Home › Free notes › Class 9 Social Science › Atmosphere and Climate

Atmosphere and Climate – Class 9 Social Science notes, important questions and MCQs

NCERT Class 9 Social Science, chapter 3. Notes, key terms, important questions with answers and MCQs.

Chapter overview

The atmosphere is the blanket of air around the Earth that supports life, protects us from harmful rays and controls temperature. Weather is the day-to-day condition of the atmosphere, while climate is the average weather of a place over a long period. Factors such as latitude, altitude, distance from the sea and winds decide climate; India has a monsoon climate.

The atmosphere

Air is mainly nitrogen (about 78 per cent) and oxygen (about 21 per cent), with argon, carbon dioxide, water vapour and dust.
Layers from the surface upward: troposphere, stratosphere, mesosphere, thermosphere and exosphere.
All weather happens in the troposphere; the ozone layer in the stratosphere absorbs harmful ultraviolet rays.

Weather and climate

Elements of weather: temperature, air pressure, wind, humidity, clouds and precipitation.
Climate depends on latitude, altitude, distance from the sea, ocean currents, relief and winds.
Temperature falls by about 6.5 °C for every 1,000 metres of height.

India's monsoon climate

The monsoon is a seasonal reversal of winds: the south-west monsoon brings most of India's rain from June to September.
India has four seasons: cold weather, hot weather, advancing (rainy) monsoon and retreating monsoon.
Climate change caused by greenhouse gases is raising temperatures and making extreme weather more frequent.

Key terms

Atmosphere: the layer of gases surrounding the Earth
Troposphere: the lowest layer of the atmosphere, where all weather occurs
Climate: the average weather conditions of a place over a long period, usually 30 years or more
Monsoon: a seasonal reversal in the direction of winds that brings a rainy season
Greenhouse effect: the trapping of the Sun's heat by gases such as carbon dioxide in the atmosphere

Important questions with answers

Distinguish between weather and climate.2 marks

Weather is the condition of the atmosphere at a place for a short time, such as a day, and changes quickly. Climate is the average of weather conditions over a long period, usually 30 years or more, and changes very slowly.

Name the factors that affect the climate of a place.3 marks

The climate of a place is affected by latitude, which decides how much sunlight it gets; altitude, since temperature falls with height; distance from the sea, which moderates temperature; ocean currents, which may be warm or cold; relief, such as mountains that block winds; and the direction of prevailing winds.

Describe the structure of the atmosphere and explain the main features of India's monsoon climate.5 marks

The atmosphere is a blanket of gases around the Earth, mainly nitrogen (about 78 per cent) and oxygen (about 21 per cent), with small amounts of argon, carbon dioxide, water vapour and dust. It has five layers. The troposphere is the lowest, where all weather such as clouds, rain and storms occurs, and temperature falls with height. The stratosphere above it contains the ozone layer, which absorbs harmful ultraviolet rays. Above are the mesosphere, where meteors burn up, the thermosphere, which reflects radio waves, and the outermost exosphere. India has a monsoon climate, marked by a seasonal reversal of winds. In summer, moist south-west monsoon winds blow from the sea and bring most of India's rainfall from June to September. In winter, dry north-east winds blow from the land. India has four seasons: the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon. Rainfall is uneven, very heavy in the Western Ghats and the north-east and low in Rajasthan. The monsoon is vital for agriculture, water supply and the economy, and climate change is making it more uncertain.

Quick revision

Nitrogen 78 per cent, oxygen 21 per cent.
Troposphere = weather; stratosphere = ozone layer.
Climate controls: latitude, altitude, sea, winds, currents, relief.
Monsoon: seasonal reversal of winds; four seasons in India.

Exam tips

Weather = today; climate = long-term average. Use this line in answers.
Remember the layers in order with one fact each.

Practice MCQs

The most abundant gas in the atmosphere is
1. oxygen
2. carbon dioxide
3. nitrogen
4. argon
Show answer
Answer: (c) nitrogen. It forms about 78 per cent of air.
All weather phenomena occur in the
1. stratosphere
2. exosphere
3. mesosphere
4. troposphere
Show answer
Answer: (d) troposphere. It is the lowest layer.
The ozone layer protects us from
1. rain
2. wind
3. ultraviolet rays
4. dust storms
Show answer
Answer: (c) ultraviolet rays. It lies in the stratosphere.
The average weather of a place over a long period is called
1. weather
2. humidity
3. climate
4. pressure
Show answer
Answer: (c) climate. It is usually calculated over 30 years or more.
Temperature generally falls with height at about
1. 1 °C per 1,000 metres
2. 0 °C
3. 20 °C per 100 metres
4. 6.5 °C per 1,000 metres
Show answer
Answer: (d) 6.5 °C per 1,000 metres. That is why hill stations are cool.
Most of India's rainfall comes from the
1. south-west monsoon
2. retreating monsoon
3. western disturbances only
4. trade winds of the southern hemisphere directly
Show answer
Answer: (a) south-west monsoon. It arrives in June.
Why do coastal places have a moderate climate compared to inland places
1. they are at higher altitude
2. they are near the poles
3. they receive no wind
4. the sea heats and cools slowly, reducing temperature extremes
Show answer
Answer: (d) the sea heats and cools slowly, reducing temperature extremes. This is called the maritime influence.
An increase in greenhouse gases in the atmosphere leads to
1. global cooling
2. less evaporation
3. a thicker ozone layer
4. global warming
Show answer
Answer: (d) global warming. More heat is trapped near the surface.

All chapters of Class 9 Social Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.