4. Ozone Depletion, Global Warming and Climate Change | The Three Terms Students Mix Up

This is the fourth topic post in Unit I — Introduction to Environmental Law. It moves from the scale of biodiversity within ecosystems to atmosphere-level environmental problems — the ones that dominate international environmental law, covered fully in Unit V.

The Problem This Topic Solves

Students routinely use "global warming," "climate change," and "ozone depletion" as if they were interchangeable — but they are three distinct atmospheric phenomena, with different causes, different mechanisms, and different legal responses. Getting them mixed up is one of the most common exam mistakes in this unit. This post separates the three clearly, and then shows how they connect.

Ozone Depletion

Ozone depletion is the thinning of the ozone layer in the Earth's stratosphere, caused by the breakdown of ozone (O₃) molecules. The ozone layer sits roughly 10 to 50 kilometres above the Earth's surface and absorbs nearly all of the Sun's harmful ultraviolet (UV-B and UV-C) radiation, shielding humans, wildlife, and ecosystems from it.

Causes of ozone depletion:

• Chlorofluorocarbons (CFCs) — once widely used in refrigerants, solvents, and aerosol propellants; once released, they rise into the stratosphere where UV radiation breaks them apart, releasing chlorine atoms that destroy ozone molecules
• Halons — used in fire extinguishers; release bromine, which breaks down ozone even more effectively than chlorine
• Other ozone-depleting substances (ODS) — carbon tetrachloride, methyl chloroform, and certain industrial solvents
• Nitrogen oxides (NOx) — from vehicle emissions, industrial activity, and biomass burning

Effects of ozone depletion: increased UV exposure raises the risk of skin cancer, cataracts, and weakened immune systems in humans; disrupts marine ecosystems (particularly phytoplankton, a base of the ocean food chain); reduces crop yields in UV-sensitive crops like wheat, rice, and soybeans. Some ozone-depleting substances are also potent greenhouse gases, which is the first link between this topic and global warming.

The international legal response — the Montreal Protocol, 1987 — is covered in full in Unit V; for this unit, know that it exists and successfully reduced global CFC use.

Global Warming

Global warming is the long-term increase in the Earth's average surface temperature, caused by the excessive accumulation of greenhouse gases (GHGs) in the atmosphere.

Causes of global warming:

• Greenhouse gases — carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and CFCs trap heat in the atmosphere
• Burning of fossil fuels — coal, oil, and natural gas used for energy release large quantities of CO₂
• Deforestation — reduces the Earth's capacity to absorb CO₂ through photosynthesis
• Industrial activities — release pollutants and GHGs through manufacturing
• Agricultural practices — livestock farming emits methane; fertilisers release nitrous oxide
• Urbanisation — construction and vehicle emissions add to the overall carbon footprint

Climate Change

Climate change refers to long-term shifts in temperature, precipitation, and weather patterns — global warming is its primary driver, but climate change is the broader, downstream consequence. Where global warming describes the rise in temperature itself, climate change describes everything that rise sets off.

Effects of global warming and climate change together:

• Extreme weather — heatwaves, droughts, floods, and storms occurring more frequently and intensely
• Melting ice and rising sea levels — glaciers and polar ice caps melt, threatening coastal regions
• Loss of biodiversity — species unable to adapt to shifting conditions face extinction
• Impact on agriculture — changing weather patterns threaten crop yields and food security
• Health issues — heatwaves, spread of vector-borne diseases, and pollution-linked respiratory issues
• Ocean acidification — increased CO₂ absorption by oceans lowers pH levels, harming corals and shellfish

The full international legal framework — Kyoto Protocol, UNFCCC, and the Paris Agreement — is covered in Unit V; this unit only needs the underlying phenomena.

• Ozone depletion — thinning of stratospheric ozone, caused mainly by CFCs and halons, resulting in higher UV exposure
• Global warming — rise in Earth's average surface temperature, caused by greenhouse gas accumulation
• Climate change — the broader, long-term shift in weather patterns caused by global warming
• Ozone layer location: stratosphere, ~10–50 km above Earth's surface; absorbs ~98–99% of harmful UV-B/UV-C radiation
• Some ozone-depleting substances are also greenhouse gases — the link between the two topics
• International responses (name only for this unit; full detail in Unit V): Montreal Protocol (ozone), Kyoto Protocol, UNFCCC, Paris Agreement (climate change)

Global Warming vs. Climate Change — At a Glance

How the three phenomena connect: Ozone Depletion (stratospheric ozone thins) → some ODS are also greenhouse gases → Global Warming (average surface temperature rises) → drives → Climate Change (broader, long-term shift in weather patterns).

A Practical Example

An old refrigerant (a CFC) leaks from an outdated air-conditioning unit. As it drifts up into the stratosphere, it breaks down ozone molecules — that is ozone depletion. The same CFC molecule also happens to trap heat in the atmosphere — contributing, alongside CO₂ from power plants and vehicles, to global warming. Over decades, that warming shifts monsoon patterns, melts glaciers feeding Indian rivers, and increases the frequency of heatwaves — that broader, cascading shift is climate change. One molecule, three distinct but connected phenomena.

Quick Revision Points

• Ozone depletion = stratospheric ozone thinning, caused by CFCs, halons, other ODS, and NOx
• Global warming = rise in average surface temperature, caused by greenhouse gas accumulation
• Climate change = the broader, long-term shift in weather patterns that global warming drives
• Ozone layer absorbs ~98–99% of harmful UV-B/UV-C radiation
• Some ODS are also greenhouse gases — the link between ozone depletion and global warming
• Detailed treaties (Montreal Protocol, Kyoto Protocol, UNFCCC, Paris Agreement) come in Unit V — know only that they exist for now