Over the last decade or so, more and more people have started talking about environmental issues such as global warming and climate change. Scientists have attributed this phenomenon to the depleting ozone layer among various other factors. Rapid industrialization, increasing pollution, and various other human activities caused significant damage to the ozone layer. In fact, scientists discovered a gaping hole in the protective shield over the North Pole sometime in the 80s. However, recent reports released by the United Nations have revealed that the ozone layer has started repairing itself. By the 2030s, the area over the Northern Hemisphere should heal completely. The section over Antarctica, on the other hand, maybe not be healed until the 2060s.

The ozone layer, part of Earth’s atmosphere, protects us from the Sun’s ultraviolet rays. Without it, we would be fully exposed to these harmful rays that cause crop damage, skin cancer, and eye damage.

The ozone layer, also known as the “ozone shield,” is part of the stratosphere. Compared to the other sections of Earth’s atmosphere, the ozone layer contains high levels of ozone or O₃, an inorganic molecule. Found primarily in the lower section of the stratosphere, the layer starts at about 9.3 to 21.7 miles above our planet. Geographical and seasonal changes can cause the thickness of the layer to vary.

Ozone is an extremely reactive gas, and its molecules are composed of three oxygen atoms. It absorbs the UV radiation, particularly the harmful UVB rays, that are sent to Earth from the Sun. UVB rays are known to cause damage to the marine ecosystem and agriculture. Moreover, long-term exposure to these rays can cause eye damage and skin cancer in humans. Atmospheric ozone, also known as the “good” kind, should not be confused with ground-level or tropospheric ozone which is a key element of air pollution.

In 1974, scientists discovered that the ozone layer was being damaged by CFC or chlorofluorocarbon gases. This man-made damage posed a significant threat to Earth’s atmosphere and the safety of life on the planet.

Sherwood Rowland and Mario Molina, two chemists from a California university, first published their findings in 1974. Their article detailed how chlorofluorocarbon gases were damaging the ozone shield. Back then, CFCs were primarily used in coolants (found in air conditioners and refrigerators) and aerosol sprays. When CFC gases reach the stratosphere, the UV rays break them down and produce chlorine.

The groundbreaking research, for which the scientist duo won the 1995 Nobel Prize, concluded that our atmosphere can only absorb a finite amount of chlorine. According to the U.S. Environmental Protection Agency, one chlorine atom is capable of destroying over 100,000 ozone molecules. Since ozone is already scarce in the atmosphere, the CFC gases can destroy them more rapidly than it can possibly be replaced.

In 1985, Rowland and Molina’s work found much validation when a group of English researchers found a gaping hole in Earth’s protective shield. The damage was found over Antarctica and was attributed to chlorofluorocarbon gases. This area of the stratosphere, where the “hole” was discovered, already has extremely low ozone concentrations. Between August and October, when spring occurs in the Southern Hemisphere, the sunlight produces chlorine, which causes damage to the layer.

Seeing the harmful effects of CFC and other substances on the ozone layer, the Montreal Protocol was introduced in an attempt to protect and repair the shield. After 30 years, we can see the positive effects.

After recognizing how CFC and other substances damage the ozone layer, 180 countries came together and signed the Montreal Protocol in 1987. This international treaty called “Montreal Protocol on Substances that Deplete the Ozone Layer” passed the landmark decision of phasing out the harmful substances. Without this treaty, the United States would have had an additional 280 million instances of skin cancer, 45 million cataracts, and 1.5 million deaths related to skin cancer, and Earth would be 25% hotter.

Three decades after the treaty was signed, scientists at NASA have come up with the first official proof that the ozone layer over Antarctica is healing itself. Thanks to lower CFC production and usage, ozone depletion has reduced by 20% in the area since 2005. Back in 2018, the UN revealed an assessment report that confirmed this recovery. The report also predicted that the ozone layer will continue healing itself in the coming decades. The ozone layer over the polar regions should be completely repaired by 2060.

Though the recovery has started, the road forward is not all smooth. The lower stratosphere has been experiencing reduced ozone concentrations. Reports have also revealed potential ongoing violations of the treaty.

Scientists are constantly monitoring the ozone layer, and they have found some troubling signs. A 2018 study revealed that ozone concentrations in the lower stratosphere have reduced inexplicably and unexpectedly since 1998. There are even reports of some violations of the Montreal Protocol. Coolants, which still go on today and continue to produce harmful gases.

Transitional substitutes such as HCFCs or hydrochlorofluorocarbons may be less harmful, but they still damage the ozone shield. These substances are still in use. The Multilateral Fund, which is a part of the Montreal Protocol, can provide sufficient funding to developing nations so that they can finally stop the usage of these substances. Though the next-gen coolants do not directly harm the ozone layer, they harm the planet in other ways. These greenhouse gases trap heat and add to global warming.

It is true that compared to greenhouse gases such as carbon dioxide, HFCs are much smaller in number. However, their effect on climate change cannot be ignored. That is why in 2016, the Kigali Amendment was introduced to the Montreal Protocol. The amendment came into effect in January of 2019, and it aims at reducing the usage of HFC by over 80% in the next 30 years.

As of now, scientists and companies around the world are trying to come up with more eco-friendly alternatives to these harmful substances. New coolants are being manufactured, and advanced technologies are being designed to eliminate or reduce our dependence on chemicals.

[Sources: 1, 2, 3, 4, 5]