The Montreal Protocol and the Recovery of the Ozone Layer

Climate Change and the Ozone Crisis

Climate change refers to long‑term shifts in temperature and weather patterns. Although natural variations occur, human activity remains the primary driver. Burning fossil fuels, deforestation and biodiversity loss continue to threaten ecosystems and human health.

Since the 1930s, industries worldwide have released Chlorofluorocarbons into the atmosphere through refrigeration, air‑conditioning, aircraft halon, foam‑blowing agents and aerosol propellants. In 1985, scientists discovered a large hole in the ozone layer over Antarctica caused by chemical reactions between CFCs and ozone molecules. Approximately 40% of the ozone layer in that region had dissipated, creating what became known as the Ozone Hole.

The ozone layer, although thin, is essential. It absorbs UV‑B and UV‑C radiation, protecting living organisms from harmful ultraviolet exposure. Increased UV penetration contributes to global warming, rising sea levels and widespread ecological disruption.

A Call for Help: The Montreal Protocol

In 1987, UN Member States adopted the Montreal Protocol on Substances that Deplete the Ozone Layer. This multilateral environmental treaty contains 20 articles regulating the production and consumption of approximately 100 ozone‑depleting substances.

The Protocol divides controlled substances into 2 groups. Group 1 includes multiple types of CFCs. Group 2 includes other air pollutants, each listed with its ozone‑depleting potential.

Key obligations include:

• Article 2: control measures for consumption of ozone‑depleting substances.
• Article 3: calculation of control levels for production, import and export.
• Article 4: prohibition on importing ozone‑depleting substances from non‑party states.
• Article 6: assessment and review of control measures.
• Article 7: annual reporting requirements to the Secretariat of the Vienna Convention for the Protection of the Ozone Layer.
• Article 18: prohibition on reservations to ensure full compliance.

The Protocol was concluded on 16 September 1987 and entered into force on 1 January 1989 under Article 16. It is binding only upon ratification. Due to its urgency, all 198 UN Member States ratified it, making it the only UN treaty with universal ratification.

Recovery of the Ozone Layer

Implementation progressed effectively in both developed and developing states. Most adhered to the timetables set out in Article 5.

Although the Ozone Hole expanded to approximately 28.5 million square kilometres in 2000, states continued phasing out ozone‑depleting substances. Ultimately, 98% of these substances were eliminated from production and consumption. As a result, the Ozone Hole began shrinking at an estimated rate of 1 to 3% per decade. In 2019, it reached its smallest size since its discovery.

To commemorate the Protocol’s success, the UN General Assembly designated 16 September as the International Day for the Preservation of the Ozone Layer, also known as World Ozone Day.

The Kigali Amendment, 2016

Industries initially replaced CFCs with Hydrofluorocarbons. Although HFCs do not directly deplete ozone, they are powerful greenhouse gases. Greenhouse gases generally cool the stratosphere, which can support ozone recovery. However, in polar regions, lower temperatures increase the formation of polar stratospheric clouds, which accelerate ozone depletion.

To address this, the Montreal Protocol has been amended several times. The most recent amendment is the Kigali Amendment of 2016. Negotiations to phase down HFCs began in 2009. At the 28th Meeting of the Parties in Kigali, Rwanda, states agreed to reduce HFCs by approximately 85% by the 2040s. The amendment entered into force in 2019.

Final Note

The Montreal Protocol remains one of the most successful environmental treaties in history. It demonstrates the power of international cooperation and the effectiveness of legally binding environmental commitments. If compliance continues, the ozone layer is expected to fully recover by 2065.

Climate change, however, remains a broader challenge. Environmental law alone cannot solve it without state compliance and individual responsibility. Human health, ecosystems and global stability depend on continued action. Solutions exist, and progress begins with conscious choices, renewable alternatives and sustained global cooperation.