down, releasing chlorine atoms. In turn, chlorine destroys ozone molecules, creating ozone holes. Depletion of the ozone layer is dangerous as it leads to increased skin cancer and cataracts, damages marine ecosystems, and affects crops.

However, this accidental laboratory discovery needed to be confirmed under real-world conditions. To this end, NASA launched a satellite in 1979 which detected ozone depletion, though on a moderate scale. The ozone layer had thinned by a fraction of 2 to 6%. These data supported the theory proposed by Molina and Rowland but needed to be more for global action. Ozone depletion was not yet catastrophic and could be attributed to natural fluctuations. Establishing a direct link between CFC use and ozone layer destruction was essential.

In 1985, British scientists published a groundbreaking paper describing the presence of an ozone hole over the Halley Bay station in Antarctica. This hole wasn’t constant; it appeared each spring in the Southern Hemisphere, during which ozone levels dropped by 40%. This discovery became a turning point, as the scale of destruction was now evident.

Nevertheless, the industry yielded slowly and was not ready to give up a profitable product. In 1986, the Alliance for Responsible CFC Policy (an association founded by DuPont) continued to argue that the science was too uncertain to justify any decisive actions. In 1987, DuPont testified before the U.S. Congress, stating, “We believe there is no imminent crisis that requires unilateral regulation.”

A unique geo-ecological experiment was conducted in the same year: two planes were flown into the stratosphere. The experiment involved 150 scientists, some on board the aircraft and others supporting the project from the ground. The results of this flight made it clear that the ozone layer was indeed being depleted due to chlorine. The scientists determined this simply yet brilliantly: chlorine levels were low as the planes approached the hole — meaning it was in a bonded state — while ozone levels were high. Within the ozone hole, chlorine levels spiked, indicating chlorine monoxide in a free state, while ozone levels sharply declined.

Yet, even this wasn’t enough to sway the industry. In 1988, DuPont’s chairman, Richard E. Heckert, stated, “We will not manufacture a product if it cannot be made, used, handled, and disposed of safely and in line with appropriate safety, health, and environmental quality criteria. Current scientific data do not indicate a need for drastic reductions in CFC emissions. No available data show CFCs’ contribution to any observed ozone changes…”

But in this story, the collaboration between scientists and responsible policymakers triumphed over industry scepticism. In 1987, the Montreal Protocol — an international agreement to reduce the production and consumption of ozone-depleting substances — was adopted and took effect in 1989. Most nations signed it; by 2024, the deal is supported by 197 countries. A fund was created to help developing countries by providing financial and technical assistance to transition to safer CFC alternatives. Research indicates that the ozone layer is recovering thanks to these measures. For example, a full recovery over Antarctica is expected in the second half of the 21st century.

The Montreal Protocol is a rare example of a successful international agreement that laid the foundation for addressing a global environmental issue. Mario Molina, who devised the laboratory experiment with a stratosphere model, reflected years later: “It’s not easy to explain to the public that certain invisible gases affect an invisible layer, which, in turn, protects us from invisible radiation. These are not obvious or widely understood concepts. But in the end, we succeeded in most countries around the world.” UN Secretary-General Kofi Annan (1997–2006) viewed it as “perhaps the single most successful international agreement.”

Today, the world is acutely aware of global warming, plastic waste accumulation, and other impending catastrophes. This successful example of international cooperation and tangible results fosters cautious optimism. Perhaps collaboration between science and policy will continue to tackle dangerous anthropogenic factors in the future, ideally before humanity crosses any “point of no return.”