BharatNotes What is Ozone Depletion?
Ozone depletion is the chemical thinning of the stratospheric ozone layer, which lies roughly 10–50 km above the Earth's surface and absorbs most of the Sun's harmful ultraviolet-B (UV-B) radiation. The chief cause is ozone-depleting substances (ODS) — human-made chemicals containing chlorine or bromine, such as chlorofluorocarbons (CFCs), halons and carbon tetrachloride. Once these reach the stratosphere, UV radiation breaks them apart, releasing chlorine and bromine atoms that destroy ozone in a catalytic cycle — a single chlorine atom can destroy thousands of ozone molecules before being removed.
The most visible symptom is the seasonal Antarctic "ozone hole," which forms each spring (Sep–Oct) when extremely cold polar stratospheric clouds make chlorine highly reactive. A region is classed as part of the "hole" when ozone falls below the historical threshold of 220 Dobson Units (DU).
Discovery and the Global Response
The ozone hole was reported in May 1985 by British Antarctic Survey scientists Joseph Farman, Brian Gardiner and Jonathan Shanklin in Nature, based on data from Halley Bay. The decline was far larger than any model had predicted, prompting rapid diplomatic action.
| Milestone | Year | What it does | India |
|---|---|---|---|
| Vienna Convention | 1985 | Framework for research and cooperation (no binding controls) | Ratified 18 Mar 1991 |
| Montreal Protocol | 1987 (adopted 16 Sep) | Binding, step-wise phase-out of ODS; universally ratified | Party from 19 Jun 1992 |
| Kigali Amendment | 2016 | Phase-down of hydrofluorocarbons (HFCs) | Ratified Sep 2021 |
The Montreal Protocol gives developing countries (Article 5 parties) extra time and a Multilateral Fund to comply, and is the only UN treaty to achieve universal ratification.
Current Status (as of 2025)
Recovery is firmly on track. Per the 2022 Scientific Assessment of Ozone Depletion (WMO/UNEP), the ozone layer is projected to return to 1980 levels around 2066 over the Antarctic, ~2045 over the Arctic, and ~2040 for the rest of the world, if current policies hold.
- The 2024 Antarctic ozone hole was the 7th smallest since recovery began in 1992, averaging about 20 million sq km (7 Sep–13 Oct 2024), with a low of 109 DU on 5 Oct (NASA/NOAA).
- The 2025 hole was the 5th smallest since 1992, averaging ~18.71 million sq km, reaching a low of 147 DU on 6 Oct, and closing on 1 December 2025 — the earliest closure since 2019 (NASA/NOAA; WMO).
Why It Matters
The Kigali Amendment carries a major climate co-benefit: HFCs (the CFC replacements) are not ODS but are powerful greenhouse gases, and phasing them down is estimated to avoid 0.3–0.5°C of warming by 2100 (2022 Assessment). This makes ozone protection a rare win for both atmospheric health and climate goals — and the leading example of science-driven multilateralism succeeding.
