The Montreal Protocol

We look at the background of the Montreal Protocol (the discovery of the ozone hole and the Rowland-Molina Hypothesis), as well as its timetable and health benefits. We also describe the various ozone-depleting substances (ODS) and chlorofluorocarbons (CFCs).
Ozone Hole: What it looks like today
The ozone hole Oct 2019 is the smallest on record, says NASA.

The Montreal Protocol on Substances That Deplete the Ozone Layer (1987) is a global agreement to safeguard the ozone layer, by phasing out the use of certain synthetic compounds that damage ozone molecules in the lower stratosphere. This landmark treaty – a protocol to the Vienna Convention (1985) – regulates the manufacture and use of about 100 ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs).

The ozone layer shields Planet Earth from harmful ultraviolet radiation that can causes skin cancer and cataracts, as well as damage to crops and marine ecosystems.

Adopted on 16 September 1987, the treaty has since undergone five important revisions which were agreed in London (1990), Copenhagen (1992), Montreal (1997), Beijing (1999) and Kigali (2016). 1 2

The treaty will continue to be adjusted in light of new scientific developments. Meantime, governance of the treaty rests with the Meeting of the Parties, with technical support provided by a Working Group, assisted by the Ozone Secretariat based at UN Environment headquarters in Nairobi, Kenya.

As a result of actions taken under the Montreal Protocol, ozone levels have stabilized, the “Antarctic ozone hole” is gradually diminishing and overall ozone levels are forecast to reach pre-1980 levels before 2075. 3

The Montreal Protocol was the first international treaty to be ratified by all 197 members of the United Nations, while its approach to burden sharing, financial supports and multi-phase implementation set the standard for subsequent agreements, like the United Nations Framework Convention on Climate Change (UNFCCC) (1992), the Kyoto Protocol (1997), and the Paris Climate Agreement (2015). Unfortunately, the response of governments and public opinion to the more compelling issue of climate change has been considerably less effective.

For details of UN involvement in global warming, see: UN Climate Talks and Timeline.

Diagram of ozone layer in atmosphere. Montreal Protocol.
Image showing the location of good protective ozone and bad heat-trapping ozone in the troposphere. The so-called ‘bad’ ozone’s main ingredient is urban smog which is an air pollutant that is harmful to breathe. Then, there is ‘good’ ozone in the stratosphere which extends upward from about 6 to 30 miles. This good ozone protects life on Earth from the sun’s harmful ultraviolet UV rays. Image: © New Hampshire Department of Environmental Services

The Montreal Protocol is considered a success story, one in which decisions were made in an unusually timely fashion and the phase-out quite successful, notwithstanding the little bit of cheating by China. The ozone problem had a lot of momentum behind it, because the solution was simple – get rid of CFCs in spray cans and replace with pumps and roll-ons instead. We don’t have such an easy solution to climate change. A consumer can’t just switch to riding a bike instead of using their car. Unfortunately the solution to global warming doesn’t just involve people caring for the environment, it requires a gigantic international effort by industries, engineers, scientists and politicians to come up with better technology.

What Was The Background To The Montreal Protocol?

Ozone is a naturally occurring gas, produced by the action of sunlight on oxygen, which resides high up in the stratosphere at an altitude of between 12 and 19 miles above the surface of the Earth. This so-called “ozone layer” is very important because it shields us and the planet’s biosphere from ultraviolet (UV) solar radiation. Although oxygen helps to absorb the Sun’s ultraviolet radiation, only ozone absorbs the most energetic UV light, known as UV-B. The protective role of the ozone layer is so vital that life on land probably would not have evolved – without it. 4

Ozone Levels: Statistics
Total global ozone changes since the 1960s. Notice the sudden decline in the ozone layer from the beginning of the 1980s, and the start of a recovery in early 1990

During the 1950s, new aerosol products were manufactured, which used a chlorofluorocarbon (CFC) propellant called Freon-11. Similar products followed, all containing CFCs, whose nontoxic, non-flammable properties made them ideally suited for use in a very wide range of industries.

Then, in 1970, a Dutch atmospheric chemist named Paul Crutzen discovered that when nitrous oxide gets into the stratosphere, it reacts with solar energy eventually neutralizing any ozone molecules with which it comes into contact.

Crutzen’s work was not widely accepted at the time, but it helped pave the way for the efforts of Frank Sherwood Rowland and Mario Molina, two American chemists who, in 1973, began studying the impacts of CFCs on the Earth’s atmosphere.

The pair came up with the theory – to become known as the Rowland-Molina Hypothesis – that CFC molecules (like Crutzen’s nitrous oxide) would also react with sunlight and would also cause damage to ozone molecules.

Following the publication of their seminal paper in June 1974, Rowland and Molina testified before Congress in December 1974. As a result, substantial funding was made available to study various aspects of the problem and to confirm the initial findings. In 1976, despite vocal opposition from industry, the U.S. National Academy of Sciences confirmed the accuracy of the Rowland-Molina Hypothesis. 5

By 1980, scientists began to observe large decreases in atmospheric ozone levels. Satellite measurements confirmed that ozone concentrations were declining by roughly 5 percent a year. A corresponding increase of ground level UV radiation was also recorded.

Then, in 1985, the urgency of the situation became apparent. British Antarctic Survey scientists published results of extremely low ozone concentrations above Halley Bay near the South Pole. Their discovery of a so-called “ozone hole” above Antarctica shocked both scientists and public alike. (Note: the “hole” isn’t an actual hole as such but rather a large area in the ozone layer marked by a very low concentration of ozone molecules.)

“One of the most amazing things about the discovery of the ozone hole was the way it propelled environmental issues onto the centre stage of politics,” says Prof Jane Francis, director of the British Antarctic Survey. 6

Furthermore, by alerting the public as well as policy makers, to the possible damage caused to the atmosphere by certain gases, it made it easier for people to understand the impact of carbon dioxide and methane on the greenhouse effect and why international action is the only way forward.

What Was The Global Response To The Ozone Hole?

Twenty countries, including most of the major producers of CFCs, immediately signed up to The Vienna Convention for the Protection of the Ozone Layer (1985), which set up a framework to regulate ozone-depleting substances (ODSs). The Vienna Convention did not compel countries to take action to control these substances, this was left to be decided. But after satellite confirmation by the Stratospheric Aerosol and Gas Experiment (SAGE II) as to the size of the “ozone hole”, it took a mere 18 months to reach a binding agreement at Montreal.

What Did The Montreal Protocol Say?

The main purpose of the Montreal Protocol was to restrict and ultimately eliminate the use of CFCs and other ozone-depleting substances. (Note: all the ODSs regulated by the Montreal Protocol contain either chlorine or bromine.) This was not easy. Not only was the propellant industry still vociferously denying the environmental risks involved in CFCs, but poorer countries lacked the resources to develop alternative propellants.

In response, the treaty introduced two basic timetables: one for developed countries and one for developing countries (known as “Article 5 countries”). The latter were allowed to delay implementation of control provisions (Article 5) and qualified for financial assistance from the agreement’s “Multilateral Fund”.

However, all parties have specific responsibilities concerning control measures (Article 2), licensing systems for ODS imports and exports (Article 4), annual progress reports (Article 7), non-compliance (Article 8) and more. The substances regulated by the treaty are listed in Annex A (CFCs, halons), Annex B (other fully halogenated CFCs), Annex C (HCFCs), Annex E (methyl bromide) and Annex F (HFCs). 7

Timetable For Eliminating ODSs

In developed countries the manufacture and consumption of halons ceased in 1994. Certain other chemicals (e.g. CFCs, HBFCs, carbon tetrachloride, and methyl chloroform) were phased out in 1996, while methyl bromide and bromochloromethane was phased out in 2005. HCFCs are due to be eliminated by 2030.

In contrast, in developing countries CFCs, carbon tetrachloride, methyl chloroform, and halons were phased out in 2010; methyl bromide and bromochloromethane in 2015, and HCFCs are to be eliminated by 2040.

Amendments To Montreal Protocol

Since the Montreal treaty came into operation in 1987, various revisions and amendments have been made in the light of scientific and economic circumstances. Most have been introduced to accelerate and tighten up the phasing out of ODSs.

Problems With Replacements For CFCs

The group of chemicals known as “hydrofluorocarbons” (HFCs), were specially developed by industry as environmentally-friendly substitutes for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). These new HFCs are now widely used in air conditioners, refrigerators, aerosols, foams, fire extinguishers and other products.

HFCs are designed to be ozone-friendly. But according to a 2015 NASA study, HFCs also contribute to ozone depletion by a small but measurable amount. 8

What’s more, many HFCs have high global warming potentials ranging from 12 to 12,000. For example, HFC-23 is 12,400 times more powerful than CO2, which makes HFCs by far the worst greenhouse gases on the planet. Indeed, greenhouse gas emissions from HFCs are rising by 8 percent per year and annual emissions are forecast to reach between 7 and 19 percent of global CO2 emissions by 2050. 7

The issue of HFCs was addressed by the Kigali Amendment to the Montreal Protocol in 2016.

Kigali Amendment To The Montreal Protocol

After seven years of negotiations, the signatories to the Montreal Protocol agreed at Kigali, Rwanda, to add hydrofluorocarbons (HFCs) to the list of controlled ozone-depleting substances, and pledged to reduce the use of HFCs by more than 80 percent by the 2040s. By the end of 2018, some 65 countries had ratified the Amendment. 9

The first reductions imposed by developed countries are expected in 2019. Most developing countries will freeze consumption in 2024, with a small number of developing countries following in 2028. The plan also provides extra financial support for certain countries, to help them switch to alternatives that do not interfere with Earth’s climate system or impact on global warming.

The Kigali regulation of HFCs is estimated to result in a saving of 80 billion metric tons worth of CO2-equivalent emissions by 2050, helping to reduce global temperature projections by up to 0.5°C by the end of the century, while still protecting the ozone layer. 10

Advisory Bodies

The Parties to the Montreal Protocol have several advisory bodies called Assessment Panels. These panels are responsible for publishing regular reports on the phaseout of ozone-depleting substances, and many other matters.

• In 1990, for example, a Technology and Economic Assessment Panel (TEAP) was established to support ongoing work under the treaty. 11 TEAP provides technical data concerning the alternative technologies on offer to eliminate the use of substances that harm the ozone layer. TEAP also advises the Parties through its annual reports on technical issues such as essential use exemptions for CFCs and halons.

• Other advisory boards include: the Scientific Assessment Panel (SAP) which monitors and assesses data on the depletion of the ozone layer, and associated issues of atmospheric science; the Environmental Effects Assessment Panel (EEAP) which analyzes the current effects of ozone layer depletion. 7

What Is The Montreal Protocol’s Multilateral Fund?

• The Multilateral Fund for the Implementation of the Montreal Protocol was set up in 1991, under Article 10 of the treaty, in order to help “Article 5 countries” to comply with the control measures of the Protocol. Currently, 147 of the 196 signatories to the Montreal Protocol qualify as Article 5 countries.

• The Multilateral Fund is run by an Executive Committee divided between seven industrialized and seven developing countries, which is elected annually at the Meeting of the Parties. The Committee reports annually to the Meeting of the Parties on its plans and work.

• Fund payments are used to finance compliance with the regulatory measures of the treaty. Funded projects include those concerned with the conversion of existing manufacturing processes, the training of personnel, the organization of patent rights for new technologies, and the setting up of national ozone offices.

• The Fund is administered by a Multilateral Fund Secretariat, based in Montreal. In developing countries, the work of the Multilateral Fund is carried out by four international agencies – the UN Environment (UNEP), the UN Development Programme (UNDP), the UN Industrial Development Organisation (UNIDO) and the World Bank – as well as bilateral agencies of non-Article 5 countries, all of whom report to the Executive Committee. 12

• Since its launch the Multilateral Fund has supported well over 8,600 projects worth over US$3.9 billion. It has served as an important precedent for later support mechanisms included in the UNFCCC (1992). For more, see: the Ethics of Climate Change.

Has The Montreal Protocol Solved The Ozone Problem?

Well things are definitely improving, no question. At the end of 2018, the United Nations issued a scientific assessment stating that the ozone layer was improving and predicting that it would recover completely in the Northern Hemisphere (excluding the polar region) by the 2030s, followed by the Southern Hemisphere in the 2050s and polar regions by 2060. According to NASA researchers, ozone depletion over Antarctica has improved by 20 percent since 2005. 13

Furthermore, since the Montreal Protocol came into effect, 99 percent of nearly 100 ozone-depleting chemicals have been or are being phased out. In addition, atmospheric levels of the key chlorofluorocarbons (CFCs) and related chlorinated hydrocarbons have either stabilized or decreased. 14

Anomalies persist, however. In 2018, scientists monitoring atmospheric chemistry reported evidence of continuing industrial production of CFC-11, most likely in eastern Asia, with obvious adverse effects on the ozone layer. 15 16

Meantime another study found signs of new releases of carbon tetrachloride emanating from Shandong province in the eastern part of China, on the lower reaches of the Yellow River. The illicit emissions began way back in 2012, and account for a significant percentage of excess emissions under the Montreal Protocol. 17

What Are The Health Benefits Of The Montreal Protocol?

According to forecasts by the U. S. Environmental Protection Agency in 2015, the renewal of the ozone layer under the treaty will prevent more than 280 million cases of skin cancer, 1.5 million skin cancer deaths, and 45 million cataracts in the United States. 18

According to Rolando Garcia, a senior scientist at the U.S. National Center for Atmospheric Research (NCAR) and a co-author of two studies on the environment, global climate would be at least 25 percent hotter today without the Protocol. 19

Has The Montreal Protocol Helped To Reduce Global Warming?

Yes and No.

Yes, because at least one study has shown that the contribution of ozone-depleting substances (ODS) to global warming most likely, would have been far greater if the ODS link to stratospheric ozone depletion had not been recognized in 1974, and followed by a series of regulations laid down by the Montreal Protocol. 20 What’s more, the Montreal pact set a wonderful example for international cooperation in pursuit of an important environmental goal, and alerted the world to the dangers of environmental negligence.  

No, because the HCFCs and HFCs initially approved by the Montreal Protocol as safer alternatives to CFCs, are now recognized as being some of the worst greenhouse gases on the planet.


  1. “Deal reached on HFC greenhouse gases.” McGrath, Matt. BBC News. 15 October 2016. []
  2. “Adjustments to the Montreal Protocol”. United Nations Environment Programme Ozone Secretariat. []
  3. The Antarctic Ozone Hole Will Recover”. NASA. June 4, 2015. []
  4. “Ozone in the Stratosphere.” Jennifer Bergman. Windows to the Universe. 2007. []
  5. National Academy of Sciences (1976). “Halocarbons, effects on stratospheric ozone.” Washington, DC. []
  6. “Ozone layer hole: How its discovery changed our lives.” BBC News. 16 May, 2015. []
  7. About Substances that Deplete the Ozone Layer”. UN Environment. [][][]
  8. Ozone depletion by hydrofluorocarbons.” Margaret M. Hurwitz, et al. Geophysical Research Letters. Volume 42, Issue 20. Pages 8686-8692. October 2015. []
  9. “Kigali Amendment heralds new dawn for climate change action.” Joyce Msuya. The Standard. January 2, 2019. []
  10. “Recent International Developments under the Montreal Protocol.” U.S. Environmental Protection Agency. []
  11. “Technology and Economic Assessment Panel, Ozone Secretariat”. []
  12. “Creating a real change for the environment.” Secretariat of the Multilateral Fund for the Implementation of the Montreal Protocol. 2007. []
  13. Ozone depletion, explained.” Christina Nunez. National Geographic. April 18, 2019. []
  14. “Has the Montreal Protocol been successful in reducing ozone-depleting gases in the atmosphere?” U.S. NOAA (PDF) []
  15. “Banned Ozone-Depleting Chemical Is Still Being Produced Somewhere, Scientists Say.” National Public Radio (NPR). May 17, 2018. []
  16. An unexpected and persistent increase in global emissions of ozone-depleting CFC-11.” Stephen A. Montzka; et al. Nature. 557 (7705): 413–417. []
  17. Continued Emissions of the Ozone-Depleting Substance Carbon Tetrachloride from Eastern Asia.” M. F. Lunt; et al. Geophysical Research Letters. 45 (20): 11, 423–11, 430. September 28, 2018. []
  18. “Updating Ozone Calculations and Emissions Profiles for Use in the Atmospheric and Health Effects Framework Model.” U. S. Environmental Protection Agency. 2015. []
  19. “Without the Ozone Treaty You’d Get Sunburned in 5 Minutes.” Stephen Leahy. National Geographic. Sept 25, 2017. []
  20. The importance of the Montreal Protocol in protecting climate.” Guus J. M. Velders, Stephen O. Andersen, John S. Daniel, David W. Fahey, Mack McFarland. Proceedings of the National Academy of Sciences 104(12):4814-9. April 2007. []
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