Greenhouse Effect, Global Warming and Ozone Depletion — Environmental Law Notes

Greenhouse Effect, Global Warming and Ozone Depletion

In 1985 three British scientists in Antarctica published data so startling their own instruments were re-checked for faults: a vast “hole” had opened in the ozone layer over the South Pole every spring. The world reacted with rare speed — within two years, nations signed the Montreal Protocol to phase out the chemicals responsible, and today the hole is slowly healing. It is the great success story of environmental law, and a useful warning: the atmosphere can be damaged faster than anyone expects, and repaired only when the law forces the change.

Two different problems, two different layers

This is the topic students most often get muddled, so fix the geography first. Both problems are about the atmosphere, but they happen in different layers, involve different gases, and are cured by different treaties. Keep them in separate boxes in your head:

The greenhouse effect and global warming are about heat trapped low down, in the layer of air nearest the ground (the troposphere).
Ozone depletion is about a protective shield being thinned high up, far above us (the stratosphere).

Get that one distinction right and the rest of the answer writes itself.

A. The greenhouse effect — a natural blanket

The greenhouse effect is a natural and necessary process. Certain gases in the air — mainly carbon dioxide, methane, nitrous oxide and water vapour — let the sun’s light in but trap some of the heat the earth radiates back out, just as the glass of a greenhouse keeps a garden warm. These are the greenhouse gases (GHGs). Without them the earth’s average temperature would be about −18°C, a frozen planet; with them it is a livable +15°C. So the greenhouse effect is not the villain — it is what makes life possible.

B. Global warming — the blanket grown too thick

The problem is too much of a good thing. Global warming is the rise in the earth’s average temperature caused by human activity thickening the greenhouse blanket. Burning fossil fuels (coal, oil, gas), cutting down forests that would have absorbed carbon dioxide, and industrial and farming emissions have pushed GHG levels far above their natural range. The blanket traps more heat, and the planet warms — this human-boosted version is called the enhanced greenhouse effect.

Its effects are the exam’s second paragraph:

Melting ice and rising seas — glaciers and polar ice melt, sea levels rise, and low-lying coasts and islands face flooding.
Extreme and erratic weather — more intense heatwaves, droughts, floods and cyclones, and a disrupted monsoon on which Indian agriculture depends.
Harm to life and food — shifting habitats drive species toward extinction, and changing rainfall and temperature threaten crops and water supply.

The controlling instruments — the “law” part of this topic — are international: the UN Framework Convention on Climate Change (UNFCCC), 1992 (agreed at the Rio Earth Summit), the Kyoto Protocol, 1997 (which set binding cuts in GHG emissions for developed countries on the principle of common-but-differentiated responsibilities), and the Paris Agreement, 2015 (in which nations pledged to keep warming well below 2°C). Remember: for greenhouse gases, the treaty is Kyoto (and later Paris).

C. Ozone depletion — the shield worn thin

Now go high up. The ozone layer is a band of ozone gas (O₃) in the stratosphere, roughly 15–35 km above the earth, and it does one priceless job: it absorbs most of the sun’s harmful ultraviolet (UV-B) radiation before it reaches us. It is the planet’s sunscreen.

Ozone depletion is the thinning of this shield by man-made chemicals called ozone-depleting substances (ODS) — chiefly chlorofluorocarbons (CFCs), once used in refrigerators, air-conditioners, aerosol sprays and foam, plus halons and similar compounds. When these rise into the stratosphere, sunlight breaks them apart and releases chlorine, and a single chlorine atom can destroy thousands of ozone molecules in a chain reaction. The worst thinning appears as the “ozone hole” over Antarctica each spring.

Its effects flow from the lost sunscreen: more UV reaching the surface means more skin cancer and cataracts in humans, weakened immune systems, and damage to crops and to the ocean plankton at the base of the marine food chain.

The controlling instruments here are the Vienna Convention, 1985 and — the key one — the Montreal Protocol, 1987, under which nations agreed to phase out CFCs and other ODS. It worked: the ozone layer is now recovering. For ozone, the treaty is Montreal.

⚠️ DON’T CONFUSE — greenhouse effect vs ozone depletion

These are two separate problems, and mixing them is the most common way to lose marks on this topic. Hold them apart on four points:

Layer: greenhouse/global warming happens in the troposphere (low, near the ground); ozone depletion in the stratosphere (high up).

Gases: greenhouse effect is caused by CO₂, methane, nitrous oxide; ozone depletion by CFCs and other ODS.

Harm: global warming traps heat and warms the planet; ozone depletion lets in UV radiation and causes cancer.

Treaty: the answer to GHGs is Kyoto/Paris; the answer to ODS is Montreal.

flowchart TD
    ROOT["Atmospheric damage"]:::root
    ROOT --> GW["GREENHOUSE / GLOBAL WARMING<br/>(troposphere — low)"]:::leaf
    ROOT --> OZ["OZONE DEPLETION<br/>(stratosphere — high)"]:::diamond
    GW --> GWc["Cause: CO2, methane, N2O<br/>from fossil fuels, deforestation"]:::leaf
    GW --> GWe["Effect: heat trapped, seas rise,<br/>extreme weather"]:::leaf
    GW --> GWt["Treaty: UNFCCC 1992,<br/>Kyoto 1997, Paris 2015"]:::leaf
    OZ --> OZc["Cause: CFCs / ODS<br/>release chlorine"]:::diamond
    OZ --> OZe["Effect: UV shield thinned,<br/>skin cancer, crop damage"]:::diamond
    OZ --> OZt["Treaty: Vienna 1985,<br/>Montreal 1987"]:::diamond
    classDef root fill:#FFF8DC,stroke:#000,stroke-width:1px,color:#000;
    classDef leaf fill:#E6F3FF,stroke:#1E3A8A,color:#000;
    classDef diamond fill:#FDECEA,stroke:#B22222,color:#000;
    linkStyle default stroke:#888,stroke-width:1px;

Case Laws

M.C. Mehta vs Union of India (1997) (the Taj Mahal / Taj Trapezium case) — to protect the Taj Mahal from air pollution the Supreme Court ordered polluting industries around Agra to switch to cleaner fuel or relocate; a leading Indian example of judicial control of harmful emissions.
M.C. Mehta vs Union of India (1998) (the Vehicular Pollution case) — the Court directed Delhi’s public transport to convert to CNG to cut vehicular emissions, showing the judiciary acting against air pollution that drives climate harm.
Vellore Citizens Welfare Forum vs Union of India (1996) — confirmed that international environmental principles (including precaution and sustainable development, the basis of the climate treaties) are part of Indian law.

📄 Full notes + Question Bank (₹199) — every topic in depth, model answers to all past KSLU questions, in one printable PDF. Get the bundle · 10 Solved Problems · All Environmental Law topics