In 1987, a group of international scientists drew up the Montreal Protocol on Substances that Deplete the Ozone Layer , which came into force shortly afterwards in 197 countries. Chlorofluorocarbons (CFCs) were the first gases that the Protocol banned. Previously, they were used in industry and in consumer goods, of which hairspray is the best-known example.

Three decades the world seems to have forgotten that the ozone layer in the stratosphere is getting thinner and that there is a gap every year over Antarctica. Moreover, other environmental problems such as global warming, dying coral reefs and dying animal species are becoming increasingly larger and more complex.

Nevertheless, the Vienna Convention for the Protection of the Ozone Layer, supported by the Montreal Protocol and Convention, has borne fruit. The layer will have recovered in fifty years, right? Not quite…

"The Montreal Protocol has indeed saved the ozone layer," said David Fahey, director of the Department of Chemical Sciences at the National Oceanic and Atmospheric Administration (NOAA), and co-chair of the Scientific Evaluation Committee of the Montreal Protocol. "But we must remain vigilant. You can not just leave the ozone problem to its fate and hope that the world will make the right decisions . We will keep an eye on it. "

The recovery of the ozone layer is only a calculation, not a fait accompli. The most dangerous ozone-depleting substances are now under control, but new ones remain and we do not know what they can bring about. In the meantime it has been shown that the fate of the ozone layer is intertwined with the emission of greenhouse gases and the warming of the earth . That could lead to an unpredictable dichotomy: the ozone layer could become thinner again, or just worryingly thick. In the latter case, less ultraviolet light could reach the planet, which would drastically affect our lives, health and well-being.

How it all started

Scientists have been worrying about the ozone layer since 1974. In that year professors at the University of California, Irvine, discovered that CFCs destroy the ozone in the stratosphere . The discovery resulted in several years of debate. For example, a report from the National Chemical Society meeting in San Francisco points to disagreement between scientists and producers. Chemists believed that the ozone layer would decrease by 13% by 2000, which in the US alone would lead to 80,000 additional cases of skin cancer. The members of DuPont, the largest producer of CFCs, refuted those figures and believed that ozone levels would fall by only 0.05% .

But the scientific evidence for the ozone problems was so convincing that denial did not make sense. By the end of the 1970s, most countries had voluntarily banned the use of CFCs in aerosol cans and imposed restrictions on industry. In 1985 British scientists published that they had discovered a hole in the ozone layer over Antarctica , and the Vienna Convention for the Protection of the Ozone Layer was approved. Two years later, the subsequent Montreal protocol set concrete targets to reduce the use of CFCs.

_{Researchers at the South Pole are launching a weather balloon with an ozone probe in the context of research into the hole in the ozone layer.}

New ozonkillers, however, appeared quickly. Producers replaced the CFCs with other gases , mainly chlorofluorocarbons (HCFCs). These were sold to consumers as ozone-friendly, while they were not actually at all. The Protocol thus quickly included HCFCs in the list of harmful substances, and later also added halons, methyl bromide, carbon tetrachloride, bromochloromethane and additional CFCs such as CFC-113.

Fluorocarbons (HFCs) were the next culprits that were exposed. The popular replacement for certain banned substances turned out to be anything but innocent because of its influence on the greenhouse effect. HFCs heat the stratosphere and accelerate the chemical reactions that destroy the ozone layer. The share of HFCs in global warming could reach 20% of the share of carbon dioxide by 2050. Fortunately, regulations are coming: in 2016, the 197 member states of the Montreal Protocol have adopted an amendment to reduce the use of HFCs by more than 80% over the next thirty years. "That's a big step," says Steve Montzka, a chemist from the NOAA.

All these efforts are paying off. Data from 2014 show that the highest values ​​of ozone-depleting substances have fallen by 10-15% . Ozone levels have therefore risen, especially in the upper part of the stratosphere. "We had already expected to see the first signs of recovery there," said Susan Strahan, senior researcher at the Universities Space Research Association. According to her, it is a good sign, and if everything goes according to plan, the average global ozone content by 2050 should be at the level of the 1980s .

New chemicals are lurking

We constantly adjust chemical substances for industrial use, and that has a complex effect on the ozone layer recovery process. That is why scientists must also keep an eye on those substances.

Compounds with bromine, an element that affects ozone, are covered by these new hazardous chemicals. Because the oceans heat up and evaporate, they release more substances with bromine, which in the future can influence the ozone levels. "Bromine is very bad for ozone," says Strahan. We have to keep an eye on it. "

Dichloromethane also poses a potential threat to the ozone layer . In South Asia, it is widely used in industry, so that levels in the atmosphere have increased by 60%. It is so volatile that it is usually already broken down to reach the ozone layer, but because it is emitted so close to the equator, it rises faster. "Near the equator there is a path through which most chemicals enter the stratosphere," says Strahan, and that is why we must also follow this substance.

Then there is also the troublesome nitrous oxide (N 2 O) , nitrous oxide in the vernacular. The title of a 2009 study does not lie: Nitrous Oxide (N₂0): The Dominant Ozone-Depleting Substance Emitted in the 21st Century (Nitrous oxide (N 2 O): The main ozone depleting substance in the 21 ecentury). According to Fahey, this is an appropriate title: almost all dangerous ozone-depleting substances are already under control. "Nitrous oxide remains last," he says. "It contributes to the loss of ozone, but not on a large scale." The warming of the earth causes the middle layer of the stratosphere to become warmer, which reduces the harmfulness of nitrous oxide. This does result in an ironic side effect: if we succeed in reducing global warming, nitrous oxide is a bigger problem.

In addition, many ozone-depleting gases also contribute to global warming. In 1980 that was not a big problem, but certainly now. " When they wanted to limit the emission of ozone-depleting gases for the first time, they were not really concerned about the climate yet. But these chemicals have an important role in the generation of greenhouse gases, "says Montzka," and they do make a difference ".

According to a 2007 report, The Importance of the Montreal Protocol in Protecting Climate ("The Importance of the Montreal Protocol to the Protection of the Climate"), "the impact of climate protection that the Montreal Protocol alone has brought about is much greater than what we the first commitment period of the Kyoto protocol could ever have been achieved ". In 2017 , researchers measured this dramatic impact, and what appears to be: by reducing the emission of ozone-depleting substances in the US, the equivalent of 170 million tons of CO 2 has never ended up in the atmosphere .

Too much recovery is not good either

But that does not mean everything about the interaction between the hole in the ozone layer and the warming of the earth. As the earth, and thus also the stratosphere, heats up, greenhouse gases cause the upper stratosphere to cool down. As a result, less ozone is lost. "Here we are boiled, while that far above our head ensures that the loss is inhibited", says Strahan. But this so-called super recovery is not necessarily a good thing - it could lead to an extra thick ozone layer that would transmit much less ultraviolet light. And that could ultimately have a negative effect on all life on earth.

The size of the ozone hole above Antarctica still varies from year to year and from season to season. When the sunlight returns at the end of the winter, it activates the ozone-depleting gases in the stratosphere, accelerating the damage process by about one percent per day. But it also depends partly on the weather around the poles: because it was slightly warmer in 2017, fewer stratospheric clouds were created. That delayed the ozone-depleting chemical reactions, leaving the gap on September 11 with 'only' 19.7 million km 2 at its smallest since 1988.

So, if you thought ozone was something of the 80s, then you are wrong. The layer that protects life on earth has not yet been completely restored . Fortunately, the Montreal Protocol scientists keep an eye on things.

"I like to view the scientific assessment committee as a kind of SWAT team," says Fahey. "We identify problems and look for ways to proactively solve them".

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Thank You For Reading

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References:

1. The Montreal Protocol Is Healing Earth’s Ozone Hole

2. Saving the ozone layer: why the Montreal Protocol worked

3. Saving the Earth's Ozone Layer Went Even Better Than Expected