The history of the Montreal Protocol, the only universally ratified treaty in UN history

View when each UN member signed the Montreal Protocol

Adopted in 1987 to phase out ozone-depleting substances, the agreement achieved universal ratification by all 197 UN member states, making it the first and only such international treaty in the UN's history.

The Montreal Protocol helped prevent significant quantities of greenhouse gas emissions

By phasing out ozone-depleting chemicals between 1990 and 2010, the Montreal Protocol prevented emissions equal to 135 gigatons of CO₂—avoiding an estimated 0.5 to 1 degrees Celsius of additional global warming by 2100.

How the Montreal Protocol supported developing nations in phasing out ozone-depleting substances

Established in 1991, the Multilateral Fund for the Montreal Protocol finances developing nations' transition to cleaner technologies. It has disbursed more than $4B across more than 140 countries and was the first financial mechanism created under an international treaty.

How amendments to the Montreal Protocol have expanded global ozone protections

Since 1990, five major amendments—London, Copenhagen, Montreal, Beijing, and Kigali—have accelerated chemical phase-outs, added new substances, such as hydrochlorofluorocarbons, and tightened enforcement.

Go inside the global effort that led to the Montreal Protocol in this narrative podcast

Nobel laureate Mario Molina and other key voices recount how science and diplomacy converged to develop a plan to close the ozone hole, offering insight into history's most successful environmental treaty.

Why a Montreal Protocol amendment cut back on the replacements for CFCs

Hydrofluorocarbons were introduced in the 1990s as ozone-safe substitutes for chlorofluorocarbons and hydrochlorofluorocarbons. However, scientists later found that they trap thousands of times more thermal energy in the atmosphere than carbon dioxide does, prompting a 2016 amendment to the Protocol to phase them out.

How scientists earned themselves a Nobel Prize by discovering what destroyed ozone

In 1974, chemists Mario Molina and F. Sherwood Rowland showed that chlorofluorocarbons—then used as aerosol propellants, refrigerants, and industrial solvents—rise into the stratosphere and, upon being struck by ultraviolet radiation, release chlorine atoms, which break apart ozone molecules. Their work earned them the Nobel Prize in chemistry in 1995.

How a black market for banned refrigerants still threatens ozone recovery and climate progress

Despite the Montreal Protocol's success, illegal trade in chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons persists. Driven by high profits and weak enforcement, smugglers supply banned refrigerants, causing significant ozone depletion and greenhouse gas emissions equivalent to billions of tons of carbon dioxide.

Learn why the Montreal Protocol may help prevent millions of cancer deaths

By restoring the ozone layer and reducing ultraviolet exposure, full implementation of the Montreal Protocol is expected to prevent about 443 million cases of skin cancer, 2.3 million skin cancer deaths, and 63 million cases of cataracts among Americans born from 1890 to 2100.

The ozone layer is on track to recover to pre-1980 levels by mid-century

Thanks to the Montreal Protocol, the ozone layer is steadily recovering and, according to a 2022 assessment, is expected to return to 1980 levels by 2040 globally, 2045 over the Arctic, and 2066 over Antarctica.

Watch a 1986 television special about the discovery of the ozone hole

The groundbreaking discovery of the Antarctic ozone hole in the mid-1980s marked a critical turning point, galvanizing international action to address the ozone-depleting properties of chlorofluorocarbons, which had been identified about a decade earlier. This environmental crisis was brought vividly to public attention through media pieces like this one.

How a skin cancerous growth shifted an initially skeptical President Reagan on the ozone crisis

While a 1985 Nature study revealing the Antarctic ozone hole jolted public concern, Reagan's administration was more focused on the Cold War than on environmental policy. His health scare and the market potential for developing alternatives to chlorofluorocarbons helped turn the tide, leading to the Montreal Protocol's unanimous ratification by a bipartisan Senate in 1988.

How sunlight helps chlorofluorocarbons destroy the ozone molecules that block solar radiation

CFCs, which are used in old refrigerants, air conditioners, and aerosol sprays, do not react with atmospheric molecules. Once they reach the stratosphere, ultraviolet radiation breaks chlorine atoms off of them, which can each break apart more than 100,000 ozone molecules, thinning Earth's protective layer against ultraviolet radiation.

A UN-led treaty may establish rules to phase out plastic globally

With support from more than 175 nations, a treaty led by the United Nations is being negotiated to establish enforceable global rules for plastic production and pollution by 2025. Negotiations come as the total amount of plastic in the ocean has increased by 50% from 2017 to 2022.

The international agreement to address antimicrobial resistance

Antimicrobial resistance has become an increasingly glaring problem for both health and agriculture. In 2024, the United Nations announced a new suite of clear actions and targets that—taken together with existing efforts—can help address superbugs in a meaningful way and on a global scale. This page from the UN lays out these efforts, with links to additional information on the many aspects of the initiative.

The international trademark framework is called the Madrid Protocol

Trademarks vary from country to country, but an agreement called the Madrid Protocol allows trademark protections across more than 100 participating countries. While the Madrid Protocol expands trademark access, it doesn't necessarily grant blanket protections across the participating countries, meaning each country is still in charge of its own trademark enforcement.

'Last Week Tonight' explores the risks of forever chemicals (warning: language)

Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals used in a wide range of products due to their unique properties. However, because they can persist in the body and environment for thousands of years, they’ve earned the moniker “forever chemicals”—and have been linked with numerous health risks.

The GATT and its successor, the WTO, were established to lower trade barriers

Signed in 1947, the General Agreement on Tariffs and Trade began systematically reducing tariffs and trade barriers among member nations. In 1995, it was replaced by the World Trade Organization, which expanded those rules and established a formal dispute settlement system.

The Clean Water Act became the national standard for protecting American waters

Enacted in 1972, the Clean Water Act grants the Environmental Protection Agency the authority to regulate pollutant discharges, establish water quality standards, and oversee water pollution controls. Its scope has narrowed due to recent Supreme Court rulings.

A look at Mauna Loa, which produces the gold standard of global CO2 measurements.

Mauna Loa Observatory is a station that measures the elements in the atmosphere that contribute to climate change. It is located on the side of the Mauna Loa volcano in Hawaii. 

The theory of chemtrails originated from misinterpreting a US Air Force paper

The document proposed a future weather modification system to achieve military objectives, but clarified that such a system "does not reflect current military policy, practice, or capability." Past testing of biological and chemical weapons has accelerated conspiracies about streaks of condensation trailing aircraft to be harmful chemical agents.

Learn about historical uses of bioremediation, the oldest cleanup method on Earth

Biochemical reactions that decompose complex molecules into simpler ones have occurred on Earth for as long as life has existed and have gradually transformed the planet into a celestial body that is increasingly habitable to greater biodiversity. Along the way, modern, human-made bioremediation techniques began to take shape in Santa Maria, California, in the 1960s.

Key milestones in the history of the World Health Organization

The World Health Organization, a UN agency founded in 1948, was first proposed at the 1945 UN Conference to coordinate global health efforts. This interactive timeline marks the WHO’s 75th anniversary with major public health milestones.

The modern Olympic truce originated in a real pause in ancient conflict

Back in Ancient Greece, neighboring city-states were constantly at war. So when the Olympics started in 776 BCE, they needed a way to keep the peace. This video from the International Olympic Committee discusses the origins of the Olympic Truce and its reinstatement at the 1994 Games in Lillehammer.

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

Some scholars consider the Bretton Woods system one of the best foreign policy decisions in US history

A survey of historians by the Council on Foreign Relations ranked the creation of the Bretton Woods system among the top 10 foreign policy decisions in US history, highlighting its role in establishing postwar stability, prosperity, and decades of economic growth.

The US Constitution is widely regarded as the longest-standing written national constitution still in force—see how it has influenced rights worldwide.

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

The US first hosted the World Cup in 1994, a tournament that lives in soccer infamy for its poor planning and the murder of Colombian player Andres Escobar, who'd accidentally scored on his own net.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

The United States has had a tumultuous relationship with Cuba since its 1959 revolution, highlighted by a nuclear crisis and a decades-long trade embargo.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

Double world record holder Hunter Ewen helped conquer his fear of balloons, called globophobia, by training to win Guinness World Record titles for balloon inflation.

During the French Revolution, a botanist's letter asking about "dear Rhus" (poison ivy) was intercepted, leading authorities to suspect he was conspiring with the Russians.

The most expensive ad of all time was for Chanel No. 5 perfume and cost roughly $33M to produce in 2004—about $57M in today's dollars.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

The idea for the Federal Reserve was conceived in secret in 1910—with bankers donning duck hunt gear for disguise while traveling to a remote country club on Georgia's Jekyll Island

The story of Dollree Mapp, whose legal challenge over her 1957 conviction for possessing "obscene material" led to a major strengthening of the Fourth Amendment

Learn how monoclonal antibodies, which mimic the body's antibodies, can fight diseases like Ebola.

70 years ago today, city officials in Santa Cruz, California, banned rock 'n' roll to protect its youth from corruption after witnessing a 'provocative' concert the night before.

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time

In preparation for this weekend's Eurovision finale, which is something like the World Cup of pop music, here's a young Céline Dion performing (for Switzerland?) at the 1988 competition.

Learn more about the history of fireworks, which dates back to an accidental invention during an alchemist's quest for information about immortality.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

The identity of the Tank Man in the iconic photo from the 1989 Tiananmen Square protests remains unknown and was possibly killed.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Domino's Pizza's 30-minute delivery guarantee was responsible for the chain's 1980s surge, but it was discontinued after the company was found liable for delivery driver accidents.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.