Atmosphere and Climate - Social Science Class 9 In English

Chapter 3. Atmosphere and Climate

Chapter Review

1. Atmosphere

The atmosphere is the blanket of air surrounding the Earth. It is held around the Earth by gravity and consists of a mixture of gases in different proportions. It is essential for the survival of all living beings.

The atmosphere protects the Earth from harmful radiation from the Sun, including ultraviolet radiation. It also regulates the Earth's temperature by trapping some of the Sun's energy. It plays an important role in weather and climate by influencing temperature, humidity, air pressure, wind, and precipitation.

2. Composition of the Atmosphere

The atmosphere consists mainly of nitrogen and oxygen along with small quantities of other gases, water vapour, and dust particles.

• Nitrogen: About 78% of the atmosphere.
• Oxygen: About 21% of the atmosphere.
• Argon: About 0.93%.
• Carbon dioxide: About 0.04%.
• Other gases: About 0.03%, including gases such as helium, neon, krypton, xenon, ozone, and hydrogen.

Water vapour is also present in the atmosphere. Its amount generally ranges from 0.1% to 0.4%. It plays an important role in cloud formation and precipitation.

3. Structure of the Atmosphere

The atmosphere has a layered structure. These layers are identified mainly on the basis of changes in temperature and density with increasing altitude.

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Exosphere

4. Troposphere

The troposphere is the lowest and most important layer of the atmosphere. Its average height is about 12 kilometres.

• Temperature decreases with increasing altitude.
• It contains the air that we breathe.
• Most of the water vapour and clouds are found in this layer.
• Almost all weather phenomena, such as rainfall, fog, and hail, occur here.
• The boundary between the troposphere and stratosphere is called the tropopause.

5. Stratosphere

The stratosphere lies above the troposphere and extends up to about 50 kilometres.

• It is relatively free from clouds and major weather disturbances.
• It is suitable for flying aeroplanes.
• It contains the ozone layer.
• Ozone absorbs harmful ultraviolet radiation from the Sun.
• The boundary between the stratosphere and mesosphere is called the stratopause.

6. Mesosphere

The mesosphere is the third major layer of the atmosphere and extends up to about 80 kilometres.

• Temperature decreases with increasing altitude.
• Most meteorites entering the Earth's atmosphere burn up in this layer.
• The boundary between the mesosphere and thermosphere is called the mesopause.

7. Thermosphere

The thermosphere extends approximately from 80 to 700 kilometres above the Earth's surface.

• Temperature rises rapidly with increasing altitude.
• Gas molecules absorb X-rays and short-wave ultraviolet radiation from the Sun.
• The ionosphere is a part of the thermosphere.
• It helps in radio transmission by reflecting radio waves towards the Earth.
• Auroras occur in this layer.

Aurora is a colourful display of light seen in the sky near the polar regions. It occurs when charged particles from the Sun interact with gases in the Earth's atmosphere.

The aurora in the Northern Hemisphere is called Aurora Borealis, while that in the Southern Hemisphere is called Aurora Australis.

8. Exosphere

The exosphere is the uppermost layer of the atmosphere. It is characterised by extremely thin air.

• Light gases such as helium and hydrogen are present.
• Due to weak gravity, some light gases can escape into space.

9. Weather

Weather refers to the hour-to-hour and day-to-day condition of the atmosphere at a particular place.

Weather can change significantly from one day to another. Temperature, humidity, wind, atmospheric pressure, and precipitation are important elements of weather.

10. Climate

Climate refers to the average weather conditions and variations of a place over a long period of time. It generally considers a period of about 30 years or more.

Difference: Weather describes short-term atmospheric conditions, whereas climate describes the long-term pattern of weather conditions over a large area.

11. Elements of Weather and Climate

The major elements that influence weather and climate are:

• Temperature
• Precipitation
• Humidity
• Wind
• Atmospheric pressure

12. Temperature and Insolation

Temperature refers to the degree of hotness or coldness of the atmosphere.

An important factor affecting the distribution of temperature is insolation.

Insolation is the incoming solar energy from the Sun that is intercepted by the Earth.

Insolation generally decreases from the equator towards the poles. Therefore, temperature also generally decreases from the equator towards the poles.

13. Humidity

Humidity refers to the presence of water vapour in the air.

Water evaporates from land and water bodies and enters the atmosphere as water vapour. When the amount of water vapour in the air is high, humidity is high.

Warm air can hold more water vapour than cold air. High humidity can make us feel uncomfortable because sweat evaporates more slowly.

14. Precipitation

Precipitation occurs when water vapour in the atmosphere condenses and falls to the Earth's surface due to gravity.

Forms of precipitation include:

• Drizzle
• Rain
• Snow
• Sleet
• Hail

Rain is the most common form of precipitation. Prevailing winds, mountains, and seasons influence precipitation.

15. Atmospheric Pressure

Atmospheric pressure is the pressure exerted by the weight of air on the Earth's surface.

• Atmospheric pressure is highest at sea level.
• It decreases rapidly with increasing altitude.
• Warm air rises and creates a low-pressure area.
• Cold air is heavier and sinks, creating a high-pressure area.
• Low-pressure areas are generally associated with cloudy and wet weather.
• High-pressure areas are generally associated with clear and sunny weather.

Air moves from areas of high pressure to areas of low pressure. This movement of air produces wind.

16. Wind

Wind is the movement of air from a high-pressure area towards a low-pressure area.

Wind may be gentle or strong. The direction of a wind is generally named after the direction from which it blows. For example, a wind blowing from the west is called a westerly.

17. Land Breeze

Land breeze is a local wind that blows from land towards the sea during the night.

At night, land cools faster than the sea. This difference in temperature and pressure causes air to move from land towards the sea.

18. Sea Breeze

Sea breeze is a local wind that blows from the sea towards the land during the day, especially in the afternoon.

During the day, land becomes warmer than the sea. The warmer air over the land rises and creates a low-pressure area. Air then moves from the sea towards the land.

19. Seasons in India

India has a broadly tropical monsoon climate. The Indian Meteorological Department (IMD) recognises four main seasons:

1. Winter Season: December to early April.
2. Summer or Pre-monsoon Season: April to June, or up to July in north-western India.
3. Monsoon or Rainy Season: June to September.
4. Post-monsoon or Retreating Monsoon Season: October to December.

The Himalayan states, because of their more temperate conditions, experience two additional seasons—autumn and spring.

20. Traditional Indian Seasons

Traditionally, India recognises six seasons, each generally lasting about two months:

21. Monsoon

Monsoon refers to the seasonal reversal in the direction of winds during a year.

The word monsoon is derived from the Arabic word mausim, meaning season.

Monsoon winds are seasonal winds and can be broadly classified into:

• South-west monsoon
• North-east monsoon

22. South-west Monsoon

The south-west monsoon is also known as the summer monsoon. It generally occurs from June to September.

During summer, the landmass of India heats up faster than the surrounding oceans. This creates a low-pressure area over the Indian subcontinent, while the relatively cooler Indian Ocean has higher pressure.

Since air moves from high-pressure areas to low-pressure areas, moisture-laden winds blow from the ocean towards the land and bring rainfall.

The south-west monsoon provides most of the rainfall received by India during the year.

23. North-east Monsoon

The north-east monsoon is also known as the winter monsoon. It generally occurs from October to February.

During winter, the Indian landmass cools faster than the surrounding oceans. This creates high pressure over the land and relatively low pressure over the seas.

Cold and dry winds generally blow from land towards the sea. However, when the north-east monsoon winds pass over the Bay of Bengal, they pick up moisture and bring rainfall to parts of the eastern coast, especially Tamil Nadu, Andhra Pradesh, and parts of Karnataka.

24. Importance of Monsoon in India

Monsoon plays a vital role in the lives and economy of people in India.

• Most Indian agriculture depends on monsoon rainfall.
• Farmers depend on rainfall for sowing and growing crops.
• A good monsoon helps maintain water in rivers, reservoirs, and wells.
• Monsoon influences daily life, transport, festivals, and employment.
• Excessive rainfall may cause floods.
• Weak monsoon rainfall may result in droughts.

Therefore, monsoon strongly influences India's economy, lifestyle, agriculture, and livelihoods.

25. Climate Change

Climate change refers to long-term changes in weather patterns such as temperature, rainfall, and wind.

Major human activities contributing to climate change include:

• Burning of fossil fuels
• Deforestation
• Industrial pollution
• Increasing greenhouse gas emissions

Greenhouse gases such as carbon dioxide, methane, nitrous oxide, and water vapour trap heat in the atmosphere and contribute to rising global temperatures.

26. Effects of Climate Change

Climate change can result in several environmental and social impacts:

• More frequent floods
• Droughts
• Melting of glaciers
• Rising sea levels
• Loss of biodiversity
• Impacts on agriculture
• Impacts on human health
• Disruption of livelihoods

27. Carbon Footprint

A carbon footprint is the total amount of greenhouse gases released into the atmosphere as a result of human activities such as energy use, transportation, and the production of goods and services.

28. Ways to Reduce Carbon Footprint

• Save electricity and energy.
• Use renewable sources of energy.
• Walk or cycle for short distances.
• Use public transport or carpool whenever possible.
• Reduce unnecessary use of private vehicles.
• Use water carefully and avoid wastage.
• Reuse and recycle materials.
• Avoid single-use plastics.
• Protect forests and plant trees.
• Adopt sustainable and environment-friendly lifestyles.

29. Punjab Floods 2025 – Case Study

In 2025, Punjab experienced severe floods due to heavy monsoon rainfall and the swelling of rivers such as the Satluj, Beas, and Ravi.

Natural causes included:

• Very heavy monsoon rainfall.
• Additional moisture and rainfall associated with western disturbances.
• Heavy rainfall in Punjab as well as neighbouring hill regions.
• High water levels in major rivers before additional heavy rainfall.

Human-made factors included:

• Weak or old river embankments.
• Construction of houses and farms too close to rivers.
• Accumulation of silt and mud in rivers and dams.
• Reduced capacity of rivers and dams to hold or carry water.
• Late or unclear flood warnings in some areas.

Effects of the floods included:

• Loss of human lives.
• Displacement of people to relief camps.
• Damage to agricultural fields and crops.
• Damage to poultry and dairy farms.
• Loss of livestock.
• Damage to roads, bridges, border fences, and public buildings.
• Health problems and waterborne diseases due to stagnant water.
• Economic losses, social disruption, and environmental damage.

Key Terms to Remember

• Atmosphere: The blanket of gases surrounding the Earth.
• Gravity: The force of attraction exerted by the Earth on objects near its surface.
• Altitude: The height of a place above mean sea level.
• Insolation: Incoming solar energy intercepted by the Earth.
• Humidity: The presence of water vapour in the air.
• Precipitation: Water falling from the atmosphere to the Earth's surface in forms such as rain, snow, sleet, and hail.
• Atmospheric Pressure: The pressure exerted by the weight of air on the Earth's surface.
• Wind: The movement of air from a high-pressure area to a low-pressure area.
• Monsoon: Seasonal reversal in the direction of winds during a year.
• Climate: The average weather conditions of a place over a long period, generally 30 years or more.
• Carbon Footprint: The total amount of greenhouse gases released due to human activities.

Quick Revision Points

• The atmosphere is essential for life and protects the Earth from harmful solar radiation.
• Nitrogen and oxygen are the two most abundant gases in the atmosphere.
• The five major atmospheric layers are Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
• Almost all weather phenomena occur in the troposphere.
• The ozone layer is found in the stratosphere and protects the Earth from harmful ultraviolet radiation.
• Most meteorites burn up in the mesosphere.
• Auroras occur in the thermosphere.
• Weather refers to short-term atmospheric conditions.
• Climate refers to long-term average weather conditions.
• Insolation generally decreases from the equator towards the poles.
• Air moves from high-pressure areas to low-pressure areas.
• Sea breeze blows from sea to land during the day.
• Land breeze blows from land to sea during the night.
• India has a broadly tropical monsoon climate.
• The IMD recognises four main seasons in India: Winter, Summer/Pre-monsoon, Monsoon, and Post-monsoon.
• Monsoon is a seasonal reversal of wind direction.
• The south-west monsoon brings most of India's annual rainfall.
• The north-east monsoon provides important rainfall to parts of south-eastern India.
• Climate change refers to long-term changes in weather patterns.
• Human activities such as fossil-fuel burning and deforestation contribute to climate change.
• Reducing energy consumption, using renewable energy, protecting forests, and adopting sustainable lifestyles can help reduce carbon footprints.