UNIT 7: Global Environmental Issues
7 MarksDetailed handwritten-style notes in very simple and easy English
Index / Contents
- Brief Introduction to Global Environmental Issues
- Climate Change and Global Warming
- Greenhouse Effect and Greenhouse Gases
- Causes of Climate Change and Global Warming
- Consequences of Climate Change and Global Warming
- Control and Prevention
- Ozone Layer and Ozone Layer Depletion
- Causes of Ozone Depletion
- Consequences of Ozone Depletion
- Control of Ozone Depletion
- Acid Rain
- Causes and Formation of Acid Rain
- Impacts of Acid Rain
- Control of Acid Rain
- Smog: Concept and Types
- Impacts of Smog
- Control of Smog
- Important Comparison Tables
- Quick Revision Sheet
- Board Exam Questions with Answers
- Practice Questions
1. Brief Introduction to Global Environmental Issues
Some environmental problems spread through the atmosphere, oceans and living systems. Because air, water and climate are connected, one country’s activities can affect people and nature in other countries.
Major global environmental issues
- Climate change: Long-term changes in temperature, rainfall and weather patterns.
- Global warming: Long-term rise in the average temperature of Earth.
- Ozone layer depletion: Reduction of ozone in the stratosphere.
- Acid rain: Rain or other precipitation made acidic by air pollutants.
- Smog: A mixture of smoke, gases, fog or sunlight-created pollutants near the ground.
- Loss of biodiversity: Reduction in species, genes and ecosystems.
- Desertification: Land degradation in dry areas.
- Pollution: Addition of harmful substances to air, water or soil.
2. Climate Change and Global Warming
Difference between weather and climate
| Weather | Climate |
|---|---|
| Condition of the atmosphere at a particular time and place. | Average pattern of weather over a long period. |
| Can change within minutes, hours or days. | Changes over many years or decades. |
| Example: Today is rainy. | Example: A region has a hot and dry climate. |
Simple relationship
Earth naturally has a greenhouse effect. This natural effect keeps Earth warm enough for life. The problem occurs when human activities increase greenhouse gases and make the warming stronger.
3. Greenhouse Effect and Greenhouse Gases
Important greenhouse gases
| Gas | Main sources |
|---|---|
| Carbon dioxide (CO₂) | Coal, petrol, diesel, gas, deforestation and cement production. |
| Methane (CH₄) | Rice fields, livestock, landfills, wetlands and fossil fuel production. |
| Nitrous oxide (N₂O) | Agricultural soils, fertilisers and combustion. |
| Water vapour | Natural water cycle; its amount increases as air becomes warmer. |
| Ozone (O₃) | Present naturally in the atmosphere; ground-level ozone is an air pollutant. |
| Fluorinated gases | Some industrial and refrigeration applications. |
Natural and enhanced greenhouse effect
Natural greenhouse effect
It is a natural process. It keeps Earth warm and supports life. Without it, Earth would be much colder.
Enhanced greenhouse effect
Human activities increase greenhouse gases. More heat is trapped, causing global warming and climate change.
4. Causes of Climate Change and Global Warming
A. Human causes
1. Burning of fossil fuels
Coal, petrol, diesel and natural gas are burned in power plants, vehicles, industries and homes. This releases large amounts of carbon dioxide.
2. Deforestation
Trees absorb carbon dioxide through photosynthesis. Cutting forests reduces carbon absorption and releases stored carbon when trees are burned or decay.
3. Industries and energy production
Factories and power stations release greenhouse gases during fuel burning and industrial processes.
4. Agriculture
- Rice fields can release methane.
- Cattle and other livestock produce methane.
- Excess use of nitrogen fertilisers can release nitrous oxide.
5. Transport
Cars, buses, trucks, ships and aircraft release carbon dioxide and other pollutants when fossil fuels are used.
6. Waste generation
Organic waste in landfills decomposes without oxygen and can produce methane.
B. Natural causes
- Volcanic eruptions.
- Changes in solar activity.
- Natural changes in ocean circulation.
- Natural variations in Earth’s climate system.
5. Consequences of Climate Change and Global Warming
1. Rise in temperature
Average temperatures increase, and heat waves may become more frequent or intense in many regions.
2. Melting of glaciers and ice sheets
Higher temperatures can melt glaciers and land ice. This contributes to sea-level rise and affects water availability in some regions.
3. Sea-level rise
Sea level rises mainly because seawater expands when warmed and because land ice melts. Coastal areas and islands may face flooding and erosion.
4. Changes in rainfall
Some areas may receive heavier rainfall, while others may experience droughts or irregular rainfall.
5. Extreme weather events
- Heat waves.
- Heavy rainfall and floods.
- Droughts.
- Strong storms in some regions.
- Wildfires in suitable dry and hot conditions.
6. Effects on agriculture
Changes in temperature, rainfall, pests and water availability can reduce crop productivity in some areas and disturb food security.
7. Effects on biodiversity
Species may shift their habitats, change breeding seasons or face extinction if they cannot adapt or move.
8. Human health effects
- Heat stress and dehydration.
- Spread of some vector-borne diseases.
- Respiratory problems due to heat and air pollution.
- Food and water insecurity.
9. Ocean changes
Oceans absorb heat and carbon dioxide. This can cause ocean warming and ocean acidification, affecting corals and marine organisms.
6. Control and Prevention of Climate Change
1. Reduce greenhouse gas emissions
- Use renewable energy such as solar and wind energy.
- Reduce unnecessary use of coal, petrol and diesel.
- Improve energy efficiency in buildings and industries.
- Use energy-efficient appliances and LED lights.
2. Promote afforestation and reforestation
Planting trees and restoring forests helps absorb carbon dioxide and protects soil, water and biodiversity.
3. Sustainable transport
- Use public transport, walking and cycling.
- Promote electric and low-emission vehicles.
- Share vehicles when possible.
4. Improve agriculture
Use efficient irrigation, balanced fertiliser use, improved rice cultivation and better livestock management.
5. Waste management
Follow the 5Rs: Refuse, Reduce, Reuse, Repair and Recycle. Compost organic waste and capture methane from landfills where possible.
6. Adaptation
- Early warning systems for floods and heat waves.
- Drought-resistant crops.
- Water conservation.
- Coastal protection and climate-resilient buildings.
- Disaster preparedness.
Mitigation and adaptation
| Mitigation | Adaptation |
|---|---|
| Reduces the causes of climate change. | Reduces damage caused by climate change. |
| Example: Renewable energy and tree planting. | Example: Flood protection and drought-resistant crops. |
7. Ozone Layer and Ozone Layer Depletion
Importance of the ozone layer
- Protects humans from harmful ultraviolet radiation.
- Reduces the risk of skin cancer and eye damage.
- Protects plants, crops and forests.
- Protects phytoplankton and aquatic ecosystems.
- Supports the balance of life on Earth.
Ozone hole
An ozone hole means a severe seasonal thinning of the ozone layer, especially observed over Antarctica. It does not mean that all ozone has completely disappeared.
8. Causes of Ozone Layer Depletion
1. Chlorofluorocarbons (CFCs)
CFCs were used in refrigerators, air conditioners, aerosol sprays and foam production. In the stratosphere, ultraviolet radiation breaks CFC molecules and releases chlorine atoms.
2. Halons
Halons were used in some fire-extinguishing systems. They can release bromine, which destroys ozone very effectively.
3. Other ozone-depleting substances
- Carbon tetrachloride.
- Methyl chloroform.
- Methyl bromide.
- Some hydrochlorofluorocarbons (HCFCs).
Simple chemical chain
One chlorine atom can take part in repeated reactions that destroy many ozone molecules. Polar stratospheric clouds also support special chemical reactions during the Antarctic winter and spring.
9. Consequences of Ozone Layer Depletion
1. Human health
- Increased risk of skin cancer.
- Eye problems such as cataracts.
- Weakening of the immune system.
- Skin damage and sunburn.
2. Plants and crops
Excess UV-B radiation can damage plant tissues, reduce photosynthesis and affect crop productivity.
3. Aquatic ecosystems
UV radiation can harm phytoplankton, which are important producers in aquatic food chains.
4. Materials
Strong UV radiation can damage plastics, rubber, paints and other materials.
10. Control of Ozone Layer Depletion
1. Reduce ozone-depleting substances
Stop or reduce the production and use of CFCs, halons and other ozone-depleting chemicals.
2. Use safer alternatives
Use technologies and refrigerants that have low or zero ozone-depleting potential and manage their emissions safely.
3. Follow international agreements
4. Safe handling of cooling equipment
- Prevent leakage from refrigerators and air conditioners.
- Recover and recycle refrigerants during repair or disposal.
- Train technicians in safe handling.
5. Public awareness
People should understand the harmful effects of ozone-depleting chemicals and support ozone-friendly products.
11. Acid Rain
Normal rain is slightly acidic because carbon dioxide dissolves in water and forms weak carbonic acid. Acid rain becomes more acidic mainly due to sulphuric acid and nitric acid formed from air pollutants.
Types of acid deposition
Wet deposition
Acidic substances reach the Earth through rain, snow, fog or mist.
Dry deposition
Acidic gases and particles settle directly on plants, soil, buildings and water surfaces without rain.
12. Causes and Formation of Acid Rain
Main pollutants
- Sulphur dioxide (SO₂): Released by burning coal and oil containing sulphur, metal smelting and some industries.
- Nitrogen oxides (NOₓ): Produced mainly during high-temperature combustion in vehicles, industries and power plants.
Formation of acid rain
Simple reactions:
SO₂ + oxygen → sulphur oxides → sulphuric acid
NOₓ + oxygen and water → nitric acid
Wind can carry these pollutants over long distances. Therefore, acid rain may affect regions far away from the original source of pollution.
13. Impacts of Acid Rain
1. Effects on aquatic ecosystems
Acid rain lowers the pH of lakes, ponds and streams. Fish, amphibians and aquatic microorganisms may be harmed, especially when water becomes highly acidic.
2. Effects on soil
- Removes useful nutrients such as calcium and magnesium.
- Can release toxic aluminium into soil water.
- Reduces soil fertility in sensitive areas.
3. Effects on forests and plants
Acid deposition can damage leaves, roots and soil nutrients. Trees may become weak and more sensitive to pests, cold and drought.
4. Effects on buildings and monuments
Acids react with limestone, marble and some metals. They can damage historical monuments, statues, buildings and bridges.
5. Human health
Acid rain itself is not usually the direct cause of most human health effects. However, the pollutants that cause it, especially fine particles and ozone-forming gases, can harm the respiratory and cardiovascular systems.
14. Control of Acid Rain
1. Reduce sulphur dioxide emissions
- Use low-sulphur fuels.
- Install flue-gas desulphurisation systems in industries.
- Use cleaner energy sources.
2. Reduce nitrogen oxides
- Use catalytic converters in vehicles.
- Improve combustion technology.
- Promote public transport and electric vehicles.
3. Renewable energy
Solar, wind and other low-emission energy sources reduce dependence on fossil fuels.
4. Energy conservation
Saving electricity reduces fuel burning and pollutant release.
5. Liming of affected lakes and soils
In some areas, crushed limestone or lime may be added to neutralise acidity. This is a corrective measure and does not replace pollution control.
6. Laws and monitoring
Emission standards, air-quality monitoring and international cooperation help reduce acid deposition.
15. Smog: Concept and Types
The word smog comes from the words smoke and fog.
Type 1: Classical or sulphurous smog
- Also called industrial smog.
- Commonly associated with coal burning and high sulphur pollution.
- Contains smoke, sulphur dioxide, particles and fog.
- Often forms in cool and humid conditions.
- Can cause serious breathing problems and poor visibility.
Type 2: Photochemical smog
- Forms when nitrogen oxides and volatile organic compounds react in sunlight.
- Common in sunny and warm conditions.
- Produces secondary pollutants such as ground-level ozone and PAN.
- Often appears as a brownish haze.
Formation of photochemical smog
Important terms
| Term | Meaning |
|---|---|
| NOₓ | Nitrogen oxides released mainly from combustion. |
| VOCs | Volatile organic compounds that evaporate easily and participate in chemical reactions. |
| Ground-level ozone | Secondary pollutant formed near the ground; harmful when inhaled. |
| PAN | Peroxyacetyl nitrate, an irritating component of photochemical smog. |
16. Impacts of Smog
1. Human health
- Eye, nose and throat irritation.
- Coughing and breathing difficulty.
- Asthma attacks and worsening of lung diseases.
- Chest discomfort and reduced lung function.
- Long-term exposure to air pollution can increase serious health risks.
2. Plants and crops
Ground-level ozone damages leaves, reduces photosynthesis and can lower crop yield.
3. Visibility and transport
Smog reduces visibility and increases the risk of road, aviation and other transport accidents.
4. Materials
Some smog pollutants damage rubber, paints, fabrics and other materials.
5. Environment
Smog disturbs ecosystems, affects sensitive plants and contributes to poor air quality in cities.
17. Control of Smog
1. Control vehicle emissions
- Use public transport, cycling and walking.
- Maintain vehicles properly.
- Use catalytic converters and cleaner fuels.
- Promote electric and low-emission vehicles.
2. Control industrial emissions
Use filters, scrubbers, cleaner technologies and proper emission monitoring in industries.
3. Reduce VOC emissions
- Use low-VOC paints and products.
- Prevent leakage of fuels and solvents.
- Store chemicals safely.
4. Avoid open burning
Do not burn leaves, plastic, crop waste or household garbage in open areas.
5. Increase green cover
Planting and protecting trees can help improve local environmental quality, although vegetation alone cannot replace emission reduction.
6. Public awareness and air-quality alerts
People should reduce outdoor exposure during severe smog episodes and follow official air-quality guidance.
18. Important Comparison Tables
Global warming and climate change
| Global warming | Climate change |
|---|---|
| Increase in average global temperature. | Long-term changes in temperature, rainfall, winds and climate patterns. |
| One major part of climate change. | Wider term that includes warming and other changes. |
Ozone depletion and global warming
| Ozone depletion | Global warming |
|---|---|
| Reduction of stratospheric ozone. | Increase in average Earth temperature. |
| Mainly caused by CFCs, halons and related substances. | Mainly caused by increased greenhouse gases. |
| Increases harmful UV radiation. | Changes climate and weather patterns. |
Classical and photochemical smog
| Classical smog | Photochemical smog |
|---|---|
| Associated with smoke, SO₂, particles and fog. | Formed from NOₓ and VOCs in sunlight. |
| Common in cool and humid conditions. | Common in warm, sunny conditions. |
| Often linked with coal burning. | Often linked with vehicle emissions. |
| Contains sulphurous pollutants. | Contains ozone, PAN and other oxidants. |
Acid rain and smog
| Acid rain | Smog |
|---|---|
| Mainly caused by SO₂ and NOₓ forming acids. | Mixture of gases, particles, smoke and chemical pollutants. |
| Deposits through wet or dry deposition. | Usually remains as polluted air near the ground. |
| Damages soil, water, forests and buildings. | Causes breathing problems, poor visibility and plant damage. |
19. Quick Revision Sheet
- Global environmental issues: Problems affecting many regions or the whole Earth.
- Global warming: Long-term rise in Earth’s average temperature.
- Climate change: Long-term change in climate patterns.
- Main greenhouse gases: CO₂, CH₄, N₂O, water vapour, ozone and fluorinated gases.
- Main climate causes: Fossil fuels, deforestation, industry, transport, agriculture and waste.
- Mitigation: Reducing the causes of climate change.
- Adaptation: Reducing damage from climate change.
- Ozone layer: Stratospheric ozone that absorbs harmful UV-B radiation.
- Ozone depletion: Reduction of stratospheric ozone by ozone-depleting substances.
- Main ozone-depleting substances: CFCs, halons and related chemicals.
- Montreal Protocol: International agreement to protect the ozone layer.
- Acid rain: Acidic precipitation caused mainly by SO₂ and NOₓ.
- Wet deposition: Acidic rain, snow, fog or mist.
- Dry deposition: Direct settling of acidic gases and particles.
- Smog: Polluted air containing smoke, gases, particles and other pollutants.
- Classical smog: Smoke + sulphur pollution + fog, usually in cool humid conditions.
- Photochemical smog: NOₓ + VOCs + sunlight → ozone, PAN and other pollutants.
20. Board Exam Questions with Answers
Very Short Answer Questions
Q1. Define global warming.
Answer: Global warming is the long-term rise in the average temperature of Earth mainly due to increased greenhouse gases.
Q2. What is climate change?
Answer: Climate change is a long-term change in temperature, rainfall, wind and other climate conditions.
Q3. Name any two greenhouse gases.
Answer: Carbon dioxide and methane.
Q4. What is the ozone layer?
Answer: The ozone layer is a region in the stratosphere containing ozone that absorbs harmful ultraviolet radiation.
Q5. Name two ozone-depleting substances.
Answer: CFCs and halons.
Q6. What is acid rain?
Answer: Acid rain is precipitation made more acidic by pollutants such as sulphur dioxide and nitrogen oxides.
Q7. What is smog?
Answer: Smog is polluted air containing a mixture of smoke, gases, particles and other pollutants.
Q8. Name the two major types of smog.
Answer: Classical smog and photochemical smog.
Short Answer Questions
Q1. Write four causes of global warming.
Answer: Burning fossil fuels, deforestation, industrial activities and transport are major causes. Agriculture and waste decomposition also release greenhouse gases.
Q2. Write four effects of climate change.
Answer: Climate change causes rising temperatures, melting glaciers, sea-level rise, irregular rainfall, extreme weather, biodiversity loss and health problems.
Q3. Explain the importance of the ozone layer.
Answer: The ozone layer absorbs harmful UV-B radiation. It protects humans from skin cancer and eye damage and protects plants, crops, phytoplankton and ecosystems.
Q4. Write the causes of acid rain.
Answer: Burning coal and oil, industrial processes and vehicle emissions release SO₂ and NOₓ. These gases react with oxygen and water in the atmosphere and form acids.
Q5. Differentiate between classical and photochemical smog.
Answer: Classical smog is associated with smoke, sulphur dioxide, particles and fog in cool humid conditions. Photochemical smog forms when NOₓ and VOCs react in sunlight and produce ozone and PAN.
Long Answer Questions
Q1. Explain global warming, its causes, effects and control measures.
Answer: Global warming is the long-term increase in Earth’s average temperature due mainly to increased greenhouse gases. Its causes include burning fossil fuels, deforestation, industries, transport, agriculture and waste. Its effects include melting glaciers, sea-level rise, changing rainfall, extreme weather, crop problems, biodiversity loss and health risks. It can be controlled by renewable energy, energy conservation, afforestation, sustainable transport, improved agriculture, waste management and international cooperation.
Q2. Explain ozone layer depletion and its control.
Answer: Ozone layer depletion is the reduction of stratospheric ozone. CFCs, halons and related substances release chlorine and bromine in the stratosphere. These chemicals destroy ozone molecules. Depletion increases harmful UV radiation and can cause skin cancer, eye damage, plant damage and harm to aquatic organisms. Control measures include reducing ozone-depleting substances, using safer alternatives, preventing refrigerant leakage, recycling refrigerants and following the Montreal Protocol.
Q3. Explain acid rain, its effects and control.
Answer: Acid rain is acidic precipitation formed mainly from sulphur dioxide and nitrogen oxides. These gases react with oxygen and water and form sulphuric and nitric acids. Acid rain damages lakes, fish, soil, forests, crops, buildings and monuments. It can be controlled by using low-sulphur fuel, renewable energy, emission-control devices, catalytic converters, public transport, energy conservation and strict pollution standards.
Q4. Define smog and explain its types, impacts and control.
Answer: Smog is polluted air containing smoke, gases, particles and other pollutants. Classical smog is associated with smoke, SO₂, particles and fog in cool humid conditions. Photochemical smog forms when NOₓ and VOCs react in sunlight and produce ozone and PAN. Smog causes eye irritation, breathing problems, reduced visibility, plant damage and transport problems. It can be controlled through cleaner vehicles, public transport, emission control, reduced VOC release, prevention of open burning and air-quality monitoring.
21. Practice Questions
- Define global environmental issues with examples.
- Differentiate between weather and climate.
- Define global warming and climate change.
- Explain the natural and enhanced greenhouse effect.
- Name six greenhouse gases or greenhouse gas groups.
- Describe the human causes of climate change.
- Explain five consequences of global warming.
- Differentiate between mitigation and adaptation.
- Define the ozone layer and explain its importance.
- What is ozone layer depletion?
- Explain the role of CFCs in ozone depletion.
- Write the effects of ozone depletion on humans and plants.
- Write a note on the Montreal Protocol.
- Define acid rain and explain wet and dry deposition.
- Explain the formation of acid rain using a flowchart.
- Write five impacts of acid rain.
- Describe methods for controlling acid rain.
- Define smog and explain its two types.
- Explain the formation of photochemical smog.
- Differentiate between classical and photochemical smog.
- Write the impacts and control measures of smog.
- Prepare a table comparing global warming, ozone depletion, acid rain and smog.
Exam Writing Tips ✍️
- Start every answer with a clear definition.
- For long questions, use the order: meaning → causes → effects → control.
- Remember the key gases: CO₂ and CH₄ for global warming; CFCs for ozone depletion; SO₂ and NOₓ for acid rain; NOₓ + VOCs + sunlight for photochemical smog.
- Draw flowcharts wherever possible.
- Underline keywords such as greenhouse effect, UV-B, CFCs, acid deposition, ozone and PAN.
- Use comparison tables for questions about smog and climate-related terms.
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