Ozone Depletion and Atmospheric Change - TCE Environmental Science (Tasmania)
“Explain the role of the ozone layer, how human-made chemicals cause ozone depletion, and how international action has begun to reverse it.”
The ozone layer in the stratosphere absorbs most of the Sun's harmful ultraviolet radiation. Human-made chemicals called chlorofluorocarbons, once used in refrigeration and aerosols, drifted up and released chlorine that destroys ozone, creating a seasonal ozone hole over Antarctica. Thinner ozone lets more ultraviolet radiation reach the surface, raising rates of skin cancer and harming plankton and plants. The 1987 Montreal Protocol phased out these chemicals worldwide, and the ozone layer is now slowly recovering.
What this dot point is asking
This dot point asks you to explain what the ozone layer does, how human-made chemicals damaged it, and how the world responded. You should distinguish ozone depletion clearly from the greenhouse effect, describe the Antarctic ozone hole and its effects on living things, and explain why the Montreal Protocol is considered a successful example of international environmental management. Tasmania's southern location makes this issue locally relevant.
What the ozone layer does
Ozone is a molecule made of three oxygen atoms. High in the atmosphere, in the stratosphere, ozone forms a layer that absorbs most of the Sun's incoming ultraviolet radiation, especially the more damaging shorter wavelengths. By filtering out this radiation, the ozone layer protects living things at the surface from harm. Ultraviolet radiation damages DNA, so without this shield, rates of skin cancer, eye damage and harm to other organisms would be far higher.
It is important not to confuse this protective stratospheric ozone with ozone at ground level, which is a pollutant and a component of smog. The same molecule is beneficial high up and harmful near the surface.
How human chemicals deplete ozone
The damage was caused by a group of human-made chemicals, most importantly chlorofluorocarbons, or CFCs, once widely used as refrigerants, aerosol propellants and in foam manufacture. CFCs are very stable, so rather than breaking down near the ground they drift up into the stratosphere. There, intense ultraviolet light breaks them apart, releasing chlorine atoms. A single chlorine atom can catalyse the destruction of many thousands of ozone molecules before it is removed, which is why small quantities of CFCs caused such large damage.
Ozone depletion is the thinning of the stratospheric ozone layer caused by human-made chemicals such as CFCs releasing chlorine, which catalytically destroys ozone and lets more ultraviolet radiation reach the surface.
The Antarctic ozone hole
Depletion is most severe over Antarctica, where each spring an ozone hole forms, a region of greatly thinned ozone. The extreme cold of the polar winter creates special clouds on which the reactions that release chlorine occur, so when sunlight returns in spring, ozone is destroyed rapidly. The hole was first identified in the mid-1980s and grew alarmingly through the following decade.
Because Tasmania lies far south, closer to Antarctica than most populated places, it can experience elevated ultraviolet levels when the edge of the ozone-depleted air drifts north. This, combined with Australia's high baseline sunshine and fair-skinned population, helps explain why Australia has among the highest rates of skin cancer in the world and a strong public health focus on sun protection.
Impacts of increased ultraviolet radiation
Thinner ozone means more ultraviolet radiation reaches the surface, with consequences for health and ecosystems. In humans it raises rates of skin cancer, cataracts and immune suppression. In ecosystems it can damage phytoplankton, the tiny photosynthesising organisms at the base of marine food webs, which is a particular concern in the productive Southern Ocean. It can also harm the growth and reproduction of some plants, reducing agricultural and natural productivity.
Ozone depletion and the enhanced greenhouse effect are separate problems with separate causes. Ozone depletion lets in more ultraviolet radiation and is caused by CFCs; the enhanced greenhouse effect traps more heat and is caused mainly by carbon dioxide and methane. Keeping the two distinct is one of the clearest ways to show examiners you understand the mechanisms.
Data questions often track ozone-hole area or chlorine over time and ask you to explain recovery. Work through it in order.
Describe the trend with figures
State the start and end values for the ozone-hole area and the size of the change, for example a fall of about million km squared, and identify it as recovery.
Account for the time lag
Explain that the Montreal Protocol cut CFC production, but CFCs are long-lived, so atmospheric chlorine peaked years later and then fell slowly. Ozone recovery therefore lags the emission cut by years to decades.
Link cause to effect
Connect falling chlorine to slowing ozone destruction, so the hole stops growing and begins to shrink.
Evaluate the policy
Conclude that the trend shows the Montreal Protocol working, a model of effective international action backed by clear science and available substitutes, with full recovery expected mid-century.
The Montreal Protocol and recovery
The response to ozone depletion is widely regarded as the most successful international environmental agreement. The 1987 Montreal Protocol committed nations to phase out the production of CFCs and related chemicals, and it has been strengthened over time and ratified by virtually every country. Substitute chemicals were developed, and atmospheric chlorine levels have fallen. As a result, the ozone layer is slowly recovering and the Antarctic ozone hole is expected to close over coming decades. The success shows that coordinated global action, backed by clear science and available alternatives, can reverse a major environmental problem.
Bringing it together
To answer this dot point well, explain that stratospheric ozone absorbs harmful ultraviolet radiation, describe how CFCs release chlorine that catalytically destroys ozone, and explain the Antarctic ozone hole and its impacts on health and ecosystems. Stress the distinction from the greenhouse effect, note Tasmania's southern exposure, and conclude with the Montreal Protocol as a model of effective international environmental management.
The same molecule plays opposite roles depending on where it is. Stratospheric ozone shields life from ultraviolet radiation and we want to protect it; ground-level ozone is a harmful pollutant in smog. Make clear which ozone you mean, and never describe the protective layer as pollution.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice7 marksAtmospheric chlorine peaked around the mid-1990s and the Antarctic ozone hole reached a maximum area of about million km squared in 2000, easing to about million km squared by 2020. Using the data, describe the trend, explain the time lag between the chlorine peak and ozone recovery, and link it to the Montreal Protocol.Show worked answer →
A 7 mark data-and-explain question rewards a described trend, a lag explanation and the policy link.
- Describe the trend
- The ozone hole area fell from about million km squared in 2000 to about million km squared by 2020, a decline of roughly million km squared, indicating early recovery.
- Explain the time lag
- The 1987 Montreal Protocol cut CFC production, but CFCs are very long-lived, so atmospheric chlorine only peaked in the mid-1990s and then fell slowly. Because chlorine is removed gradually, ozone recovery lags years to decades behind the cut in emissions.
- Link to the Protocol
- The eventual decline shows the Protocol working: phasing out CFCs reduced chlorine, and ozone is slowly recovering, with full closure expected mid-century.
Markers reward the quantified decline, the long-lived-CFC lag, and the Montreal Protocol link.
Practice6 marksExplain why a single chlorine atom can destroy many ozone molecules, and why the ozone hole forms specifically over Antarctica in spring.Show worked answer →
A 6 mark explain question wants the catalytic mechanism plus the polar conditions.
Catalytic destruction. Ultraviolet light splits CFCs in the stratosphere, releasing chlorine atoms. Chlorine catalyses ozone breakdown: it reacts with ozone, is regenerated, and goes on to destroy thousands more ozone molecules before being removed, so a tiny amount of chlorine does large damage.
Antarctic spring. The extreme cold of the polar winter forms special stratospheric clouds on which chlorine is converted to its reactive form. When sunlight returns in spring, this primed chlorine destroys ozone rapidly, creating the seasonal hole.
Markers reward the regenerated-catalyst mechanism and the cold-cloud-plus-returning-sunlight explanation.