On September 16, 1987, 196 nation-states committed to ending ozone depletion by phasing out the use of chloroflurocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). The CFC Phase-Out Management Plan is complete: CFCs can no longer be found anywhere in the commercial market. The HCFC Phase-Out Management Plan is scheduled to begin in earnest in 2013, with phasing out to be completed by 2030. Operation Sky Hole Patching has been implemented to address the problem of illegal trade in these substances.
The Montreal Protocol may be the most successful environmental treaty ever created. Thus far, the global CFC reductions have resulted in a 10% drop in the (atmospheric) effective equivalent chlorine level between the 1994 peak and 2008. This is still a drop in the bucket: yet it is enough that the ozone layer is now finally starting to stabilise. Ozone depletion has not yet stopped, but it is slowing down. A statistically significant turnaround may even be detectable by as early as 2024.
We can’t expect it to be a fast thing. The interaction between ozone (O3) and the free chlorine atoms (Cl) resulting from CFC breakdown is a self-perpetuating cycle:
Cl + O3 -> ClO + O2
ClO + O3 -> Cl + 2 O2
A single free chlorine atom keeps moving in and out of a loosely bound chlorine monoxide molecule, constantly producing stable oxygen molecules but also destroying ozone each and every time. It can keep on destroying up to 100,000 ozone molecules for as much as two years. Yet if we continue along the track established by the Montreal Protocol, we can hope for ozone levels to return to 1980 levels by around 2070: nearly eighty years of CFC-free recovery to balance out a single decade of careless CFC use.
(Back in those days, our weather forecasts did not include UV warnings; and we did not have to rely on sunscreen to protect us from our own native sun.)
It will take even longer for our ozone layer to return to its pre-CFC state. CFCs can survive intact for up to a century before they finally react with ultraviolet light to break down and, in the process, release those deadly chlorine atoms in the upper atmosphere. Some models predict that it will be a hundred and fifty years before the ozone “hole” over Antarctica ceases to exist.
Nearly all of us living today have now accepted the overwhelming evidence supporting this connection: but it took decades of research and argument to demonstrate convincingly that human-created CFCs were indeed having any kind of significant environmental impact. Frank Sherwood Rowland and Mario Molina were the first to connect the known reaction between chlorine and ozone with CFCs. Their 1974 seminal paper eventually won them the 1995 Nobel Prize for Chemistry, shared with Paul Crutzen, who had developed much of the underlying theory: but not before strong opposition by DuPont almost quashed follow-up research. The findings were commonly dismissed as utter nonsense. At one point, Rowland nearly lost his job over his public statements.
Even then, the primary argument against the link between CFCs and atmospheric ozone loss was that natural sources of clorine far outweighed any human effect. It is true that natural sources of tropospheric chlorine are as much as five times greater than manmade sources. Yet for the ozone layer, only stratospheric chlorine levels matter: and there the reverse is true, since the levels of stratospheric chlorine depend on the kinds of long-lived chlorine compounds not seen in nature. The only stratospheric halocarbon which has a predominantly natural source is methyl chloride: and it is responsible only for 20% of all stratospheric chlorine. The hydrogen chloride ejected by volcanoes can produce charged chlorine ions in stable solution with water (hydrochloric acid): which cannot interact with ozone.
Another argument popularised by DuPont in the 1970s and still popular in some circles today draws on the fact that there is also a natural thinning of the ozone layer of about 30% over magnetic polar regions which recurs annually. The existence of the natural polar ozone cycle was first observed in the Antarctic by G.M.B.Dobson in 1956.
This natural cycle should not be confused with the ozone thinning caused by CFC-sourced stratospheric chlorine. In the natural cycle, ozone levels fall gradually during the winter, when there is no sunlight, and begin rising again in spring when the polar vortex collapses. The CFC-linked depletion observed later has a completely different pattern: the greatest depletion of ozone happens in the spring, shortly after sunrise – and it is not gradual, but quite abrupt. This happens because during the sunless winter, free chlorine atoms and chlorine monoxide are able to pool within polar stratospheric clouds, which can exist only in polar winter. In the spring, the clouds dissipate, releasing the free chlorine to interact with the sunlight and the ozone. As a result, already-low winter ozone levels are halved.
Faced with this kind of spin at any other time, the CFC-caused ozone depletion might easily have been dismissed altogether; and the Montreal Protocol might never have come to be.
Yet the 1970s was also a time when many environmental skeletons were beginning to surface, even against strong scientific, economic, and political opposition: a growing awareness that would culminate in the 1980 creation of Superfund sites. The DDT environmental hazards, known since the 1940s, had been made public and popular knowledge through Rachel Carson’s 1962 book Silent Spring: but the book only put into words and reasons the declines in bald eagle and peregrine falcon populations that people had been starting to see for themselves. Although the Love Canal debaucle was yet to surface, people could see the high incidence of birth defects and illnesses in the region for themselves. At the same time, the 1974 Watergate scandal shook the public’s faith in beneficent authority.
When their paper came out, Rowland and Molina were taken seriously enough that they were invited to testify before the United States House of Representatives in December 1974: which led to public funding to examine the findings. The essential validity of the hypothesis was confirmed by the United States National Academy of Sciences in 1976. Related research continued for most of the next decade: fought at every step by DuPont.
Possibly it might have stayed there, even with all the growing evidence showing a clear and growing danger. After all, the ozone layer is a long way away; and long-term solutions are never politically popular. As long as it was still functioning, the problem was not immediate, not the way a Soviet invasion of Afghanistan was, let alone a new theocracy and the national shock of the United States embassy in Iran being taken hostage. Jimmy Carter was out. Reaganomics was in.
In 1985, the British Antarctic Survey discovered the first “hole” in the ozone layer over Antarctica. Shortly afterward, a second hole was discovered near the north magnetic pole – which placed it over inhabited land.
Even then, after most of the major CFC-producing nations had recognised the sudden immediacy of the problem and signed the Vienna Convention (the immediate precursor of the Montreal Protocol), DuPont was still running a public relations campaign of resistance. Again, the language coming from DuPont’s Alliance for Responsible CFC Policy might seem very familiar: the science was still “too uncertain” to justify any change in policy. As late as 1987, DuPont representatives testified before the United States Congress that there was “no immediate crisis that demands unilateral regulation.”
Fortunately for the future of our ozone layer, the various governments of the world decided to set aside ideology and DuPont spin alike and examine at the scientific evidence objectively. The result was the Montreal Protocol. The healing of the ozone layer will be slow and even now a very few nations of the world are determined holdouts: but the steps have been set in motion. Most importantly, the global will is there. After all, we now know our future survival on the surface of the earth depends on it.