7.4.2 Impacts of Ozone Depletion
Dermatological Impacts: Increased UV-B exposure is a primary driver for non-melanoma skin cancers (basal and squamous cell carcinomas) and increases the risk of malignant melanoma. This occurs because UV-B induces pyrimidine dimers in DNA, leading to mutations during cell replication.
Ocular Damage: The lens of the human eye is sensitive to UV radiation. Chronic exposure accelerates the denaturation of lens proteins, leading to cataracts, which is a leading cause of blindness globally.
Immune Suppression: UV-B radiation can suppress the body's immune response by affecting the activity and distribution of cells responsible for triggering immune reactions. This may reduce the effectiveness of vaccinations and increase susceptibility to infectious diseases.
Plant Physiology: In terrestrial plants, high UV-B levels can alter growth patterns, reduce leaf area, and change the timing of flowering. While some plants have evolved UV-shielding pigments (like flavonoids), many crops show reduced yields and biomass under high UV stress.
Marine Food Webs: Phytoplankton, the foundation of aquatic food webs, reside near the ocean surface to access sunlight for photosynthesis. Increased UV-B reduces their productivity and survival rates, which can cause a bottom-up collapse of the entire marine ecosystem.
Developmental Vulnerability: Early life stages of fish, amphibians, and crustaceans are particularly vulnerable to UV-B. Exposure during these stages can cause developmental abnormalities and high mortality rates in shallow-water habitats.
Carbon Cycle Disruption: By reducing the photosynthetic capacity of terrestrial plants and marine phytoplankton, ozone depletion can decrease the rate of carbon dioxide () sequestration. This creates a feedback loop that may exacerbate the greenhouse effect.
Material Degradation: Synthetic polymers (plastics), wood, and other biopolymers are susceptible to photodegradation. UV-B radiation breaks the polymer chains, leading to discoloration, loss of mechanical strength, and reduced lifespan of outdoor materials.
Atmospheric Chemistry: Increased UV-B alters the chemical reactivity of the lower atmosphere (troposphere). It can increase the production of tropospheric ozone (a pollutant and greenhouse gas) and affect the concentration of hydroxyl radicals (), which clean the atmosphere of other gases.
| Feature | Ozone Depletion | Global Warming (Climate Change) |
|---|---|---|
| Primary Cause | Chlorofluorocarbons (CFCs) and Halons | Greenhouse gases (, , ) |
| Main Mechanism | Chemical destruction of molecules | Trapping of infrared radiation (heat) |
| Primary Impact | Increased UV-B radiation | Increased global mean temperature |
| Location | Stratosphere (Upper atmosphere) | Troposphere (Lower atmosphere) |
Identify the Radiation Type: Always specify UV-B when discussing ozone depletion. Mentioning 'sunlight' or 'heat' in general is often too vague for full marks.
Mechanism of Damage: When asked how UV-B causes cancer, focus on DNA damage and mutation rather than 'burning' the skin. The long-term genetic impact is the key scientific concept.
Ecosystem Links: Remember the 'bottom-up' effect. If a question asks about fish populations, connect it back to the impact on phytoplankton and the food chain.
Material Science: If a question mentions 'polymers' or 'plastics' in the context of the environment, consider UV-B degradation as a primary factor for material failure.