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.

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

Mario Molina and F. Sherwood Rowland discovered that chlorofluorocarbons released chlorine atoms that could break down molecules making up the protective ozone layer. Despite attempts to discredit scientists and economic concerns raised by politicians, the agreement to phase out ozone-depleting substances was signed in 1987.

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.

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.

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.

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.

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.

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.

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.

Hear firsthand how scientists and policymakers saved the ozone layer

In this episode, atmospheric chemist Susan Solomon and Protocol architect Stephen Andersen recount how scientific discovery, diplomacy, and public pressure drove the Montreal Protocol—and share lessons for tackling climate change.

How the Montreal Protocol made CFCs the most valuable Miami contraband after cocaine

Following the 1990s production ban, smugglers flooded Miami with illegal chlorofluorocarbons used in air conditioning. A 15-kilogram cylinder bought for $70 in Europe could sell for $242 in the US, fueling multimillion-dollar black-market trade. (Some users may experience a paywall.)

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.

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 EPA partners with other countries to strengthen environmental protection

Through bilateral programs on every continent, the EPA shares American environmental expertise with developing nations and economies in transition. These partnerships support air and water protection, chemical safety, and pollution control, while advancing US environmental priorities abroad.

Why the ozone hole altered Southern Hemisphere jet streams and rainfall patterns

Ozone depletion over Antarctica shifted jet streams southward, drying Australia while increasing rainfall in Uruguay, Brazil, Paraguay, and Argentina. Around the turn of the millennium, these trends began to slow as the Montreal Protocol phased out ozone-depleting substances.

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.

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 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.

Fluorinated molecules are the most impactful, longest-lasting greenhouse gases

Developed as replacements for ozone-depleting substances in refrigeration and air conditioning systems, these compounds are released through leaks in and ongoing use of these appliances, as well as from various industrial processes. They can remain in the atmosphere for thousands of years and have warming potentials that are a thousand to tens of thousands of times greater than those of carbon dioxide.

The IMF was created to prevent the currency crises that destabilized the 1930s global economy

Founded in 1945, the IMF monitors exchange rates, promotes financial stability, and provides emergency funding to countries that cannot pay for their imports. It currently has 191 member countries and acts as a lender of last resort for struggling economies.

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.

Ozone protects against the sun's UV radiation and enhances the greenhouse effect

In the stratosphere, trioxygen molecules can absorb harmful ultraviolet radiation from the sun, preventing it from reaching Earth's surface, where it can harm organisms and raise surface temperatures. In the lower atmosphere, ozone acts as a greenhouse gas, trapping thermal radiation.

When signing the Paris Agreement, almost 200 nations committed to pursuing efforts to limit global warming to 1.5 degrees Celsius above preindustrial levels, based on guidance from the Intergovernmental Panel on Climate Change.

The World Bank funds development in the world's poorest countries

Originally called the International Bank for Reconstruction and Development, the World Bank was established in 1944 to assist in rebuilding war-damaged countries and has since grown to finance long-term economic development worldwide.

Why the Antarctic climate enabled British scientists to discover the ozone hole

In the Antarctic stratosphere, polar conditions facilitate the formation of polar stratospheric clouds, which allow chlorine compounds from chlorofluorocarbons to accumulate. In 1985, British Antarctic Survey scientists detected massive springtime losses over Antarctica, as accumulated compounds destroyed significant amounts of ozone once sunlight returned.

The Clean Air Act became the cornerstone of modern air pollution control

Passed in 1970 and strengthened through multiple amendments, the Clean Air Act authorizes the EPA to set national air quality standards, regulate industrial and vehicle emissions, and reduce pollutants such as ozone, sulfur dioxide, and lead.

Environmental regulation had bipartisan support in the 1970s

During the 1970s, Democrats and Republicans alike backed landmark environmental laws. Congress passed the Clean Air, Clean Water, and Endangered Species Acts with overwhelming bipartisan majorities—reflecting broad public agreement on protecting the environment.

Why bacterial bioremediation may help counter the negative effects of past chemical solutions

Molecules such as DDT, a synthetic insecticide, and PFAS—"forever" chemicals used to make products resistant to heat, water, and grease—have historically been used across various industries but are now known to be harmful. Microbes that can convert some of these substances into nontoxic products, such as water and carbon dioxide, have already been identified, with ongoing research to find others.

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.

Critics argue that the World Bank, IMF, and WTO were designed to serve Western interests

Some analysts from developing nations argue that the Bretton Woods institutions were designed to reinforce Western economic dominance rather than to promote fair development for poorer countries. Supporters respond that these institutions have improved living standards worldwide.

The Bretton Woods conference in 1944 created the foundations of the modern global economy

In July 1944, 44 nations gathered in Bretton Woods, New Hampshire, to create a new postwar economic order. The conference led to the creation of the IMF and the International Bank for Reconstruction and Development—now known as the World Bank.

Microfinance, conceived as a solution to conservative critics of Western aid as a handout system in the 1980s, is a small-dollar, community-based financing structure that was originally created as a way to expand access to credit and end poverty.

Norway operates the largest SWF in the world—managing more than $2T in assets

The fund is considered the gold standard SWF because of its transparency around investments, politically independent governance, and strong ethical boundaries that serve as the backbone of the investment philosophy. For example, fund managers will not invest in coal, tobacco, or nuclear weapons, because these investments are considered harmful to humanity.

The 1997 Asian financial crisis tested the limits of the rules-based order's financial architecture

When a currency crisis hit Thailand, Indonesia, and South Korea, the IMF allocated $118B in emergency loans. However, the attached conditions were widely criticized for worsening the economic downturn and increasing distrust of Western-led institutions across the Global South.

Carbon markets incentivize companies to cut emissions but require high carbon prices

To reduce greenhouse gas emissions, a cap-and-trade system issues a limited number of emissions permits—carbon credits—that decrease each year, cutting into a company's profits if it does not reduce emissions and must buy permits from others. However, cheap permits and minimal fines for lacking permits have reduced the system's effectiveness.

The Non‑Proliferation Treaty was designed to prevent new states from developing nuclear bombs

The Treaty on the Non‑Proliferation of Nuclear Weapons (created in 1968, effective 1970) binds non-nuclear states to forgo nuclear weapons and commits nuclear powers to share peaceful technology and pursue disarmament—forming the core of the global non-proliferation regime.

The Marshall Plan aimed to rebuild Europe and limit Soviet influence

Launched in 1948, the Marshall Plan provided over $12B (roughly $150B today) in US aid to help rebuild Western Europe. While framed as economic recovery, it also served as a Cold War tool—tying countries to the US and excluding the Soviet bloc.

As of 2023, more than 130 nations have enacted bans or restrictions on plastic items, starting with Bangladesh's ban on plastic bags in 2002.

Transit is funded through a three-tier system, and the federal government is the smallest piece

In 2019, the federal government covered about one-sixth of the $79B spent on public transit. States and localities make up the rest. About 85% of all transit trips are taken by bus or heavy rail, and nearly 4 in 10 US transit trips occur in the New York City metro area.