Since their discovery in the late 1920s, chlorofluorocarbons (CFCs) had been used extensively in the production of consumer goods across the globe. CFCs were part of the ‘mid-century chemical revolution’ that brought innovations such as affordable refrigerators, air conditioning systems and aerosol cans for deodorant by the 1960s. Given their special characteristics of being inflammable and non-toxic to human beings, CFCs were very popular substances. There were 1.2 million tons of ozone-depleting substances (ODSs) (which include CFCs) being produced for consumer use in 1986. 
In 1974, British scientists Sherwood Rowland and Mario Molina discovered that CFCs rise miles up into the earth’s atmosphere when released. Once in the stratosphere , CFCs are split apart by aggressive sun light and destroy ozone molecules by releasing harmful chlorine atoms into the ozone layer. The ozone layer protects the earth from harmful UV radiation that has deadly health impacts on humans. UV radiation results in higher incidence of skin cancers and eye cataracts, more-compromised immune systems, and negative effects on watersheds, agricultural lands and forests. However, many in the public and the chemical industry at the time were very sceptical of these findings when they were first published. “If you came off the street, it seemed ludicrous that underarm deodorants might have an effect in a global way” Sherwood Rowland remembered.
By 1985 the British Antarctic Survey discovered a hole in the ozone layer over the Antarctic. Subsequently, NASA discovered that the ozone layer was thinning in densely populated areas in the northern hemisphere of the earth. The loss of ozone found was much larger than any amount that could be accounted for with already existing scientific models. These discoveries led to increased public attention and a sense of urgency that created a unique window of opportunity for global action. As a result, 20 countries signed the Vienna Convention for the Protection of the Ozone Layer in the same year. It was a multilateral environmental agreement between countries that established a framework to negotiate how to best regulate ozone-depleting substances, such as the production of CFCs. However, CFC producing giant DuPont and the Alliance for Responsible CFC Policy, remained sceptical. In a testimony before the US congress in 1987 Du Pont representatives rejected the idea that ozone depletion was an imminent crisis and concluded that the science was not yet conclusive. Former DuPont Chairman Richard D. Heckert, in a letter to the US Senate, remained convinced that “scientific evidence does not point to the need for dramatic CFC emission reductions”.
The 1985 Vienna Convention created a legal framework for countries to negotiate how to best regulate the variety of ozone depleting substances (ODS) globally. This paved the way for a more concrete international treaty under its umbrella, the Montreal Protocol. The Vienna Convention also established the Ozone Secretariat under UNEP, which oversees the Montreal Protocol implementation. Article 2b of the Vienna Convention provided the legal framework for the parties of the convention to create legislative and administrative measures.
The Montreal Protocol was opened for signature in 1987 and entered into force in 1989. Original signatories included Russia and the United States, but initially did not include many developing countries. In subsequent years the protocol succeeded in attracting the participation and support of a broad coalition of developed and developing countries. Currently, the protocol has 197 parties.
The Montreal Protocol’s aim is to address the depletion of the ozone layer that is created by releasing harmful chemicals into the atmosphere. While it does not have the authority to control all ODSs, a majority of 100 hazardous chemicals are now covered by its provisions. In very simple terms, the Montreal Protocol provided timetables for the covered ODSs to gradually phase out and eliminate production and consumption. Different conditions were applied to developing and developed countries. These are overseen by the Ozone Secretariat. 
When the Montreal Protocol entered into force in 1989, it expressed the following three aims:
- Developed countries had to begin the phase-out of CFCs in 1993, achieve a 20% reduction relative to 1986 consumption levels by 1994, and a 50% reduction by 1998.
- Developed countries had to freeze production and consumption of three halons relative to their 1986 level by 1993.
- The protocol restricted the trade of CFCs with non-parties to prevent relocation of production facilities to countries that were not signatories.  
In 1990 these original goals were revised for the first time in London to aim for a total phase-out of ODSs by 2000. The Protocol further offered special treatment to ‘developing countries’ so participation would not impede their economic development. Developing countries were granted additional time in the phase-out process and a Multilateral Fund was developed to encourage developing countries to become signatories by enabling more technical transfer and support. The Montreal Protocol has since evolved with four additional important revisions after London that included more revisions and adjustments in Copenhagen (1992), Montreal (1997), Beijing (1999), and Kigali (2016). These revisions changed phase-out targets and added hazardous chemicals to the protocol.
The public impact
The public impact of the Montreal Protocol has been far-reaching, and it is celebrated as one of the most successful international treaties ever implemented at an international scale. Overall, it helped to significantly reduce the global production, consumption and emission of ODSs (ozone depleting substances) and CFCs (chlorofluorocarbons), to start healing the ozone layer.
ODSs and CFCs reached a 98% phase-out by 2010 while the remaining 2% are hydrochlorofluorocarbons (HCFCs). HCFCs are alternatives to CFCs, which became popular substitutes in consumer products, which previously relied on CFCs. HCFCs, although still broken down in the atmosphere like CFCs, are a much smaller risk to the ozone layer, but are still potent greenhouse gases. The worldwide production of ODSs has plummeted from some 1.2 million tons in 1986 to 80,000 tons in 2006 to being nearly eliminated in 2016 at 23,000 tons. Global ODS consumption has seen a similar trend dropping from 1.3 million tons in 1986 to 86,000 tons in 2006 and 22,000 tons in 2016.
A 2018 joint assessment by the World Meteorological Organization (WMO), UNEP, the European Commission, the National Oceanic and Atmospheric Administration (NOAA) and NASA concluded that “actions taken under the Montreal Protocol have led to decreases in the atmospheric abundance of controlled ozone-depleting substances (ODSs) and the start of the recovery of stratospheric ozone”. This means that the Montreal Protocol can largely be credited with the ongoing recovery of the Antarctic ozone hole while avoiding much more severe ozone depletion in the polar regions. Further, the Montreal Protocol fostered an increase in the upper stratospheric ozone of 1–3% per decade since 2000.
In an estimate by the US Environmental Protection Agency (EPA), the ozone layer would have collapsed by 2050 without the Montreal Protocol. Accordingly, the UV index measure would have increased dramatically. This could have led to an additional 280 million estimated cases of skin cancer, 1.5 million skin cancer deaths and 45 million cataracts in the United States alone.
Written by Lisa Schaefer
Public Confidence Strong
Since the discovery of the side-effects of releasing CFCs into the atmosphere and the resulting effects of UV radiation on human health, global public opinion was galvanized.
During the mid-1970s ozone depletion became a hot public topic, whether in relation to supersonic transport; regarding the use of CFCs in refrigerators and aerosol products; or in terms of their impact on human health in general. Spray cans and their effect on human health and the environment were taken very seriously by individuals and coincided with a rapidly growing and powerful environmental movement. “The fear of skin cancer from the depletion of stratospheric ozone due to the use of CFCs as aerosol propellants in spray cans personalized the risks for many people. Through the media, the public learned that such nonessential products as aerosol hairsprays and deodorants could pose serious future environmental and health risks. The public came to view the risks of using CFC-based aerosols as unacceptable”. Especially, the rise in melanomas and glaucoma resulting from a thinner ozone layer and a higher exposure to solar radiation galvanized global public support and made protection of the ozone layer an important global health issue that was discussed in the media at length. 
Consequently, American consumers stopped buying aerosols containing CFCs at large even before an official ban of CFCs in aerosols by the US government in 1978 after US politicians felt forced to address the issue. This drastically cut the consumption of CFCs in the US for the first time and was one of the first steps to soften the industry position towards CFC regulation later on.
On the other hand, some stakeholders in Europe, specifically France and the UK, and Japan, remained sceptical. “Britain and France questioned whether the United States was being motivated by economic concerns (the threat of European dominance in commercial supersonic flight) rather than environmental concerns.”. Japan had similar concerns and also worked to protect their national producers. However, public opinion quickly shifted and environmental groups started to exert pressure on their governments while consumption of CFCs started to decline globally.
Stakeholder Engagement Strong
The Montreal Protocol represents one of the biggest collective action efforts in human history with very effective stakeholder engagement on an international scale. It managed to take into account the interests of a broad range of stakeholders, including nation states, industry groups, scientists and NGOs throughout the negotiation of the final treaty.
Before the Montreal Protocol, scientists and environmental NGOs had already started lobbying efforts to increase awareness of how ozone depletion affected the earth’s environment after the initial findings by Rowland and Molina. The scientific community at large was consulted in a consistent manner during and before the negotiations of the Montreal Protocol. Major research projects, sponsored by UNEP, EPA, WMO and other organisations helped develop a consistent scientific assessment of ozone depletion (see: Evidence). This demonstrated international consensus among policy makers, scientists and the public, that CFCs were recognized as a serious threat.
The chemical industry started to publish its own research in the 1970s, being critical of CFCs’ harmfulness. As researchers were still debating the scientific consensus at the time, industry started their own public relations campaigns, backed by industry-friendly research on a national level.  “A senior executive at DuPont, the world’s largest [CFC] producer, testified before a [US] Senate panel that the ‘chlorine-ozone hypothesis is at this time purely speculative with no concrete evidence (…) to support it.’ At the very least, industry representatives suggested no harm would come from each year’s delay and that costly regulation should not be imposed until further research had been established that real risks were involved.”  Only gradually, industry began to shift its opinion to support a phase out of CFCs in the mid-1980s.
After the discovery of the ozone hole over the Antarctic in 1985, the scientific and NGO community at large actively supported banning CFCs to protect the ozone layer. Contrarily, chemical producers, drawing on their previous experience with battling national ozone regulations, realized their economic interest in creating a global ozone regulation. They began to see economic benefit in a global even playing field for all CFCs producers. At the same time, the development of affordable CFCs substitutes globally created an incentive for chemical producers to develop a CFC alternative first. During the final stage of negotiations of the Montreal Protocol, industry had shifted from their previous position towards being supportive of regulations on a global scale. US producer DuPont had already dealt with several domestic regulations and seven public campaigns (see: Public Confidence) including a ban on aerosols. It was the first company to offer an alternative to CFCs. Therefore, the world’s largest producer also had a business opportunity to gain market share by supporting an international CFC ban. “Governments listened to business advice and actively sought to engage corporate actors in the international political process. Some industry experts even became part of the influential UNEP technology assessment panels that gave authoritative advice to governments on the technical hurdles to phasing out ODS”.  
Political Commitment Strong
The Montreal Protocol represents a political commitment by many nation states brought together under the auspices of the United Nations Environment Programme (UNEP). In terms of political commitment on the international stage, individual countries as well as groups of countries drove the development of the Montreal Protocol by drafting strategic proposals throughout the negotiation process. In general, many countries were increasingly willing to commit to address the serious environmental impact of CFCs and public health concerns the UV light was posing to their populations.
On one spectrum of the negotiating table were countries such as the Nordic countries, Canada and the US, who advocated for elimination of CFCs in non-essential aerosols. Countries within the European Economic Community (EEC) also supported the elimination of all CFCs and suggested regulations to include total use and production of all aerosols. For the US, the Ronald Reagan presidency specifically played a leading role in advocating for the Montreal Protocol and for a ban of CFCs. “Reagan convened several cabinet sessions to review and debate [the impact of CFCs on the ozone layer] and concluded that action was justified and wise. With this direction, the US played a leadership role in the negotiations that led to the formulation and implementation of the Montreal Protocol”.
On the other hand, governments from countries like Japan and the UK had a more ‘wait and see’ approach. The UK specifically, wanted to “to preserve market dominance and to avoid for as long as possible the costs of switching to alternative products”. Yet, former prime minister Margaret Thatcher, a trained chemist by trade, is said to ‘have been spooked’ by the scientific evidence of CFC impact on the ozone. 
Over time it became politically advantageous for countries to commit to the Montreal Protocol which promised improvements in environment and public health. This facilitated universal political commitment. The science-based leadership of UNEP helped, throughout the negotiation process, to bring different countries together throughout the negotiation process (see: evidence). Then UNEP Executive Director Mostafa Tolba was influential in reaching consensus via informal consultations in 1987 between the various political stakeholders. He has been credited with a concrete draft proposal that aligned control measures without demanding commitment from parties and got endorsed by more than 50 countries as the basis of the final negotiation. 
Clear Objectives Strong
The aim of the Montreal Protocol is a “phase down [of] the consumption and production of the different ODS in a stepwise manner, with different timetables for developed and developing countries”.  All parties have equal responsibilities for the control of ODS trade, annual reporting of data, national licensing systems to control ODS imports and exports, and other obligations. However, developed and developing countries have different time-targeted commitments.
The treaty has a mechanism to evolve over time in light of new scientific evidence or economic developments and continues to be adjusted. These adjustments require consent from 2/3 of the parties (a majority of both developed and developing countries). “For example, the original Montreal Protocol called for a freeze at 1986 levels for the main halons by 1993 […]. That was first adjusted in 1990 to a freeze in 1992 and a complete phase out by 2000. In 1992 it was adjusted to consumption by 1994 at 25% of 1989 levels and a complete phase out by 1996”.  Adjustments become binding on all Parties six months after they are formally notified about them.
While the original goals of the Montreal Protocol were already outlined above (see: Initiative) and have been adjusted several times, there were significant amendments made to the original protocol as well. Some of these revisions were minor adjustments and the important revisions were those on accelerating phase-out targets and adding additional chemicals. By 2000, the goals had changed from cutting production and consumption in half to a complete phase-out of certain CFCs.
- London Amendment (1990) – The protocol’s goals became much more ambitious with a decision to phase out ODSs instead of reducing their production and consumption by 50%. Achieving a phase-out has since become the common goal even when adding other ODSs to the agreement.
- Multilateral Fund (1991) – It aims to provide financial and technical assistance like industrial conversion and capacity building to assist developing countries with phase-out processes. Thus far, the Multilateral Fund has supported 8,100 projects worth US$3.3 billion.
- Montreal Amendment (2007) – Recognizing the potential benefits to the Earth’s climate, Hydrochlorofluorocarbons (HCFCs) were included in the phase out processes. Developed countries are reducing their consumption of HCFCs and will completely phase them out by 2020. Developing countries agreed to start their phase out process in 2013, aiming for completion by 2030.
- Kigali Amendment (2016)- Hydrofluorocarbons (HFCs), were introduced as non-ozone depleting alternatives to support the timely phase out of CFCs and HCFCs. However, uncontrolled growth in HFC emissions undermine efforts to keep global temperature rise at or below 2°C. The parties to the Montreal Protocol agreed to add HFCs to the list of controlled substances, and approved a timeline for their gradual reduction by 80-85% by the late 2040s. 
The effect of CFCs on the ozone layer were discovered in the 1970s by Rowland and Molina and it formed the evidence basis for the entire movement against ozone depletion. What scientists could not agree on immediately was the exact extent and effect of ozone depletion on the earth’s environment. It was not until the late 1970s and early 1980s that broad international consensus was reached on the serious threat posed by CFCs. Achieving consensus was challenging because the industry initially opposed the science by running public affairs campaigns in the 1970s to contest the academic findings as being inconclusive (see: public confidence).
However, a major breakthrough in the debate came with more scientific evidence in the form of the discovery of the ozone hole above the Antarctic in 1985, which convinced large numbers of politicians and the public of the urgency of ozone depletion.
Over time, evolving data collection and assessment methods over a decade created a stronger, evidence-based argument to develop a control mechanism for CFC pollution. Two scientific assessment projects stand out, next to the 1985 British Antarctic Survey and the WMO/UNEP Scientific Assessments of Ozone Depletion, reports published every 4 years. :
- The 1985 WMO/NASA international assessment on the processes controlling atmospheric ozone. 150 scientists from 11 countries concluded that “there is now compelling observational evidence indicating increases in the concentrations of gases which control atmospheric ozone, [… which] catalyse the destruction of ozone in the stratosphere
- The 1986 EPA/UNEP international conference and report on the effects of changes in stratospheric ozone and global climate. Followed by an international workshop in Leesburg, Virginia, which laid the groundwork for the Vienna Convention as a first draft proposal.
Taken together, these discoveries and events demonstrated broad consensus among scientists and policymakers that CFCs are threatening the ozone layer, that the problem was global in scope, and that society would have to deal with the effects.  UNEP tried early on to coordinate international research in ozone depletion during the 1970s when the Ozone Secretariat had not yet been established. It tried to monitor and study stratospheric ozone and the need for collaboration. By 1981, UNEP formed an ad hoc legal and technical working group to draft a Global Framework Convention for the Protection of the Ozone Layer. This became the “Vienna Convention for the Protection of the Ozone Layer” which formed the legal basis of the Montreal Protocol. The Montreal Protocol has continued to promote scientific evidence since its creation. The WMO/UNEP Scientific Assessment of Ozone Depletion is published every four years and monitors the progress that is being made under the agreement.
In order for the protocol’s goals to be feasible, widespread participation and compliance was necessary. Once the Montreal Protocol was opened for signature in 1987, a number of conditions needed to be met for it to enter into force in 1989 including at least eleven ratifications by countries representing two-thirds of the global consumption of CFCs and halons (based on 1986 estimates) and the ratification of the Vienna Convention. This was meant to ensure enough coverage so the protocol would be able to have the desired global impact.  By 1990, 58 parties had signed the protocol, accounting for a total of 90 per cent of global CFC use. Subsequently, the Montreal Protocol has achieved the universal ratification of 197 parties.
Furthermore, it became clear by 1986, that the industry would be able to provide alternative substances to CFCs. DuPont and other producers were already looking into developing new alternatives and chemical substitutes. The development of these substitutes, however, was motivated not only by having a substitute available or not, but also by market forces. DuPont, in fact, announced that suitable alternatives could be available within five years given the right market conditions. Thus, the development of alternatives was dependent on economic and regulatory incentives to do so. An international protocol was seen by industry as a useful mechanism for providing the necessary economic incentive to develop and market suitable alternatives”.  
The Montreal Protocol, through its compliance mechanisms, financial inducements, periodic scientific assessments, and treaty reviews, has put in place a process that has ensured continuing progress. First, countries agreed to take ‘appropriate’ but unspecified action via the Vienna Convention. Then, they jointly engaged in scientific research and the exchange of information. The new science on ozone depletion formed the basis of the Montreal Protocol, which created overarching regulatory obligations to reduce ODSs. This step-by-step approach from convention to protocol led to a robust agreement to protect the ozone layer. Taken together with the possibilities to make adjustments to the protocol in response to evolving scientific evidence (see: objectives), this makes for a flexible regime with great adaptive capacity that takes new realities into account and that does not require the renegotiation of the entire agreement.
The UNEP Ozone Secretariat (Secretariat) and the Executive Committee of the Multilateral Fund and various other subsidiary bodies working behind the scenes have played an important role for the successful implementation of the protocol through their oversight and management functions. The Secretariat, one of the sources of the protocol’s flexibility, can help with implementation by modifying the way in which its obligations are implemented. For example, the Secretariat prepares a report on implementation before each meeting of the parties. Any issues parties might have are then addressed during the party meeting or referred to other committees. The Ozone Secretariat also has a number of Assessment Panels -- Scientific, Environmental, and Technology and Economic--that negotiate issues between meetings, and advise on ozone protection details. “It allows for continuity in discussion of issues and is a less politically-charged arena in which new concerns can be raised, before subject to actual negotiation or complaint”.
Comprehensive metrics are tracked over time and are made available on the Ozone Secretariat’s website. The public data centre allows the tracking of ODS consumption in tonnes for all member countries since 1986, including details on specific ODS covered under the Protocol like CFCs, Halons, Methyl Bromide and more. Furthermore, all reports and statements are made publicly available. At the same time, assessment panels (see: Management) provide periodic assessments on scientific, environmental, and technological and economic developments. The Ozone Secretariat has published several public scientific assessments between 1989 and 20018 roughly every 4 years that measure and monitor progress. “Observations of atmospheric ozone are made by instruments on the ground and on board balloons, aircraft, and satellites”.  This coherent measurement of the decline of ozone around the globe contributed majorly to the monitoring process. For example, the 2014 assessment “was able to detect extreme ozone depletions over Antarctica in each spring and occasional large depletions in the Arctic”. 
At the same time, the Technology and Economic Assessment Panels produced yearly reports that track the progress made and reviews alternative technologies available. In addition to other ad hoc reports and assessments, the Montreal Protocol uses its measurement tools to not only track success but also to adjust its objectives based on new scientific findings or innovations.
By the time the Montreal Protocol was signed, there was strong alignment among all stakeholders including politicians, industry, scientists and the public on a global scale that everyone has a joint interest in protecting the ozone layer. The Protocol has now reached universal ratification among 197 states globally.
Even though the business community was initially reluctant to regulate and phase out CFCs, they turned around and eventually became advocates for an internationally binding ozone regime. Severe public and political pressure was put on producers such as DuPont to change their stance on CFCs. Given regulatory pressures, a negative public image and the decreasing revenue of CFCs, producers had to adjust. CFC production was no longer considered to be a viable business. In addition, the race to develop innovative chemicals that could replace CFCs and conquer a market made up of increasingly environmentally conscious consumers persuaded companies to invest into cooperating with the Montreal Protocol. “Based on [businesses’] pivotal role in directing technological change, corporations were able to influence the design and phasing of the protocol's regulatory instruments”. 
Furthermore, the Montreal Protocol made a big effort to get developing countries on board and broaden the list of signatories. Initially, developing countries were offered an extended phase-out period. Then, trade incentives were offered to states who were part of the Montreal Protocol. “States that are party to the agreement can only trade in controlled substances with those that are in the agreement. For states that did not produce ODSs but hoped to use them, joining the agreement was the obvious way to guarantee their access to these chemicals”. This meant that, for the Protocol to be successful, developing countries capable of producing ODSs had to be brought in as signatories. However, countries such as India and China were reluctant to sign from the beginning and indicated that these trade incentives were insufficient. For that reason, more funding and technology incentives were added later on via the Multilateral Fund, to provide incentives for developing countries to comply with the Montreal Protocol. This had the intended effect and countries such as China, India and Brazil joined in 1992, followed by other developing nations, making it the first universally adopted global environmental treaty.