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Start Whatever Happened to… the Ozone Layer Hole?
06 April 2021

Whatever Happened to… the Ozone Layer Hole?

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When researchers Frank Sherwood Rowland (June 28, 1927 – March 10, 2012) and Mario Molina (19 March 1943 – 7 October 2020) told the world in 1974 that aerosol hairsprays damaged the part of the atmosphere that protects us from solar ultraviolet radiation, the reactions were not simply disbelief: a senior chemist at DuPont called the theory a “science fiction tale,” “a load of rubbish” and “utter nonsense.” However, soon after, the so-called ozone hole became not only a global concern, but also one of the symbols of the green activism of the 1980s. The rapid reaction to tackle the problem by banning harmful compounds represents the greatest success achieved by an international environmental agreement. But it is also an example of how technological progress is seeking more sustainable solutions to the problems that technological progress itself has caused.

The success of Rowland and Molina, chemists at the University of California, Irvine, was to piece together ideas that had gone unnoticed by others. In the early 1970s, it was known that chlorine and other substances can catalyse the destruction of ozone, a compound composed of three oxygen atoms that is present in a greater proportion in a layer of the earth’s stratosphere, and which blocks much of the harmful UV radiation. However, no one had linked this phenomenon to chlorofluorocarbons (CFCs), gases that began to be produced industrially in the 1930s and were used extensively as aerosol propellants, refrigerants and to make plastic foams. CFCs are inert and long-lived, so they can remain in the atmosphere for decades. Rowland and Molina theorized that the breakdown of CFCs by sunlight releases chlorine, which could result in significant damage to the ozone layer.

Despite the initial negative reaction to the study by the two chemists, subsequent experiments and atmospheric measurements soon confirmed that they were correct. In 1985, a study by the British Antarctic Survey discovered something that surprised the scientific community, a particularly sharp decline in ozone concentration over Antarctica, when the decline was expected to be equally distributed across the planet. The following year, US National Oceanic and Atmospheric Administration (NOAA) researcher Susan Solomon provided the explanation: the cold winter temperatures at the poles form stratospheric polar clouds, which encourage the breakdown of CFCs and other halocarbons —composed of carbon and halogen elements such as chlorine, fluorine, bromine or iodine— generating more free chlorine, which in the southern spring accentuates the destruction of ozone.

The most successful environmental agreement in history

The scientific consensus on the ozone hole led some countries to adopt unilateral measures, and in 1987 a total of 46 nations signed the Montreal Protocol, aimed at phasing out the production of ozone-depleting substances. However, industry was still reluctant to throw in the towel; in 1988, DuPont’s president, Richard Heckert, wrote to the U.S. Senate: “At the moment, scientific evidence does not point to the need for dramatic CFC emission reductions. There is no available measure of the contribution of CFCs to any observed ozone change.”

The Montreal Protocol, in force since 1989, is often regarded as the most successful international environmental agreement in history. In fact, according to the UN, to date it is the only UN treaty that has been ratified by all the countries on the planet, all 197 member states. On a transitional basis, CFCs have been replaced by hydrochlorofluorocarbons (HCFCs), which are supposed to be less harmful to the ozone layer, with the aim of replacing them entirely with hydrofluorocarbons (HFCs) and other compounds. These are more unstable in the lower atmosphere, so their impact on stratospheric ozone is assumed to be low or zero. Thanks to the reduction in CFCs, in 2018 NASA showed for the first time that ozone destruction had dropped by 20% compared to 2005, and forecasts spoke of an almost complete disappearance of the Antarctic hole between 2060 and 2080.

Interactive timeline: Evolution of the Ozone Layer

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However, even if this goal is achieved, the path won’t be free of ups and downs due to seasonal cycles. In 2019, the size of the Antarctic hole reached its historic minimum, but then the austral winter of 2020 brought especially cold temperatures to the ozone layer over Antarctica, favouring the formation of the polar stratospheric clouds described by Solomon. The result was that in mid-August the hole began to grow until reaching a size of more than 24 million square kilometres in September, higher than the average over the last decade and covering most of the continent. 

The phenomenon finally subsided at the end of December, but 2020 also saw the emergence of a new worry when in March of that year a hole of unprecedented scale appeared in the Arctic, triple the size of Greenland. This opening over the North Pole, a rarer occurrence not observed since 2011, closed during April. According to experts, these variations were not related to the economic shutdown caused by the COVID-19 pandemic, but were due solely to atmospheric dynamics.

More sustainable and viable solutions

But the implications are more complex: in addition to their effect on ozone, CFCs are also much more powerful greenhouse gases than CO2. A recent study conducted by Columbia University (USA) atmospheric and climate dynamics expert Lorenzo Polvani has determined that ozone-depleting substances such as CFCs have been responsible for half of the warming of the Arctic and the melting of North Pole ice during the second half of the 20th century. “Banning of CFCs by the Montreal Protocol will mitigate Arctic warming and sea ice loss in the coming decades,” Polvani told OpenMind, although he made it clear that the overall trend will not be reversed without the necessary reductions in CO2, the main culprit in climate change.

One problem is that alternative solutions to CFCs must not only be more sustainable, but also economically viable. In 2018, a team led by NOAA researcher Stephen Montzka discovered an unexpected 25% increase in emissions of CFC-11 (the second most abundant CFC) starting from 2012, slowing the decline in the concentration of this gas by 50%, and this despite the fact that the Montreal Protocol established the cessation of global production by 2010. “We identified China as being responsible for about half of that global emissions increase,” Montzka told OpenMind.

A subsequent study has determined that the increase in CFC-11 was transient and that, according to the authors, “any substantial delay in the ozone-layer recovery has been avoided, perhaps owing to timely reporting and subsequent action by industry and government in China…” Nevertheless, it has been noted that alternatives to CFCs may be too expensive or unaffordable for some countries.

There is also another complication: ozone-friendly HFCs also contribute to climate change.  In recent years there has been an increase in emissions of HFC-23, a by-product of the manufacture of HCFC-22; this compound is the biggest cause of global warming among the HFCs and should have been drastically reduced under the current version of the Montreal Protocol. However, the discrepancy between detected and expected levels is of such magnitude that it is equivalent to the total greenhouse gas emissions of a country like Spain in one year. Most of this increase comes from China and India. In short, finding a practical way to cool ourselves and propel our aerosols without destroying the ozone layer or aggravating climate change is still an ongoing technological challenge.

Javier Yanes

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