Global Warming: Lessons from Ozone Depletion

Art Hobson

This article is reprinted from The Physics Teacher, with permission.

My teaching and textbook have always covered many physics-related social issues, including stratospheric ozone depletion and global warming [1]. The ozone saga is an inspiring good-news story that’s instructive for solving the similar but bigger problem of global warming. Thus, as soon as students in my physics literacy course at the University of Arkansas have developed a conceptual understanding of energy and of electromagnetism including the electromagnetic spectrum, I devote a lecture (and a textbook section) to ozone depletion, and another lecture (and section) to global warming. Humankind came together in 1986 and quickly solved, to the extent that humans can solve it, ozone depletion. We could do the same with global warming, but we haven’t and as yet there’s no sign that we will. The parallel between the ozone and global warming cases, and the difference in outcomes, are striking and instructive.

The ozone story begins in 1928 when the General Motors Corporation first synthesized chlorofluorocarbon (CFC) chemicals [2]. Being chemically inert, nontoxic, non-corrosive, nonflammable, and gaseous at atmospheric pressures but liquid at high pressures, these compounds of chlorine, fluorine, and carbon made perfect refrigerants and other products. By 1986, CFCs were a $700 billion (annually, in today’s dollars) industry for the production of Freon, aerosol spray propellants, plastic foam blowing agents, and solvent cleansers for electronic equipment. The post-World-War-II U.S. air-conditioning revolution that moved much of our population from the northeast to the southwest was based on CFCs.

CFCs created lots of business and little fuss until 1974, when scientists began asking where all these inert gas molecules might be drifting. Being inert, essentially all the CFCs manufactured since 1928 should still be in the atmosphere. But where? And what became of them there? During decades of profitable production, nobody had thought to ask.

In 1974, University of California-Irivine chemists Mario Molina and Sherwood Roland hypothesized, based only on theories and laboratory experiments and not on atmospheric measurements, that CFCs could remain in the atmosphere for decades, slowly drifting upward until reaching the stratosphere 10 to 50 km overhead. At that altitude, high-energy solar ultraviolet radiation should eventually split CFC molecules apart, releasing chlorine into the stratosphere. Chlorine reacts strongly with ozone, O3, to form ClO and O2. In the stratosphere, ClO would then be bombarded by ultraviolet radiation to release the chlorine, which would then be free to destroy another O3 molecule. In this way, each chlorine atom destroys about 100,000 ozone molecules. This could be a disaster. Because ozone shields Earth’s surface from most of the sun’s high-energy ultraviolet radiation, humans and most other life could not survive without it.

This set off an international debate, analogous to today’s global warming debate. Environmentalists argued for a protective CFC ban in order to be safe rather than sorry, while industry argued that the science was uncertain and a ban would cost money and jobs. In further analogy to the global warming debate, developing nations argued that they should be exempt from CFC restrictions because the problem had been caused by industrialized nations and the underdeveloped nations had not yet had time to benefit from CFCs. In 1978, a consumer boycott led to a U.S. ban on CFC spray-can propellants, but other CFC applications persisted, as did the debate.

Early in 1986, a comprehensive year-long international scientific study involving 150 scientists from many nations concluded that CFCs and related substances in the atmosphere had doubled since 1973 and could pose a real threat. This study was analogous to the reports of the Intergovernmental Panel on Climate Change (IPCC) that have now appeared four times since 1990. But unlike the IPCC reports, and despite the lack of direct atmospheric evidence of harm to atmospheric ozone, industry took this report quite seriously. In September 1986, after 12 years of opposition to CFC restrictions, an alliance of 500 U.S. CFC producer and user companies unexpectedly issued a statement supporting international regulation of CFCs. The industry group’s chair stated that the scientific assessment had changed industry’s evaluation and that “large future increases in CFCs would be unacceptable to future generations.” This announcement was greeted with consternation by European CFC users and producers.

Following this U.S. industry turnaround, things changed almost instantaneously. Environmentalists, scientists, the United Nations Environmental Program (UNEP), the Reagan administration, a U.S.-led international coalition of nations, and the U.S. chemical industry led by the Dow and Du Pont Corporations, took unified, strong, and swift action. Between December 1986 and September 1987 four rounds of UNEP-sponsored conferences drew up the world’s first international environmental treaty, the Montreal Protocol. The treaty took effect on 1 January 1989 with ratifications from nations representing 83% of global CFC consumption.

This remarkable treaty transformed a nearly trillion dollar international industry by mandating the complete abolition of CFCs and several related chemicals by year 2000. Furthermore, the treaty granted China, India, and other developing nations an extra ten-year grace period to produce and consume CFCs, and mandated financial and technical assistance to underdeveloped nations to compensate them for their missed opportunity to benefit from the decades of CFC use that industrialized nations had enjoyed.

Today it might seem surprising that large business interests and the conservative Reagan administration cooperated with scientists and environmentalists to draw up and approve such a treaty, especially in the absence of direct evidence of harm to stratospheric ozone. It’s a good thing they did. Even with the treaty, the U.S. Environmental Protection Agency (EPA) estimates that 200,000 Americans have died or will die from skin cancers associated with excess ultraviolet radiation brought about by CFC-caused ozone destruction.

Surprisingly, the discovery of the “ozone hole”--a large region of depleted stratospheric ozone over Antarctica--had no effect on the Montreal negotiations or the Montreal Protocol, although it did have an effect on later supplements to the Protocol. A British Antarctic survey team under Joseph Farman published the first report of the ozone hole in 1985. Susan Solomon followed this up with the first U.S. National Ozone Expedition in 1986, confirming the ozone hole’s existence and announcing evidence that CFCs were the cause. But there was little scientific consensus about any of this until six months after a second U.S. expedition in September 1987, and the perplexing and controversial new discoveries had no effect on the Montreal negotiations [2]. It is remarkable that this prescient treaty was drawn up based primarily on laboratory experiments and chemical theories, in the absence of clear and direct evidence of what was happening in the atmosphere. Somehow, the world managed to agree on a strong treaty based of possibility of harm, even though the science was highly uncertain.

We now know that, without the treaty, ozone depletion would have been much worse by now, with millions contracting skin cancer, glaucoma, and other diseases. The atmospheric concentration of the destructive element, chlorine, recently leveled off at about 4 parts per billion and is expected to decline to the supposedly safe level of 2 ppb by 2050. Notice that chlorine is measured in parts per billion, yet it was putting the planet at risk. The atmosphere is surprisingly complex and delicate. Without the Montreal Protocol, chlorine concentrations would have soared to over 13 ppb by 2010. In recognition of their contribution to the Ozone Treaty, Molina and Rowland, along with Paul Crutzen, who did similar work dealing with nitrogen compounds rather than CFCs, received the 1995 Nobel Prize for Chemistry for having “contributed to our salvation from a global environmental problem that could have catastrophic consequences.”

Within the Reagan administration, conservative ideologues such as Secretary of the Interior Donald Hodel debated this issue with realists such as Deputy Assistant Secretary of State for Environmental Affairs Richard Benedick. Luckily, the realists won. Benedick was the chief U.S. negotiator of the treaty.

In his excellent book Ozone Diplomacy recounting the story of ozone protection, Richard Benedick lists several reasons for success [2]. First and foremost was the indispensable role of science. In addition to theories and discoveries, the best scientists and the most advanced technology had to be brought together to build an international scientific consensus. Close collaboration between scientists and government was crucial. Scientists had to assume shared responsibility for the policy implications of their findings. The implication for today, when there are so many science-related social issues, is that scientists should devote more of their attention to such interdisciplinary issues as global warming, nuclear weapons proliferation, harmful pseudoscience, energy efficiency, etc.

Second, a scientifically well-informed public was a prerequisite to mobilizing the political will of governments and industry. The media played a vital role in bringing the issue before the public. Both the UN and the U.S. government undertook public education campaigns. The implication for educators is obvious: In our science courses, we need to teach the related social implications.

Third, the UNEP was indispensable in mobilizing data, informing public opinion, bringing governments to the bargaining table, and providing an objective international forum. The implication is that international scientific and environmental organizations, including the non-governmental organizations (NGOs), are crucial to solving global science-related social problems, and deserve our support.

Fourth, U.S. leadership made a major difference. The U.S. government set a good example by being the first to take action against CFCs. It developed a global plan for protecting stratospheric ozone and campaigned tenaciously for it. The EPA labored tirelessly to develop analyses of all aspects of the problem. The U.S. Department of State capitalized on the expertise of the EPA and the National Aeronautics and Space Administration. The implication is that a powerful nation, or perhaps a group nations such as the European Union, is needed to help lead the way on international environmental issues.

Why did Dow, Du Pont, and other companies begin to support CFC restrictions in 1986, despite their 12-year history of opposition to regulation? First, the chemical industry was sophisticated enough to understand and take seriously the scientific realities expressed in the 1986 international scientific study. Second, they had the good business sense to see that their interest lay not in continuing to fight the science but rather in joining the scientific realists to ban CFCs. They knew that refrigerants, spray propellants, and such would always be in demand, and that Dow and Du Pont could be leaders in developing the new ozone-friendly versions of these chemicals.

Today, the evidence that global warming is a looming catastrophe caused by fossil fuels is far more compelling than was the 1986 evidence that ozone depletion was a looming catastrophe caused by CFCs. The global warming evidence was compelling at least by the time of the IPCC’s Third Assessment Report (TAR) in 2001, which stated for example that “the current rate of [CO2] increase is unprecedented during at least the past 20,000 years,” that “there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities,” and that “temperature increases are projected to increase by 1.4 to 5.8oC over the period 1990 to 2100 [3].” In view of the 33oC natural greenhouse effect, and the 40% anthropogenic increase in CO2 (the second most important greenhouse gas, after H2O) since 1800, it is almost a no-brainer to conclude that temperatures should have increased by a few degrees due to human activities [4]. Yet the fossil fuel industry, the automobile industry, and others continue fighting tooth and nail against responsible action.

During 1989 to 2002, for example, industry sponsored an anti-scientific campaign known as the Global Climate Coalition to persuade congress and all Americans that global warming was non-existent. These forces dominated the Bush administration during 2000 to 2008, which worked consistently to misrepresent and disregard global warming science [5]. Today, Congress is barely able to pass any legislation, no matter how weak, to regulate carbon dioxide emissions.

In analogy with the ozone campaign in 1986, one might expect that the U.S. would lead the international effort against global warming. But far from leading, we have refused for 8 years to join other industrialized nations in this effort.

In analogy with the ozone campaign, one might expect that the fossil fuel industry would take seriously the excellent science of the four IPCC reports and recognize that its interest lies in accepting the science of global warming and joining in regulating greenhouse gas emissions. After all, people will continue to need energy services, and there will be plenty of business opportunity in switching from fossil fuels to efficiency, renewable energy sources, nuclear power, and in sequestering carbon dioxide emissions. But the fossil fuel industries have not really embraced these options, and have fought realistic steps to restrict greenhouse gas emissions.

In analogy with the ozone campaign, one might expect that the United States would be willing to grant the developing nations leeway in reducing their emissions, in recognition that they have not had the two centuries we have had to take advantage of fossil fuels, and that their current per capita emissions are far lower than ours. Yet many in the U.S. congress ignore these arguments, insisting that developing nations be subject to the same total national percentage emissions reductions as the industrialized nations.

Progress against global warming will continue to be impossible without the kind of cooperation from the fossil fuel industry that the world had from the chemical industry in fighting ozone depletion. Will that cooperation be forthcoming? Some would say that Earth hangs in the balance.


[1] Art Hobson, Physics: Concepts & Connections (Pearson Addison-Wesley, New York, 5th edition 2010).

[2] Throughout this article, all details concerning the history of the negotiations over stratospheric ozone depletion come from Richard Benedick’s wonderful and highly recommended account Ozone Diplomacy (Harvard University Press, Cambridge, Massachusetts, 1991).

[3] The quotations are from the TAR’s “Summary for Policymakers,” available at

[4] Art Hobson, “The plausibility of global warming,” Phys. Teach., accepted for publication.

[5] See, for example, the Union of Concerned Scientists’ Survey of Federal Climate Scientists (2006)

Art Hobson, Professor Emeritus of Physics
University of Arkansas, Fayetteville

This contribution has not been peer refereed. It represents solely the view(s) of the author(s) and not necessarily the views of APS.