Class 9 Social Science Chapter 3
Atmosphere and Climate
Understanding Society: India and Beyond – Grade 9 Part 1
Part 1 – Short Notes and Concepts
Chapter Summary
The atmosphere is the blanket of gases surrounding Earth. It provides essential gases for life, protects Earth from harmful solar radiation and helps control temperature, weather and climate. The atmosphere has five major layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Weather means the short-term condition of the atmosphere, while climate describes the average weather of a place over a long period. India’s climate is strongly influenced by the monsoon. Climate change is mainly linked with increasing greenhouse gases caused by human activities. Saving energy, reducing waste, using cleaner transport and protecting forests can help reduce our carbon footprint.
1. Composition of the Atmosphere
| Gas | Approximate Amount | Importance |
|---|---|---|
| Nitrogen | 78% | Essential for plant growth and living organisms. |
| Oxygen | 21% | Needed for respiration and combustion. |
| Argon | 0.93% | Present in small quantity. |
| Carbon dioxide | 0.04% | Used by plants in photosynthesis and helps regulate temperature. |
| Others | 0.03% | Includes gases such as helium, neon, krypton, xenon, ozone and hydrogen. |
The atmosphere also contains water vapour and tiny dust particles. Water vapour is important for cloud formation and precipitation.
2. Structure of the Atmosphere
| Layer | Approximate Height | Main Features |
|---|---|---|
| Troposphere | Surface to about 12 km | We live here. Most water vapour and clouds are present. Almost all weather occurs here. Temperature decreases with height. |
| Stratosphere | About 12–50 km | Contains ozone layer. Relatively free from clouds and weather disturbances. Suitable for aeroplanes. |
| Mesosphere | About 50–80 km | Temperature decreases with height. Most meteors burn here. |
| Thermosphere | About 80–700 km | Temperature rises rapidly. Absorbs high-energy solar radiation. Auroras occur here. Ionosphere is part of it. |
| Exosphere | Above thermosphere | Outermost layer with extremely thin air. Light gases can escape into space. |
3. Weather and Climate
| Weather | Climate |
|---|---|
| Short-term atmospheric condition. | Average weather condition over a long period. |
| Can change within hours or days. | Changes slowly over many years. |
| Example: Today’s rain or temperature. | Example: Tropical monsoon climate of India. |
4. Elements of Weather and Climate
- Temperature: Degree of hotness or coldness of air.
- Humidity: Amount of water vapour present in the air.
- Precipitation: Water falling from the atmosphere as rain, snow, sleet or hail.
- Atmospheric pressure: Pressure exerted by the weight of air.
- Wind: Movement of air from high-pressure areas towards low-pressure areas.
5. Insolation and Temperature
Insolation means incoming solar energy received by Earth. The Sun’s rays are more direct near the equator and more slanting towards the poles.
Therefore, temperature generally decreases from the equator towards the poles.
6. Winds
Wind is the movement of air from a high-pressure region towards a low-pressure region.
Sea Breeze
During the day, land heats faster than the sea. Air over the land rises, creating relatively low pressure. Cooler air moves from the sea towards the land. This is called sea breeze.
Land Breeze
At night, land cools faster than the sea. Air over the land becomes cooler and denser and moves towards the sea. This is called land breeze.
7. Four Main Seasons of India
| Season | Approximate Period |
|---|---|
| Winter | December to early April |
| Summer / Pre-monsoon | April to June, or up to July in north-western India |
| Monsoon / Rainy Season | June to September |
| Post-monsoon / Retreating Monsoon | October to December |
8. Traditional Indian Seasons
| Ṛtu | Indian Calendar | Approximate Gregorian Months |
|---|---|---|
| Vasanta | Chaitra–Vaiśhākha | March–April |
| Grīṣhma | Jyeṣhṭha–Āṣhāḍha | May–June |
| Varṣhā | Śhrāvaṇa–Bhādrapada | July–August |
| Śharad | Āśhvina–Kārtika | September–October |
| Hemanta | Mārgaśhīrṣha–Pauṣha | November–December |
| Śhiśhira | Māgha–Phālguna | January–February |
9. Monsoon
Monsoon means the seasonal reversal of wind direction.
South-West Monsoon
- Occurs mainly from June to September.
- Land heats faster than the surrounding ocean during summer.
- Low pressure develops over the Indian landmass.
- The ocean remains relatively cooler and has higher pressure.
- Moist winds move from the ocean towards land.
- These winds bring most of India’s annual rainfall.
North-East Monsoon
- Occurs mainly from October to February.
- Land cools faster than the surrounding ocean.
- High pressure develops over land.
- Winds generally move from land towards sea.
- After crossing the Bay of Bengal, they pick up moisture.
- They bring important rainfall to parts of south-eastern India, especially Tamil Nadu.
Agriculture, water supply, rivers, reservoirs, groundwater, transport, employment and many daily activities depend on monsoon rainfall. A weak monsoon can cause drought, while excessive rainfall can cause floods.
10. Climate Change
Climate change means long-term changes in temperature, rainfall, wind and other weather patterns.
Main human causes:
- Burning fossil fuels
- Deforestation
- Industrial pollution
- Excessive greenhouse-gas emissions
Major effects:
- Rising temperatures
- Melting glaciers
- Rising sea levels
- More frequent or intense floods and droughts
- Loss of biodiversity
- Effects on health, agriculture and livelihoods
11. How Can We Reduce Our Carbon Footprint?
- Walk or cycle for short distances.
- Use public transport or carpool.
- Save electricity.
- Switch off lights, fans and appliances when not required.
- Save water.
- Reuse and recycle materials.
- Avoid unnecessary single-use plastics.
- Plant and protect trees.
- Use renewable energy where possible.
- Adopt sustainable habits.
The Big Questions – Quick Answers
1. What is the composition of the atmosphere?
The atmosphere mainly consists of nitrogen and oxygen, along with
small amounts of argon, carbon dioxide and other gases, plus water vapour
and dust particles.
2. How do the different layers of the atmosphere affect the planet Earth?
They perform different functions such as supporting weather, protecting
Earth from harmful radiation, burning meteors, absorbing solar radiation
and supporting communication and auroras.
3. What is the mechanism of monsoon?
Seasonal heating and cooling of land and sea creates pressure differences.
Winds then reverse direction seasonally and bring rainfall to different
parts of India.
4. How can we reduce our carbon footprint?
By saving energy and water, using cleaner transport, reducing waste,
recycling, avoiding unnecessary plastic and protecting forests.
Part 2 – Book Solutions
The atmosphere is the blanket of gases surrounding the Earth. It is held around the Earth by gravity and is essential for life.
- Nitrogen – 78%
- Oxygen – 21%
- Argon – 0.93%
- Carbon dioxide – 0.04%
- Other gases – 0.03%
The atmosphere also contains varying amounts of water vapour and tiny dust particles.
Draw and label the five major layers in this order:
| Layer | Main Feature to Label |
|---|---|
| Exosphere | Outermost layer; very thin air |
| Thermosphere | Auroras; ionosphere |
| Mesosphere | Meteors burn here |
| Stratosphere | Ozone layer; aeroplanes |
| Troposphere | Weather, clouds and most water vapour |
At the bottom write Earth’s surface. Show altitude increasing upwards.
- Winter
- Summer or Pre-monsoon
- Monsoon or Rainy Season
- Post-monsoon or Retreating Monsoon
a. The troposphere and stratosphere
b. The south-west monsoon and north-east monsoon
a. The troposphere and stratosphere
| Troposphere | Stratosphere |
|---|---|
| Lowest atmospheric layer. | Lies above the troposphere. |
| Extends to about 12 km on average. | Extends up to about 50 km. |
| Most weather occurs here. | Very few weather disturbances occur here. |
| Contains most atmospheric water vapour and clouds. | Contains the ozone layer. |
| Temperature generally decreases with altitude. | Temperature generally increases with altitude. |
b. The south-west monsoon and north-east monsoon
| South-West Monsoon | North-East Monsoon |
|---|---|
| Mainly occurs from June to September. | Mainly occurs from October to February. |
| Winds generally move from sea towards land. | Winds generally move from land towards sea. |
| Brings most of India’s annual rainfall. | Generally dry over much of India but brings rainfall to parts of south-eastern India after crossing the Bay of Bengal. |
| Caused mainly by summer heating of land and pressure differences. | Associated with winter cooling of land and pressure differences. |
This is a graph-based activity. For each station:
- Put the months from January to December on the horizontal axis.
- Use a line graph for temperature.
- Use bars for rainfall.
- Compare the temperature and rainfall patterns.
Arrange them from nearest to the equator to farthest from the equator:
- Thiruvananthapuram – 8°29’N
- Bengaluru – 12°58’N
- Chennai – 13°4’N
- Mumbai – 19°N
- Nagpur – 21°9’N
- Kolkata – 22°34’N
- Shillong – 24°34’N
- Jodhpur – 26°18’N
- Delhi – 29°N
- Leh – 34°N
a. Two stations with the most extreme climate.
b. Two stations influenced by retreating monsoons.
c. The two hottest stations in the months of
(i) February (ii) June
a. Two stations with the most extreme climate
Delhi and Leh show very large temperature differences through the year and can be considered examples of more extreme climates in this table.
b. Two stations influenced by retreating monsoons
Chennai and Thiruvananthapuram are strongly influenced by the north-east/retreating monsoon period.
c. Two hottest stations
(i) February: Thiruvananthapuram and Chennai are among the hottest.
(ii) June: Jodhpur and Delhi are among the hottest in the given table.
a. Why does Shillong experience more rainfall than Kolkata?
b. Why does Delhi receive more rainfall than Jodhpur?
a. Why does Shillong experience more rainfall than Kolkata?
Shillong is located at a higher elevation and lies in a favourable position to receive moist monsoon winds. The surrounding hills force moist air to rise, causing heavy rainfall.
b. Why does Delhi receive more rainfall than Jodhpur?
Delhi is farther east and receives more moisture from the monsoon winds. Jodhpur lies deeper in the dry region of western India and receives much less monsoon rainfall.
a. Thiruvananthapuram has an equable climate?
b. Chennai has more rainfall only after the fury of the monsoon is over in most parts of the country?
c. Leh has moderate precipitation almost throughout the year?
a. Thiruvananthapuram has an equable climate?
Thiruvananthapuram is close to the sea. The sea reduces extreme temperature differences, giving the place an equable climate.
b. Chennai has more rainfall only after the fury of the monsoon is over in most parts of the country?
Chennai receives important rainfall from the north-east monsoon, which becomes active during the retreating monsoon period. The winds pick up moisture while crossing the Bay of Bengal.
c. Leh has moderate precipitation almost throughout the year?
Leh is a high-altitude region and lies in a rain-shadow area. It receives little rainfall, but some precipitation occurs during different parts of the year.
Yes. Although rainfall and temperature differ from place to place, the seasonal reversal of winds affects most parts of India. The south-west monsoon brings the main rainy season to much of the country, while the north-east monsoon affects parts of southern and south-eastern India. Thus, the monsoon gives India a broad seasonal and climatic unity.
Yes. Houses and clothing are often adapted to local climate and relief. For example:
| Region/Climate | Examples of Adaptation |
|---|---|
| Cold mountainous regions | Warm woollen clothes and houses designed to retain heat. |
| Hot and dry regions | Loose, light-coloured clothes and thick-walled houses that reduce heat. |
| Heavy rainfall regions | Sloping roofs help rainwater flow away quickly. |
| Flood-prone areas | Raised houses can help protect living spaces from floodwater. |
| Coastal regions | Houses and clothing are adapted to humid and warm conditions. |
Therefore, climate and relief influence the way people build houses and choose their clothing.
Chapter Activities – Easy Answers
Step 1: My Daily Habits
Choose one option from each group:
- Transport: Walking/cycling = 1; public transport/carpool = 2; private car for short trips = 3; frequent flights = 4.
- Electricity: Always switch off = 1; sometimes forget = 2; frequently leave on = 3.
- Water: Save water = 1; sometimes waste = 2; rarely save = 3.
- Waste: Reuse/recycle/avoid single-use plastic = 1; sometimes use disposable plastic = 2; frequently waste plastic = 3.
Step 2: Score Yourself
Add your points from all four categories.
Try to reduce your score through simple daily actions.
Step 3: My Climate Action Pledge
1. I will save electricity by switching off unused lights and appliances.
2. I will reduce plastic use and choose reusable items.
To what extent did natural factors cause these floods compared to human activities?
Heavy monsoon rainfall and swollen rivers were important natural causes. Human factors such as weak embankments, construction near rivers, sediment accumulation and inadequate communication of warnings increased the damage.
Do you think better planning could have reduced the damage? How?
Yes. Better flood forecasting, stronger embankments, proper drainage, keeping floodplains free from unsafe construction, timely evacuation and better disaster preparedness could reduce damage.
What are the guidelines for the management of floods according to the National Disaster Management Authority (NDMA)?
Important measures include early warning, evacuation planning, safe shelters, protection of critical infrastructure, drainage and community preparedness.
What role can students/youth play in helping with disaster preparedness?
Students can spread awareness, participate in preparedness drills, learn first aid, help communicate warnings responsibly and support community safety activities under adult and official guidance.
Before We Move On – Quick Revision
Climate: Average weather conditions over a long period.
Chapter 3 Complete
Atmosphere and Climate – Short Notes, Concepts, Activities and Complete Book Solutions