Chapter 3: Atmosphere and Climate

Class 9 Geography Notes

1. Atmosphere

Definition

The atmosphere is the blanket of gases surrounding the Earth. It is held around the Earth due to gravity.

Importance of Atmosphere

Provides oxygen for living beings.
Provides carbon dioxide for plants.
Protects Earth from harmful ultraviolet rays.
Maintains Earth’s temperature.
Helps in weather and rainfall formation.

2. Composition of Atmosphere

The atmosphere contains different gases:

Gas	Percentage	Importance
Nitrogen	78%	Helps plant growth
Oxygen	21%	Needed for breathing
Argon	0.93%	Inactive gas
Carbon dioxide	0.04%	Used by plants for photosynthesis
Other gases	Small amount	Includes ozone, helium, hydrogen etc.

Other components:

Water vapour
Dust particles

3. Structure of Atmosphere

The atmosphere has five main layers:

1. Troposphere

Lowest layer of atmosphere.
Extends up to about 12 km.
Contains air, clouds and water vapour.
All weather activities occur here.
Temperature decreases with height.

Remember: Weather = Troposphere

2. Stratosphere

Extends up to about 50 km.
Contains ozone layer.
Protects Earth from harmful UV rays.
Suitable for aircraft because there are fewer weather disturbances.

Remember: Ozone = Stratosphere

3. Mesosphere

Extends up to about 80 km.
Temperature decreases with height.
Meteors burn in this layer.

Remember: Meteors = Mesosphere

4. Thermosphere

Extends from about 80 km to 700 km.
Temperature increases rapidly.
Contains ionosphere.
Helps in radio communication.
Auroras occur here.

Remember: Radio + Aurora = Thermosphere

5. Exosphere

Outer-most layer.
Air is very thin.
Contains light gases like hydrogen and helium.

Layers of Atmosphere: Quick Revision Table

Layer	Important Feature
Troposphere	Weather occurs
Stratosphere	Ozone layer
Mesosphere	Meteors burn
Thermosphere	Auroras and radio waves
Exosphere	Outer boundary

4. Weather and Climate

Weather

Weather means the condition of atmosphere at a particular place and time.

Examples:

Rainy day
Sunny weather
Strong winds

Climate

Climate means the average weather conditions of a place over a long period (usually 30 years or more).

Difference Between Weather and Climate

Weather	Climate
Short-term condition	Long-term condition
Changes frequently	Changes slowly
Example: Today’s rainfall	Example: Desert climate

5. Elements of Weather and Climate

Temperature

Degree of hotness or coldness of air.
Controlled by sunlight received by Earth.
Temperature decreases from equator to poles.

Humidity

Amount of water vapour present in air.
High humidity makes the weather uncomfortable.

Precipitation

Water falling from atmosphere to Earth.
Forms:
- Rain
- Snow
- Hail
- Sleet

Atmospheric Pressure

Pressure exerted by the weight of air.
Highest at sea level.
Decreases with altitude.

Wind

Movement of air from high pressure to low pressure areas.

6. Local Winds

Sea Breeze

Occurs during daytime.
Wind moves from sea to land.
Land heats faster than sea.

Land Breeze

Occurs during night.
Wind moves from land to sea.
Land cools faster than sea.

7. Seasons in India

India has a tropical monsoon climate.

The four main seasons are:

1. Winter Season

December to early April

Cold season.
Northern India experiences low temperatures.

2. Summer Season

April to June

Hottest season.
Land becomes very hot.

3. Monsoon Season

June to September

Main rainy season.
South-west monsoon brings rainfall.

4. Post-Monsoon Season

October to December

Monsoon winds withdraw.
Tamil Nadu receives rainfall.

8. Monsoon

Definition

Monsoon is the seasonal reversal of wind direction.

Causes of Monsoon

Unequal heating of land and sea.
Difference in air pressure.
Movement of moisture-filled winds.

Types of Monsoon

South-West Monsoon

Occurs from June to September.
Brings most rainfall to India.
Winds move from sea to land.

North-East Monsoon

Occurs from October to February.
Winds move from land to sea.
Gives rainfall to Tamil Nadu and nearby areas.

Importance of Monsoon

Helps agriculture.
Provides water supply.
Supports economy.
Influences daily life.

9. Climate Change

Definition

Climate change refers to long-term changes in Earth’s temperature and weather patterns.

Causes

Burning fossil fuels
Deforestation
Industrial pollution

Greenhouse Gases

Important greenhouse gases:

Carbon dioxide
Methane
Nitrous oxide
Water vapour

These gases trap heat and increase Earth’s temperature.

Effects of Climate Change

Rising temperatures
Melting glaciers
Rising sea levels
Floods and droughts
Loss of biodiversity

10. Carbon Footprint

Definition

Carbon footprint is the amount of greenhouse gases released due to human activities.

Ways to Reduce Carbon Footprint

Save electricity
Use public transport
Plant trees
Reduce plastic use
Reuse and recycle
Use renewable energy

11. Punjab Floods Case Study

Causes

Natural Causes:

Heavy monsoon rainfall
River overflow
Western disturbances

Human Causes:

Weak embankments
Construction near rivers
Silt accumulation
Poor preparedness

Effects

Damage to crops
Loss of property
Displacement of people
Damage to roads and bridges
Health problems

Chapter Quick Revision

Remember:

Atmosphere → Layers → Weather → Seasons → Monsoon → Climate Change

Most Important Facts:

Nitrogen is the most abundant gas.
Troposphere is the weather layer.
Stratosphere contains ozone.
Monsoon is seasonal wind reversal.
India depends heavily on monsoon rainfall.
Climate change is mainly caused by human activities.

Important Exam Questions

1. What is atmosphere?

The atmosphere is the layer of gases surrounding Earth.

2. Name the layers of atmosphere.

Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.

3. Differentiate between weather and climate.

Weather is short-term atmospheric condition, while climate is long-term average weather condition.

4. Why is monsoon important for India?

Because agriculture, water supply, and economy depend on monsoon rainfall.

5. What causes climate change?

Burning fossil fuels, deforestation, and pollution increase greenhouse gases, causing climate change.

Complete Question Bank | Class 9 Geography

A. Multiple Choice Questions (MCQs)

1. The atmosphere is a layer of:

A. Water surrounding Earth
B. Rocks surrounding Earth
C. Gases surrounding Earth
D. Soil covering Earth

Answer: C. Gases surrounding Earth

2. The most abundant gas in the atmosphere is:

A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Argon

Answer: B. Nitrogen

3. Oxygen forms approximately what percentage of the atmosphere?

A. 78%
B. 50%
C. 21%
D. 10%

Answer: C. 21%

4. The gas used by plants for photosynthesis is:

A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Argon

Answer: C. Carbon dioxide

5. The lowest layer of the atmosphere is:

A. Stratosphere
B. Troposphere
C. Mesosphere
D. Exosphere

Answer: B. Troposphere

6. Weather changes mainly occur in:

A. Exosphere
B. Thermosphere
C. Troposphere
D. Mesosphere

Answer: C. Troposphere

7. The ozone layer is found in:

A. Troposphere
B. Stratosphere
C. Mesosphere
D. Exosphere

Answer: B. Stratosphere

8. Meteors burn up in which layer?

A. Troposphere
B. Stratosphere
C. Mesosphere
D. Thermosphere

Answer: C. Mesosphere

9. Radio communication is helped by:

A. Troposphere
B. Ionosphere
C. Exosphere
D. Mesosphere

Answer: B. Ionosphere

10. The outermost layer of the atmosphere is:

A. Thermosphere
B. Exosphere
C. Mesosphere
D. Stratosphere

Answer: B. Exosphere

11. Weather means:

A. Long-term atmospheric conditions
B. Daily atmospheric conditions
C. Ocean conditions
D. Landforms

Answer: B. Daily atmospheric conditions

12. Climate is studied over a period of about:

A. 5 years
B. 10 years
C. 30 years
D. 100 years

Answer: C. 30 years

13. The amount of water vapour present in air is called:

A. Pressure
B. Humidity
C. Temperature
D. Wind

Answer: B. Humidity

14. Rain, snow and hail are forms of:

A. Evaporation
B. Condensation
C. Precipitation
D. Radiation

Answer: C. Precipitation

15. Wind moves from:

A. Low pressure to high pressure
B. High pressure to low pressure
C. Sea to mountains only
D. Land to rivers

Answer: B. High pressure to low pressure

16. Sea breeze occurs during:

A. Night
B. Day
C. Winter only
D. Rainy season only

Answer: B. Day

17. Land breeze occurs during:

A. Day
B. Night
C. Afternoon only
D. Summer only

Answer: B. Night

18. India has mainly a:

A. Polar climate
B. Desert climate
C. Tropical monsoon climate
D. Mediterranean climate

Answer: C. Tropical monsoon climate

19. The rainy season in India mainly occurs from:

A. December to February
B. June to September
C. January to March
D. October to December

Answer: B. June to September

20. Monsoon means:

A. Heavy snowfall
B. Seasonal reversal of winds
C. Daily rainfall
D. Ocean current

Answer: B. Seasonal reversal of winds

21. The main rainy season of India is caused by:

A. North-east monsoon
B. South-west monsoon
C. Winter winds
D. Local winds

Answer: B. South-west monsoon

22. Tamil Nadu receives rainfall mainly from:

A. South-west monsoon
B. North-east monsoon
C. Western disturbances
D. Local winds

Answer: B. North-east monsoon

23. Climate change is mainly caused by:

A. Moonlight
B. Human activities
C. Ocean waves
D. Soil erosion only

Answer: B. Human activities

24. A major greenhouse gas is:

A. Nitrogen
B. Carbon dioxide
C. Oxygen
D. Argon

Answer: B. Carbon dioxide

25. Carbon footprint refers to:

A. Soil pollution
B. Amount of greenhouse gases released
C. Water pollution
D. Forest area

Answer: B. Amount of greenhouse gases released

B. Fill in the Blanks

The atmosphere is a layer of ______ surrounding Earth.
Answer: gases
______ is the most abundant gas in the atmosphere.
Answer: Nitrogen
Oxygen makes up about ______ of the atmosphere.
Answer: 21%
The ______ layer protects Earth from harmful UV rays.
Answer: ozone
Weather occurs in the ______ layer.
Answer: troposphere
Meteors burn in the ______ layer.
Answer: mesosphere
The outermost layer of atmosphere is called ______.
Answer: exosphere
The amount of water vapour in air is called ______.
Answer: humidity
Movement of air is called ______.
Answer: wind
Wind moves from ______ pressure to ______ pressure.
Answer: high, low
India receives most rainfall from the ______ monsoon.
Answer: south-west
Monsoon means seasonal ______ of winds.
Answer: reversal
Burning fossil fuels increases ______ gases.
Answer: greenhouse
Cutting down forests is called ______.
Answer: deforestation
Carbon footprint measures ______ gas emissions.
Answer: greenhouse

C. True or False

Nitrogen is the second most abundant gas in the atmosphere.
False
Weather occurs in the troposphere.
True
Ozone layer is found in the mesosphere.
False
Climate changes daily.
False
Humidity means water vapour present in air.
True
Wind moves from high pressure to low pressure.
True
Monsoon is related to seasonal wind changes.
True
South-west monsoon brings most rainfall to India.
True
Climate change has no connection with human activities.
False
Trees help reduce carbon dioxide in the atmosphere.
True

D. Match the Following

Column A	Column B
Troposphere	Weather
Stratosphere	Ozone layer
Mesosphere	Meteors
Thermosphere	Radio communication
Exosphere	Outer boundary

E. Very Short Answer Questions

1. What is atmosphere?

The atmosphere is the layer of gases surrounding Earth.

2. Name the two major gases of atmosphere.

Nitrogen and oxygen.

3. Which layer contains ozone?

Stratosphere.

4. Which layer is closest to Earth?

Troposphere.

5. What is monsoon?

Seasonal reversal of winds.

6. What is humidity?

The amount of water vapour present in air.

7. What is climate change?

Long-term change in climate patterns.

8. Name two greenhouse gases.

Carbon dioxide and methane.

F. Short Answer Questions

1. Why is atmosphere important?

2. Explain the importance of ozone layer.

3. Differentiate between weather and climate.

4. Explain the causes of monsoon.

5. Why is monsoon important for India?

6. Explain greenhouse effect.

7. How can we reduce carbon footprint?

8. Why do floods occur?

G. Long Answer Questions

1. Describe the five layers of atmosphere.

2. Explain the mechanism of Indian monsoon.

3. Discuss the causes and effects of climate change.

4. Explain the importance of atmosphere for life on Earth.

5. Describe the causes and effects of Punjab floods.

H. Assertion–Reason Questions

1. Assertion: Troposphere is important for humans.

Reason: All weather activities occur in this layer.

Answer: Both A and R are true, and R correctly explains A.

2. Assertion: Stratosphere is important for life.

Reason: It contains the ozone layer.

Answer: Both A and R are true, and R correctly explains A.

3. Assertion: Monsoon is important for Indian agriculture.

Reason: Most crops depend on rainfall.

Answer: Both A and R are true, and R correctly explains A.

I. Case-Based Question

Read the passage and answer:

“India receives most of its rainfall from monsoon winds. These winds change direction according to seasons due to differences in heating of land and sea.”

Questions:

What is monsoon?

Answer: Seasonal reversal of winds.

Which monsoon brings most rainfall?

Answer: South-west monsoon.

Why do monsoon winds occur?

Answer: Due to unequal heating of land and sea.