The Montreal Protocol, officially called the Montreal Protocol on Substances That Deplete the Ozone Layer, is an international treaty created to protect the ozone layer by stopping the use of many substances that harm it. It was signed on September 16, 1987, and became active on January 1, 1989. Over time, the treaty has been updated several times, with changes agreed to in 1990 (London), 1992 (Copenhagen), 1995 (Vienna), 1997 (Montreal), 1999 (Beijing), 2007 (Montreal), 2016 (Kigali), and 2018 (Quito).

The Montreal Protocol has been officially approved by 198 countries and the European Union, making it the first treaty in United Nations history to be fully accepted by all nations. Because of its widespread use and success, it is considered a strong example of countries working together. Former United Nations Secretary-General Kofi Annan said, "perhaps the single most successful international agreement to date has been the Montreal Protocol."

Because of the treaty, the large hole in Earth's ozone layer above Antarctica is slowly getting smaller. Scientists predict that the ozone layer will return to its 1980 condition by 2040 in most parts of the world and by 2066 over Antarctica.

Terms and purposes

The Montreal Protocol sets rules for controlling harmful chemicals called ozone-depleting substances (ODS). These rules include when to stop using these chemicals, how to check progress, how to report data, how to handle countries that do not follow the rules, and how to help developing countries follow the rules.

The timeline for stopping the use of ODS is divided into groups based on the type of chemical. Each group has specific chemicals listed in the Protocol’s annexes.

Article 5 of the Protocol gives developing countries extra time to follow the rules. Article 10 sets up a system to provide financial help to these countries.

The goal of the Protocol is for all signatory countries to:

The substances in Group I of Annex A include:
• CFCl₃ (CFC-11)
• CF₂Cl₂ (CFC-12)
• C₂F₃Cl₃ (CFC-113)
• C₂F₄Cl₂ (CFC-114)
• C₂F₅Cl (CFC-115)

For non-Article 5 countries, production and use of these chemicals stopped on July 1, 1989, at the 1986 level. By 1994, use was reduced by 75%, and by 1996, all use was stopped. For Article 5 countries, use stopped at the average level from 1995–1997. By 2005, use was reduced by 50%, by 2007 by 85%, and by 2010, all use was stopped. Some chemicals, like carbon tetrachloride and 1,1,1-trichloroethane, had special rules. The use of less harmful HCFCs began to stop in 1996 and will fully stop by 2030.

For Group II of Annex A (halons: halon-1211, -2404, and -1301), non-Article 5 countries stopped production and use on January 1, 1992, at the 1986 level, with full stop by 1994. For Article 5 countries, use stopped on January 1, 2002, at the average level from 1995–1997. By 2005, use was reduced by 50%, and by 2010, all use was stopped.

Some uses of ODS are allowed if no substitutes are available, such as metered dose inhalers for asthma and fire suppression systems in submarines and aircraft.

The Protocol requires countries to make decisions based on scientific, environmental, technical, and economic information reviewed by experts. Reports on these topics were published in 1989, 1991, 1994, 1998, and 2002 by the Scientific Assessment Panel (SAP).

In 1990, the Technology and Economic Assessment Panel (TEAP) was created to advise on alternatives to ODS. TEAP evaluates technical issues, such as exemptions for essential uses, and provides reports to help countries make informed decisions.

Many organizations have studied and shared information about alternatives to ODS, which are used in areas like refrigeration, air conditioning, foam, fire protection, and agriculture.

Under the Montreal Protocol, developed countries began reducing HCFC use in 2004 and fully stopped by 2020. Developing countries agreed to freeze HCFC use in 2013, start reducing it in 2015, and fully stop by 2030.

Hydrochlorofluorocarbons (HCFCs) are man-made chemicals containing hydrogen, chlorine, fluorine, and carbon. They were used after CFCs were phased out because they cause less harm to the ozone layer. HCFCs are used in refrigeration, aerosols, foam, and air conditioning. While they break down more quickly in the atmosphere than CFCs, they are still strong greenhouse gases.

HCFCs have lower ozone depletion potential (ODP) than CFCs (0.01–0.5 vs. 0.6–1.0) and lower global warming potential (GWP) (76–2,270 vs. 4,680–10,720).

The Kigali Amendment to the Montreal Protocol, which started on January 1, 2019, requires countries to reduce the use of hydrofluorocarbons (HFCs) by more than 80% over 30 years. By December 2018, 65 countries had approved the amendment. As of October 2024, 160 countries and the European Union had approved it.

HFCs replaced CFCs and HCFCs because they do not harm the ozone layer (they lack chlorine). However, they are strong greenhouse gases. A study suggested reducing HFCs could prevent up to 8.8 billion tons of CO₂-equivalent emissions by 2050 and avoid up to 0.5°C of warming by 2100. The Kigali Amendment was approved in 2016 after years of talks.

Developing countries, including China, Brazil, and South Africa, must reduce HFC use by 85% of their average from 2020–2022 by 2045. India and other countries, like Iran and Saudi Arabia, must reduce HFC use by 85% of their average from 2024–2026 by 2047.

On November 17, 2017, Sweden became the 20th country to approve the Kigali Amendment, meeting the number needed for it to take effect.

History

In 1974, chemists Frank Sherwood Rowland and Mario Molina at the University of California, Irvine began studying how CFCs affected Earth's atmosphere. They found that CFC molecules remained in the atmosphere until they reached the middle of the stratosphere, where ultraviolet radiation broke them down, releasing chlorine atoms. Rowland and Molina then suggested that these chlorine atoms might cause large amounts of ozone (O₃) in the stratosphere to break down. In 1976, the U.S. National Academy of Sciences released a report that supported the idea that CFCs could reduce ozone levels.

In 1982, representatives from 24 countries met in Stockholm, Sweden, to create a "Global Framework Convention for the Protection of the Ozone Layer." The following year, a group of countries, including the United States, Canada, the Nordic Countries, and Switzerland, proposed a worldwide ban on "nonessential" uses of CFCs in spray cans.

In 1985, scientists Joe Farman, Brian Gardiner, and Jon Shanklin from the British Antarctic Survey reported unusually low ozone levels above Halley Bay near the South Pole. They believed this was linked to rising CFC levels in the atmosphere. This discovery, along with NASA images of the ozone hole, helped shape the Montreal Protocol negotiations. The term "ozone hole" and visual animations showing the hole's size convinced negotiators in Montreal, Canada, to address the issue seriously.

Also in 1985, 20 nations, including most major CFC producers, signed the Vienna Convention. This agreement created a plan for international rules about substances that harm the ozone layer. From the discovery of the ozone hole, it took only 18 months to reach a binding agreement in Montreal, Canada. Mostafa Kamal Tolba, then head of the UNEP, was called the "father of the Montreal Protocol" for helping nations agree on the plan.

In 1986, a study led by NASA and supported by the United Nations Environment Program, the World Meteorological Organization, and other groups concluded that if CFC emissions continued at 1980 levels, global ozone levels would drop by about 9% by the late 2000s. Based on these findings, the U.S. Environmental Protection Agency estimated that in the United States alone, over 150 million new cases of skin cancer could occur among people alive today and born by 2075, leading to over 3 million deaths.

The CFC industry resisted regulation as late as 1986. The Alliance for Responsible CFC Policy, an organization representing CFC producers including DuPont, argued that the science was too uncertain to justify action. In 1987, DuPont told the U.S. Congress that "there is no imminent crisis that demands unilateral regulation." Even in March 1988, DuPont's chairman, Richard E. Heckert, wrote to the U.S. Senate that "scientific evidence does not point to the need for dramatic CFC emission reductions."

However, in 1986, the Alliance for Responsible CFC Policy stated that large increases in CFCs would be harmful to future generations and that ignoring risks to them would conflict with the industry's goals. Three months before the Montreal Protocol negotiations began, U.S. industry announced support for new international rules to control CFC use.

Multilateral Fund

The main goal of the Multilateral Fund for the Montreal Protocol is to help developing countries that use less than 0.3 kg of ozone-depleting substances (ODS) per person each year follow the rules of the Protocol. These countries are called Article 5 countries, and 147 out of the 196 countries that signed the Montreal Protocol meet this requirement.

This fund reflects a principle agreed to in 1992 at the United Nations Conference on Environment and Development, which states that all countries share responsibility for protecting the environment, but developed and developing countries have different roles based on their abilities.

The fund is managed by an executive committee with seven members from developed countries and seven from Article 5 countries. These members are chosen each year by a meeting of all Protocol signatories. The committee reports its work to this meeting every year. In developing countries, the fund’s activities are carried out by four agencies that have agreements with the committee:

• United Nations Environment Programme (UNEP), through its OzonAction Programme.
• United Nations Development Programme (UNDP).
• United Nations Industrial Development Organization (UNIDO).
• World Bank.

Up to 20% of the money given by countries can also be sent through their own agencies to support approved projects and activities in developing nations.

The fund is refilled every three years by donors. From 1991 to 2005, donors pledged a total of $3.1 billion. This money is used for tasks such as helping factories switch to safer methods, training workers, paying fees for using new technology, and creating national offices to manage ozone-related work.

Parties

As of October 2022, all countries that are part of the United Nations, along with the Cook Islands, Niue, the Holy See, the State of Palestine, and the European Union, have agreed to the original Montreal Protocol. The State of Palestine was the last to agree to this agreement, making the total number of participants 198. Out of these 198, 197 (excluding the State of Palestine) have also agreed to the London, Copenhagen, Montreal, and Beijing amendments to the protocol.

Effect

Since the Montreal Protocol began, the amounts of important chlorofluorocarbons (CFCs) and related chlorinated hydrocarbons in the atmosphere have either stayed the same or decreased. Halon levels have continued to rise because halons stored in fire extinguishers are being released, but the rate of increase has slowed. Scientists expect halon levels to begin decreasing by about 2020. Hydrochlorofluorocarbons (HCFCs) increased greatly because they were used as replacements for CFCs in products like refrigerants and solvents. Although some people have tried to break the ban by smuggling CFCs from undeveloped to developed countries, most nations have followed the rules. A 2010 study showed that the Montreal Protocol has helped protect the ozone layer in the upper atmosphere. Because of this, the Protocol is often called the most successful international environmental agreement. In 2001, NASA found that the thinning of the ozone layer over Antarctica had not changed for three years, but in 2003, the ozone hole grew to its second-largest size. A 2006 report said the Protocol is working, as evidence shows fewer ozone-depleting chemicals in the air and early signs that the ozone layer is healing. However, a more recent study suggests there may be an unknown source causing CFC levels to rise again.

A 2002 report predicted the ozone layer would return to 1980 levels by the middle of the 21st century. A 2022 report delayed this timeline to 2066 for Antarctica, 2045 for the Arctic, and 2040 for most of the world. Scientists believe this change is due to updated calculations and changes in the atmosphere.

In 1997, scientists found that Russia produced large amounts of CFCs for sale on the black market in the 1990s. In the United States, some companies used CFCs illegally because of weak enforcement. Similar illegal CFC trade was also found in Taiwan, Korea, and Hong Kong.

The Montreal Protocol is expected to improve human health. A 2015 report by the U.S. Environmental Protection Agency estimated that protecting the ozone layer would prevent over 280 million cases of skin cancer, 1.5 million skin cancer deaths, and 45 million cataracts in the United States.

However, HCFCs and HFCs contribute to human-caused global warming. These chemicals are up to 10,000 times more powerful as greenhouse gases than carbon dioxide. The Montreal Protocol requires HCFCs to be completely phased out by 2030 but does not limit HFCs. Replacing CFCs with HFCs does not greatly increase climate change risks, but using more HFCs over time could worsen global warming.

Experts suggest combining efforts to protect the ozone layer with climate change solutions because decisions in one area can affect the other.

In 2016, the Kigali Amendment to the Montreal Protocol was signed, which reduces the use of HFCs. This made the Protocol both an ozone and climate treaty because HFCs are strong greenhouse gases.

As of November 2025, the European Union is on track to meet its HFC reduction goals under the Montreal Protocol.

Compared to other environmental treaties, the Montreal Protocol succeeded because countries shared responsibilities fairly and created solutions that addressed regional concerns. This was different from the Kyoto Protocol, which failed to do so. Also, global rules to protect the ozone layer were already in place before scientists fully agreed on the problem. People worldwide were also aware of the risks to the environment.

In 2018, scientists found evidence of illegal CFC-11 production in eastern Asia, which harms the ozone layer. Another study found new releases of carbon tetrachloride from China’s Shandong province, which contributed to higher emissions than expected under the Montreal Protocol.

25th anniversary celebrations

The year 2012 celebrated the 25th anniversary of the signing of the Montreal Protocol. To honor this milestone, the Montreal Protocol community planned events at the national, regional, and international levels. These events shared information about the protocol’s achievements and discussed future goals. Key accomplishments of the Montreal Protocol include:

• It was the first international agreement to address a global environmental challenge.
• It was the first to use the "precautionary principle," which means making decisions based on scientific evidence even when some risks are not fully understood.
• It was the first treaty to allow independent experts in areas like atmospheric science, environmental effects, chemical technology, and economics to report directly to countries without changes or restrictions. These experts worked with rules that ensured fairness and accuracy.
• It was the first agreement to recognize that countries have different abilities and responsibilities. It created a fund to help countries share technology and resources.
• It was the first treaty with strict rules for all countries, including developed and developing nations, to report on activities, control trade, and stop using harmful chemicals.
• It was the first treaty to manage a financial system democratically, with equal representation from both developed and developing countries.

Within 25 years of being signed, the Montreal Protocol reached important goals. The world has stopped using 98% of the ozone-depleting substances in nearly 100 dangerous chemicals. All countries are following strict rules. The Montreal Protocol is the first global agreement that every country has joined, including South Sudan, which became a member in 2013. The United Nations Environment Programme praised the agreement for showing the world’s commitment to protecting the ozone layer and the environment overall.