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

The Montreal Protocol has been approved by 198 countries and the European Union, making it the first treaty in United Nations history to be signed by all nations. Because of its widespread use and success, it is seen as a great 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 Protocol, the large hole in the ozone layer above Antarctica is slowly getting smaller. Scientists predict the ozone layer will return to its 1980 condition by 2040 in most parts of the world and by 2066 above Antarctica.

Terms and purposes

The Montreal Protocol sets rules for controlling ozone-depleting substances (ODS), including when they must be phased out, how progress is reviewed, how data is shared, how to handle countries that do not follow the rules, and how to help developing countries meet the rules.

Timelines for stopping the use of ODS are grouped by type. Specific ODS in each group are listed in the Protocol’s annexes.

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

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 substances stopped at 1986 levels on July 1, 1989. By 1994, 75% of these substances were reduced, and by 1996, all use was stopped. For Article 5 countries, use and production stopped at average 1995–97 levels. By 2005, 50% were reduced; by 2007, 85% were reduced; and by 2010, all use was stopped. Some chemicals, like carbon tetrachloride and 1,1,1-trichloroethane, had special rules. HCFCs, which are less harmful than CFCs, began being phased out in 1996 and will be fully phased out by 2030.

For Group II substances in Annex A (halons like halon-1211, -2404, and -1301), non-Article 5 countries stopped production and use at 1986 levels on January 1, 1992, with full phase-out by 1994. Article 5 countries stopped production and use at average 1995–97 levels on January 1, 2002. By 2005, 50% were reduced, and by 2010, all use was stopped.

Some uses of ODS, like metered dose inhalers for asthma and fire suppression systems in submarines and aircraft, were allowed to continue for a time because no safe substitutes were found.

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

In 1990, the Technology and Economic Assessment Panel (TEAP) was created to advise on alternatives to ODS and evaluate technical issues. TEAP also reviews requests for exemptions for essential uses of CFCs and halons and for critical uses of methyl bromide.

Many organizations have studied alternatives to ODS used in refrigeration, air conditioning, foam, fire protection, aerospace, electronics, agriculture, and labs.

Under the Montreal Protocol, developed countries began reducing HCFC use in 2004 and production in 2010, aiming for full reduction by 2020. Developing countries agreed to start reducing HCFC use and production by 2015, aiming for full reduction by 2030.

HCFCs are man-made chemicals containing hydrogen, chlorine, fluorine, and carbon. They were used after CFCs were phased out in the 1980s because CFCs damaged the ozone layer. HCFCs are used in refrigeration, aerosols, foam, and air conditioning. Unlike CFCs, HCFCs break down in the lower atmosphere and cause less ozone damage. However, HCFCs are strong greenhouse gases, even though they are present in very small amounts.

HCFCs are temporary replacements for CFCs. They are used as refrigerants, solvents, blowing agents for foam, and fire extinguishers. Compared to CFCs, HCFCs have lower ozone depletion potential (ODP) and lower global warming potential (GWP).

The Kigali Amendment to the Montreal Protocol, which started on January 1, 2019, requires countries to reduce hydrofluorocarbon (HFC) use 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, which are mostly made in developed countries, replaced CFCs and HCFCs. Unlike CFCs and HCFCs, HFCs do not contain chlorine and do not harm the ozone layer. 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.

In 2016, the Kigali Amendment was approved at the 28th Meeting of the Parties in Kigali. The amendment requires signatory countries to reduce HFC production and use by at least 85% from 2011–2013 levels. Developing countries like China, Brazil, and South Africa must reduce HFC use by 85% of their 2020–2022 average by 2045. India and other countries, including Iran, Iraq, Pakistan, Saudi Arabia, and Kuwait, must reduce HFC use by 85% of their 2024–2026 average by 2047.

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

History

In 1974, chemists Frank Sherwood Rowland and Mario Molina at the University of California, Irvine studied the effects of CFCs in Earth's atmosphere. They found that CFC molecules remained in the atmosphere for a long time until they reached the middle of the stratosphere, where ultraviolet radiation broke them apart, releasing chlorine atoms. Rowland and Molina 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 harm the ozone layer.

In 1982, representatives from 24 countries met in Stockholm, Sweden, to create a "Global Framework Convention for the Protection of the Ozone Layer." The next 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 showing an ozone hole, helped shape the Montreal Protocol negotiations. The term "ozone hole" and visual animations of the hole's size convinced negotiators in Montreal, Canada, to address the issue seriously.

Also in 1985, 20 nations, including major CFC producers, signed the Vienna Convention. This agreement set rules for international regulations on 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 uniting nations to create the agreement.

In 1986, a study led by NASA and supported by the United Nations Environment Program, the World Meteorological Organization, and other groups warned that continuing CFC emissions at 1980 levels would reduce global average ozone by about 9 percent by the late 20th century. Based on this, the U.S. Environmental Protection Agency estimated that over 150 million new skin cancer cases could occur in the United States by 2075, leading to over 3 million deaths.

The CFC industry resisted regulation until 1986, when the Alliance for Responsible CFC Policy (founded by 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." In March 1988, DuPont's chair, 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 future increases in CFCs would be unacceptable to future generations" and that ignoring risks to future generations would conflict with industry goals. Three months before the Montreal Protocol negotiations began, U.S. industry announced support for new international controls on CFCs.

Multilateral Fund

The main goal of the Multilateral Fund for the Montreal Protocol is to help developing countries that meet specific conditions. These countries must have an average yearly use and production of ozone-depleting substances (ODS) less than 0.3 kg per person. These countries are called Article 5 countries. Out of the 196 countries that are part of the Montreal Protocol, 147 meet these conditions.

This fund follows a principle agreed to in 1992 at the United Nations Conference on Environment and Development. The principle states that all countries share a responsibility to protect the environment, but the level of responsibility depends on each country’s situation.

The fund is managed by an executive committee. This committee has equal numbers of seven industrialized countries and seven Article 5 countries. These members are chosen each year by a group of countries that meet to discuss the Protocol. The committee reports its work to this group every year. In developing countries, the fund’s work is 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 money given to the fund by countries can be sent through their own agencies to support projects that meet the fund’s goals.

The fund is refilled every three years by donors. From 1991 to 2005, donors pledged $3.1 billion. This money is used for tasks such as changing old manufacturing methods, training workers, paying for technology rights, and creating national offices to manage ozone-related issues.

Parties

As of October 2022, all United Nations member countries, 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 join, making the total number of signatories 198. Out of these 198, 197 have also agreed to the London, Copenhagen, Montreal, and Beijing amendments.

Effect

Since the Montreal Protocol was introduced, the amounts of the most 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 amounts to begin decreasing by about 2020. Hydrochlorofluorocarbons (HCFCs) have increased greatly, partly because they were used as substitutes for CFCs in applications like refrigeration and cleaning. While some people have tried to break the ban by smuggling CFCs from less developed to more developed countries, overall, most nations have followed the rules. A 2010 study showed that the Montreal Protocol has helped protect the ozone layer in the stratosphere. Because of this, the Montreal Protocol is often called the most successful international environmental agreement. In 2001, NASA reported that the thinning of the ozone layer over Antarctica had not changed for three years, but in 2003, the ozone hole reached its second-largest size. A 2006 report stated, "The Montreal Protocol is working: There is clear evidence that the amounts of ozone-depleting substances in the atmosphere are decreasing, and early signs of ozone recovery are appearing." However, a more recent study suggests that CFC levels may have increased slightly due to an unknown source.

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

In 1997, it was reported that Russia produced significant amounts of CFCs for sale on the black market to the European Union during the 1990s. In the United States, illegal use of CFCs was linked to false reports, which were made possible by weak enforcement. Similar illegal CFC markets were found in Taiwan, Korea, and Hong Kong.

The Montreal Protocol is also expected to affect human health. A 2015 report by the U.S. Environmental Protection Agency estimated that protecting the ozone layer under the Protocol will 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 hydrofluorocarbons (HFCs) contribute to human-caused global warming. These compounds are up to 10,000 times more powerful as greenhouse gases than carbon dioxide. The Montreal Protocol requires the complete phase-out of HCFCs by 2030 but does not restrict HFCs. While replacing CFCs with HFCs does not significantly increase climate change risks, continued use of HFCs could increase the risk over time.

Experts suggest that efforts to protect the ozone layer and reduce climate change should be connected. Decisions in one area can affect the costs and success of environmental improvements in the other.

In 2016, the Kigali Amendment was added to the Montreal Protocol. This amendment reduces the production and use of HFCs, which are strong greenhouse gases. Because of this, the Montreal Protocol now addresses both ozone protection and climate change.

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

Compared to other environmental agreements, the success of the Montreal Protocol is linked to fair sharing of responsibilities and solutions that reduce conflicts between regions. Unlike the Kyoto Protocol, which failed to address these issues, the Montreal Protocol had global rules in place before scientific agreement was reached. Public support for the agreement was also strong because people understood the risks of ozone depletion.

In 2018, scientists found evidence of ongoing industrial production of CFC-11, likely in eastern Asia, which harms the ozone layer. A study also detected new releases of carbon tetrachloride from China's Shandong province, beginning after 2012, which contributed to emissions exceeding global estimates under the Montreal Protocol.

25th anniversary celebrations

In 2012, the world celebrated the 25th anniversary of the Montreal Protocol. This agreement, signed by many countries, was created to protect the ozone layer. To mark this milestone, groups connected to the Montreal Protocol planned events at local, national, and global levels. These events shared the progress made so far and discussed future goals. Some important achievements of the Montreal Protocol include:

• It was the first international agreement to solve a major global environmental problem.
• It was the first to use the "precautionary principle," which means making decisions based on scientific evidence even when some information is uncertain.
• It was the first treaty where scientists and experts from different fields, such as atmospheric science, environmental impacts, chemical technology, and economics, gave direct reports to the countries involved. These reports were shared without changes or censorship, following rules of professionalism and peer review.
• It was the first agreement to recognize that countries have different abilities and responsibilities. It created a fund to help countries share technology and support each other.
• It was the first Multilateral Environmental Agreement (MEA) to require all countries, both developed and developing, to follow strict rules about reporting, trade, and stopping the use of harmful chemicals.
• It was the first treaty to have a financial system managed by an executive board with equal representation from 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 found in nearly 100 harmful chemicals. Every country follows the strict rules set by the agreement. The Montreal Protocol is now the first global agreement that all countries have officially agreed to follow. Even the newest country to join, South Sudan, agreed to the treaty in 2013. The United Nations Environment Programme (UNEP) was praised for helping countries reach an agreement that shows the world's commitment to protecting the ozone layer and the environment overall.